# drafts

name: draft-ietf-hpke-hpke
rev: 02
title: Hybrid Public Key Encryption
time: 2025-11-04T15:14:47Z
group_uri: /api/v1/group/group/2448/
expires: 2026-05-08T15:14:47Z
states: ["/api/v1/doc/state/1/", "/api/v1/doc/state/150/", "/api/v1/doc/state/38/"]
categories: ["Agent identity/auth", "Data formats/interop"]
tags: []
fetched_at: 2026-02-27T22:56:09.014920+00:00
abstract:
This document describes a scheme for hybrid public key encryption
   (HPKE).  This scheme provides a variant of public key encryption of
   arbitrary-sized plaintexts for a recipient public key.  It also
   includes a variant that authenticates possession of a pre-shared key.
   HPKE works for any combination of an asymmetric KEM, key derivation
   function (KDF), and authenticated encryption with additional data
   (AEAD) encryption function.  We provide instantiations of the scheme
   using widely used and efficient primitives, such as Elliptic Curve
   Diffie-Hellman (ECDH) key agreement, HMAC-based key derivation
   function (HKDF), and SHA2.

full_text:
HPKE                                                           R. Barnes
Internet-Draft                                                     Cisco
Obsoletes: 9180 (if approved)                               K. Bhargavan
Intended status: Standards Track                                 B. Lipp
Expires: 8 May 2026                                                Inria
                                                                 C. Wood
                                                         4 November 2025


                      Hybrid Public Key Encryption
                        draft-ietf-hpke-hpke-02

Abstract

   This document describes a scheme for hybrid public key encryption
   (HPKE).  This scheme provides a variant of public key encryption of
   arbitrary-sized plaintexts for a recipient public key.  It also
   includes a variant that authenticates possession of a pre-shared key.
   HPKE works for any combination of an asymmetric KEM, key derivation
   function (KDF), and authenticated encryption with additional data
   (AEAD) encryption function.  We provide instantiations of the scheme
   using widely used and efficient primitives, such as Elliptic Curve
   Diffie-Hellman (ECDH) key agreement, HMAC-based key derivation
   function (HKDF), and SHA2.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Source for this draft and an issue tracker can be found at
   https://github.com/hpkewg/hpke.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 8 May 2026.



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Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   4
   3.  Notation  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Cryptographic Dependencies  . . . . . . . . . . . . . . . . .   5
     4.1.  DH-Based KEM (DHKEM)  . . . . . . . . . . . . . . . . . .   9
   5.  Hybrid Public Key Encryption  . . . . . . . . . . . . . . . .  11
     5.1.  Creating the Encryption Context . . . . . . . . . . . . .  12
       5.1.1.  Encryption to a Public Key  . . . . . . . . . . . . .  15
       5.1.2.  Authentication Using a Pre-Shared Key . . . . . . . .  16
     5.2.  Encryption and Decryption . . . . . . . . . . . . . . . .  16
     5.3.  Secret Export . . . . . . . . . . . . . . . . . . . . . .  18
   6.  Single-Shot APIs  . . . . . . . . . . . . . . . . . . . . . .  19
     6.1.  Encryption and Decryption . . . . . . . . . . . . . . . .  19
     6.2.  Secret Export . . . . . . . . . . . . . . . . . . . . . .  20
   7.  Algorithm Identifiers . . . . . . . . . . . . . . . . . . . .  20
     7.1.  Key Encapsulation Mechanisms (KEMs) . . . . . . . . . . .  20
       7.1.1.  SerializePublicKey and DeserializePublicKey . . . . .  21
       7.1.2.  SerializePrivateKey and DeserializePrivateKey . . . .  21
       7.1.3.  DeriveKeyPair . . . . . . . . . . . . . . . . . . . .  22
       7.1.4.  Validation of Inputs and Outputs  . . . . . . . . . .  24
       7.1.5.  Future KEMs . . . . . . . . . . . . . . . . . . . . .  24
     7.2.  Key Derivation Functions (KDFs) . . . . . . . . . . . . .  25
       7.2.1.  Input Length Restrictions . . . . . . . . . . . . . .  25
     7.3.  Authenticated Encryption with Associated Data (AEAD)
           Functions . . . . . . . . . . . . . . . . . . . . . . . .  27
   8.  API Considerations  . . . . . . . . . . . . . . . . . . . . .  27
     8.1.  Auxiliary Authenticated Application Information . . . . .  27
     8.2.  Errors  . . . . . . . . . . . . . . . . . . . . . . . . .  28
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  29
     9.1.  Security Properties . . . . . . . . . . . . . . . . . . .  29
       9.1.1.  Computational Analysis  . . . . . . . . . . . . . . .  30
       9.1.2.  Post-Quantum Security . . . . . . . . . . . . . . . .  31



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     9.2.  Security Requirements on a KEM Used within HPKE . . . . .  31
       9.2.1.  Encap/Decap Interface . . . . . . . . . . . . . . . .  32
       9.2.2.  KEM Key Reuse . . . . . . . . . . . . . . . . . . . .  32
     9.3.  Security Requirements on a KDF  . . . . . . . . . . . . .  32
     9.4.  Security Requirements on an AEAD  . . . . . . . . . . . .  32
     9.5.  Pre-Shared Key Recommendations  . . . . . . . . . . . . .  32
     9.6.  Domain Separation . . . . . . . . . . . . . . . . . . . .  33
     9.7.  Application Embedding and Non-Goals . . . . . . . . . . .  34
       9.7.1.  Message Order and Message Loss  . . . . . . . . . . .  34
       9.7.2.  Downgrade Prevention  . . . . . . . . . . . . . . . .  35
       9.7.3.  Replay Protection . . . . . . . . . . . . . . . . . .  35
       9.7.4.  Forward Secrecy . . . . . . . . . . . . . . . . . . .  36
       9.7.5.  Bad Ephemeral Randomness  . . . . . . . . . . . . . .  37
       9.7.6.  Hiding Plaintext Length . . . . . . . . . . . . . . .  37
     9.8.  Bidirectional Encryption  . . . . . . . . . . . . . . . .  37
     9.9.  Metadata Protection . . . . . . . . . . . . . . . . . . .  38
   10. Message Encoding  . . . . . . . . . . . . . . . . . . . . . .  38
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  39
     11.1.  KEM Identifiers  . . . . . . . . . . . . . . . . . . . .  39
     11.2.  KDF Identifiers  . . . . . . . . . . . . . . . . . . . .  40
     11.3.  AEAD Identifiers . . . . . . . . . . . . . . . . . . . .  40
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  41
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  41
     12.2.  Informative References . . . . . . . . . . . . . . . . .  41
   Appendix A.  Differences from RFC 9180  . . . . . . . . . . . . .  45
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .  45
   Appendix C.  Test Vectors . . . . . . . . . . . . . . . . . . . .  46
     C.1.  DHKEM(X25519, HKDF-SHA256), HKDF-SHA256, AES-128-GCM  . .  46
       C.1.1.  Base Setup Information  . . . . . . . . . . . . . . .  46
       C.1.2.  PSK Setup Information . . . . . . . . . . . . . . . .  49
     C.2.  DHKEM(X25519, HKDF-SHA256), HKDF-SHA256,
           ChaCha20Poly1305  . . . . . . . . . . . . . . . . . . . .  52
       C.2.1.  Base Setup Information  . . . . . . . . . . . . . . .  52
       C.2.2.  PSK Setup Information . . . . . . . . . . . . . . . .  55
     C.3.  DHKEM(P-256, HKDF-SHA256), HKDF-SHA256, AES-128-GCM . . .  58
       C.3.1.  Base Setup Information  . . . . . . . . . . . . . . .  58
       C.3.2.  PSK Setup Information . . . . . . . . . . . . . . . .  61
     C.4.  DHKEM(P-256, HKDF-SHA256), HKDF-SHA512, AES-128-GCM . . .  64
       C.4.1.  Base Setup Information  . . . . . . . . . . . . . . .  64
       C.4.2.  PSK Setup Information . . . . . . . . . . . . . . . .  67
     C.5.  DHKEM(P-256, HKDF-SHA256), HKDF-SHA256,
           ChaCha20Poly1305  . . . . . . . . . . . . . . . . . . . .  70
       C.5.1.  Base Setup Information  . . . . . . . . . . . . . . .  70
       C.5.2.  PSK Setup Information . . . . . . . . . . . . . . . .  73
     C.6.  DHKEM(P-521, HKDF-SHA512), HKDF-SHA512, AES-256-GCM . . .  76
       C.6.1.  Base Setup Information  . . . . . . . . . . . . . . .  76
       C.6.2.  PSK Setup Information . . . . . . . . . . . . . . . .  79




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     C.7.  DHKEM(X25519, HKDF-SHA256), HKDF-SHA256, Export-Only
           AEAD  . . . . . . . . . . . . . . . . . . . . . . . . . .  82
       C.7.1.  Base Setup Information  . . . . . . . . . . . . . . .  82
       C.7.2.  PSK Setup Information . . . . . . . . . . . . . . . .  84
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  85

1.  Introduction

   Encryption schemes that combine asymmetric and symmetric algorithms
   have been specified and practiced since the early days of public key
   cryptography, e.g., [RFC1421].  Combining the two yields the key
   management advantages of asymmetric cryptography and the performance
   benefits of symmetric cryptography.  The traditional combination has
   been "encrypt the symmetric key with the public key."  "Hybrid"
   public key encryption (HPKE) schemes, specified here, take a
   different approach: "generate the symmetric key and its encapsulation
   with the public key."  Specifically, encrypted messages convey a
   shared secret encapsulated with a public key scheme, along with one
   or more arbitrary-sized ciphertexts encrypted using that key.  This
   type of public key encryption has many applications in practice,
   including Messaging Layer Security [RFC9420], TLS Encrypted
   ClientHello [I-D.ietf-tls-esni], and Oblivious HTTP [RFC9458].

   Currently, there are numerous competing and non-interoperable
   standards and variants for hybrid encryption, mostly variants on the
   Elliptic Curve Integrated Encryption Scheme (ECIES), including ANSI
   X9.63 (ECIES) [ANSI], IEEE 1363a [IEEE1363], ISO/IEC 18033-2 [ISO],
   and SECG SEC 1 [SECG].  See [MAEA10] for a thorough comparison.  All
   these existing schemes have problems, e.g., because they rely on
   outdated primitives, lack proofs of indistinguishable (adaptive)
   chosen-ciphertext attack (IND-CCA2) security, or fail to provide test
   vectors.

   This document defines an HPKE scheme that provides a subset of the
   functions provided by the collection of schemes above but specified
   with sufficient clarity that they can be interoperably implemented.
   The HPKE construction defined herein is secure against (adaptive)
   chosen ciphertext attacks (IND-CCA2-secure) under classical
   assumptions about the underlying primitives [HPKEAnalysis]
   [ABHKLR20].  A summary of these analyses is in Section 9.1.

2.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.



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3.  Notation

   The following terms are used throughout this document to describe the
   operations, roles, and behaviors of HPKE:

   *  (skX, pkX): A key encapsulation mechanism (KEM) key pair used in
      role X, where X is one of S, R, or E as sender, recipient, and
      ephemeral, respectively; skX is the private key and pkX is the
      public key.

   *  pk(skX): The KEM public key corresponding to the KEM private key
      skX.

   *  Sender (S): Role of entity that sends an encrypted message.

   *  Recipient (R): Role of entity that receives an encrypted message.

   *  Ephemeral (E): Role of a fresh random value meant for one-time
      use.

   *  I2OSP(n, w): Convert non-negative integer n to a w-length, big-
      endian byte string, as described in [RFC8017].

   *  OS2IP(x): Convert byte string x to a non-negative integer, as
      described in [RFC8017], assuming big-endian byte order.

   *  concat(x0, ..., xN): Concatenation of byte strings. concat(0x01,
      0x0203, 0x040506) = 0x010203040506.

   *  lengthPrefixed(x): The two-byte length of the byte string x,
      concatenated with x itself.  (lengthPrefixed(x) =
      concat(I2OSP(len(x), 2), x)) It is an error to call this function
      with an x value that is more than 65535 bytes long.

   *  random(n): A pseudorandom byte string of length n bytes

   *  xor(a,b): XOR of byte strings; xor(0xF0F0, 0x1234) = 0xE2C4.  It
      is an error to call this function with two arguments of unequal
      length.

4.  Cryptographic Dependencies

   HPKE variants rely on the following primitives:

   *  A key encapsulation mechanism (KEM):

      -  GenerateKeyPair(): Randomized algorithm to generate a key pair
         (skX, pkX).



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      -  DeriveKeyPair(ikm): Deterministic algorithm to derive a key
         pair (skX, pkX) from the byte string ikm, where ikm is an
         arbitrary-length byte string (within the bounds in Table 4).
         The ikm input SHOULD have at least Nsk bytes of entropy.

      -  SerializePublicKey(pkX): Produce a byte string of length Npk
         encoding the public key pkX.

      -  DeserializePublicKey(pkXm): Parse a byte string of length Npk
         to recover a public key.  This function can raise a
         DeserializeError error upon pkXm deserialization failure.

      -  Encap(pkR): Randomized algorithm to generate an ephemeral,
         fixed-length shared secret and a fixed-length encapsulation of
         that secret (also known as the KEM ciphertext) that can be
         decapsulated by the holder of the private key corresponding to
         pkR.  This function can raise an EncapError on encapsulation
         failure.

      -  Decap(enc, skR): Deterministic algorithm using the private key
         skR to recover the shared secret) from the encapsulated secret
         enc.  This function can raise a DecapError on decapsulation
         failure.

      -  Nsecret: The length in bytes of a KEM shared secret produced by
         this KEM.

      -  Nenc: The length in bytes of an encapsulated secret produced by
         this KEM.

      -  Npk: The length in bytes of an encoded public key for this KEM.

      -  Nsk: The length in bytes of an encoded private key for this
         KEM.

   *  A key derivation function (KDF) of one of the two following forms:

      -  A one-stage KDF:

         o  Derive(ikm, L): Derive an L-byte value from the input keying
            material ikm.

         o  Nh The security strength of the KDF, in bytes.

      -  A two-stage KDF:






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         o  Extract(salt, ikm): Extract a pseudorandom key of fixed
            length Nh bytes from input keying material ikm and an
            optional byte string salt.

         o  Expand(prk, info, L): Expand a pseudorandom key prk using
            optional string info into L bytes of output keying material.

         o  Nh: The output size of the Extract() function in bytes.

   *  An AEAD encryption algorithm [RFC5116]:

      -  Seal(key, nonce, aad, pt): Encrypt and authenticate plaintext
         pt with associated data aad using symmetric key key and nonce
         nonce, yielding ciphertext and tag ct.  This function can raise
         a MessageLimitReachedError upon failure.

      -  Open(key, nonce, aad, ct): Decrypt ciphertext and tag ct using
         associated data aad with symmetric key key and nonce nonce,
         returning plaintext message pt.  This function can raise an
         OpenError or MessageLimitReachedError upon failure.

      -  Nk: The length in bytes of a key for this algorithm.

      -  Nn: The length in bytes of a nonce for this algorithm.

      -  Nt: The length in bytes of the authentication tag for this
         algorithm.

   Beyond the above, a KEM MAY also expose the following functions,
   whose behavior is detailed in Section 7.1.2:

   *  SerializePrivateKey(skX): Produce a byte string of length Nsk
      encoding the private key skX.

   *  DeserializePrivateKey(skXm): Parse a byte string of length Nsk to
      recover a private key.  This function can raise a DeserializeError
      error upon skXm deserialization failure.

   A _ciphersuite_ is a triple (KEM, KDF, AEAD) containing a choice of
   algorithm for each primitive.

   A set of algorithm identifiers for concrete instantiations of these
   primitives is provided in Section 7.  Algorithm identifier values are
   two bytes long.







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   The notation pk(skX), depending on its use and the KEM and its
   implementation, is either the computation of the public key using the
   private key, or just syntax expressing the retrieval of the public
   key, assuming it is stored along with the private key object.

   The following functions are defined to facilitate domain separation
   of KDF calls as well as context binding:

   # For use with one-stage KDFs
   def LabeledDerive(ikm, label, context, L):
     labeled_ikm = concat(
       ikm,
       "HPKE-v1",
       suite_id,
       lengthPrefixed(label),
       I2OSP(L, 2)
       context,
     )
     return Derive(labeled_ikm, L)

   # For use with two-stage KDFs
   def LabeledExtract(salt, label, ikm):
     labeled_ikm = concat("HPKE-v1", suite_id, label, ikm)
     return Extract(salt, labeled_ikm)

   def LabeledExpand(prk, label, info, L):
     labeled_info = concat(I2OSP(L, 2), "HPKE-v1", suite_id,
                           label, info)
     return Expand(prk, labeled_info, L)

   The value of suite_id depends on where the KDF is used; it is assumed
   implicit from the implementation and not passed as a parameter.  If
   used inside a KEM algorithm, suite_id MUST start with "KEM" and
   identify this KEM algorithm; if used in the remainder of HPKE, it
   MUST start with "HPKE" and identify the entire ciphersuite in use.
   See sections Section 4.1 and Section 5.1 for details.

   Certain functions have a different structure depending on whether a
   one-stage or two-stage KDF is being used.  For clarity, such
   functions will be described twice in this document, once with the
   suffix _OneStage and once with the suffix _TwoStage, representing the
   versions of the function to be used with a one-stage or two-stage
   KDF, respectively.  For example, the Foo function would be invoked by
   calling Foo_OneStage when using a one-stage KDF, and by calling
   Foo_TwoStage when using a two-stage KDF.






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4.1.  DH-Based KEM (DHKEM)

   Suppose we are given a KDF, and a Diffie-Hellman (DH) group providing
   the following operations:

   *  DH(skX, pkY): Perform a non-interactive Diffie-Hellman exchange
      using the private key skX and public key pkY to produce a Diffie-
      Hellman shared secret of length Ndh. This function can raise a
      ValidationError as described in Section 7.1.4.

   *  Ndh: The length in bytes of a Diffie-Hellman shared secret
      produced by DH().

   *  Nsk: The length in bytes of a Diffie-Hellman private key.

   Then we can construct a KEM that implements the interface defined in
   Section 4 called DHKEM(Group, KDF) in the following way, where Group
   denotes the Diffie-Hellman group and KDF denotes the KDF.  The
   function parameters pkR and pkS are deserialized public keys, and enc
   is a serialized public key.  Since encapsulated shared secrets are
   Diffie-Hellman public keys in this KEM algorithm, we use
   SerializePublicKey() and DeserializePublicKey() to encode and decode
   them, respectively.  Npk equals Nenc.  GenerateKeyPair() produces a
   key pair for the Diffie-Hellman group in use.  Section 7.1.3 contains
   the DeriveKeyPair() function specification for DHKEMs defined in this
   document.

























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   # For use with one-stage KDFs
   def ExtractAndExpand_OneStage(dh, kem_context):
     return LabeledDerive(dh, "shared_secret", kem_context, Nsecret)

   # For use with two-stage KDFs
   def ExtractAndExpand_TwoStage(dh, kem_context):
     eae_prk = LabeledExtract("", "eae_prk", dh)
     shared_secret = LabeledExpand(eae_prk, "shared_secret",
                                   kem_context, Nsecret)
     return shared_secret

   def Encap(pkR):
     skE, pkE = GenerateKeyPair()
     dh = DH(skE, pkR)
     enc = SerializePublicKey(pkE)

     pkRm = SerializePublicKey(pkR)
     kem_context = concat(enc, pkRm)

     shared_secret = ExtractAndExpand(dh, kem_context)
     return shared_secret, enc

   def Decap(enc, skR):
     pkE = DeserializePublicKey(enc)
     dh = DH(skR, pkE)

     pkRm = SerializePublicKey(pk(skR))
     kem_context = concat(enc, pkRm)

     shared_secret = ExtractAndExpand(dh, kem_context)
     return shared_secret

   The implicit suite_id value used within LabeledExtract,
   LabeledExpand, and LabeledDerive is defined as follows, where kem_id
   is defined in Section 7.1:

   suite_id = concat("KEM", I2OSP(kem_id, 2))

   The KDF used in DHKEM can be equal to or different from the KDF used
   in the remainder of HPKE, depending on the chosen variant.
   Implementations MUST make sure to use the constants (Nh) and function
   calls (LabeledExtract, LabeledExpand, and LabeledDerive) of the
   appropriate KDF when implementing DHKEM.  See Section 9.3 for a
   comment on the choice of a KDF for the remainder of HPKE, and
   Section 9.6 for the rationale of the labels.






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   For the variants of DHKEM defined in this document, the size Nsecret
   of the KEM shared secret is equal to the output length of the hash
   function underlying the KDF.  For P-256, P-384, and P-521, the size
   Ndh of the Diffie-Hellman shared secret is equal to 32, 48, and 66,
   respectively, corresponding to the x-coordinate of the resulting
   elliptic curve point [IEEE1363].  For X25519 and X448, the size Ndh
   is equal to 32 and 56, respectively (see [RFC7748], Section 5).

   Senders and recipients MUST validate KEM inputs and outputs as
   described in Section 7.1.

5.  Hybrid Public Key Encryption

   In this section, we define a few HPKE variants.  All variants take a
   recipient public key and a sequence of plaintexts pt and produce an
   encapsulated secret enc and a sequence of ciphertexts ct.  These
   outputs are constructed so that only the holder of skR can
   decapsulate the key from enc and decrypt the ciphertexts.  All the
   algorithms also take an info parameter that can be used to influence
   the generation of keys (e.g., to fold in identity information) and an
   aad parameter that provides additional authenticated data to the AEAD
   algorithm in use.

   In addition to the base case of encrypting to a public key, we
   include a variant that authenticates possession of a pre-shared key.
   The authenticated variant contributes additional keying material to
   the encryption operation.  The following one-byte values will be used
   to distinguish between modes:

                           +===========+=======+
                           | Mode      | Value |
                           +===========+=======+
                           | mode_base | 0x00  |
                           +-----------+-------+
                           | mode_psk  | 0x01  |
                           +-----------+-------+
                           | RESERVED  | 0x02  |
                           +-----------+-------+
                           | RESERVED  | 0x03  |
                           +-----------+-------+

                            Table 1: HPKE Modes

   (The values 0x02 and 0x03 were used in [RFC9180] to reflect
   additional variants which have been removed from this specification.)

   Both variants follow the same basic two-step pattern:




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   1.  Set up an encryption context that is shared between the sender
       and the recipient.

   2.  Use that context to encrypt or decrypt content.

   A _context_ is an implementation-specific structure that encodes the
   AEAD algorithm and key in use, and manages the nonces used so that
   the same nonce is not used with multiple plaintexts.  It also has an
   interface for exporting secret values, as described in Section 5.3.
   See Section 5.2 for a description of this structure and its
   interfaces.  HPKE decryption fails when the underlying AEAD
   decryption fails.

   The constructions described here presume that the relevant non-
   private parameters (enc, psk_id, etc.) are transported between the
   sender and the recipient by some application making use of HPKE.
   Moreover, a recipient with more than one public key needs some way of
   determining which of its public keys was used for the encapsulation
   operation.  As an example, applications may send this information
   alongside a ciphertext from the sender to the recipient.
   Specification of such a mechanism is left to the application.  See
   Section 10 for more details.

   The procedures described in this section are laid out in a Python-
   like pseudocode.  The algorithms in use are left implicit.

5.1.  Creating the Encryption Context

   The variants of HPKE defined in this document share a common key
   schedule that translates the protocol inputs into an encryption
   context.  The key schedule inputs are as follows:

   *  mode - A one-byte value indicating the HPKE mode, defined in
      Table 1.

   *  shared_secret - A KEM shared secret generated for this
      transaction.

   *  info - Application-supplied information (optional; default value
      "").

   *  psk - A pre-shared key (PSK) held by both the sender and the
      recipient (optional; default value "").

   *  psk_id - An identifier for the PSK (optional; default value "").

   Senders and recipients MUST validate KEM inputs and outputs as
   described in Section 7.1.



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   The info parameter used by HPKE is not related to the optional string
   info used by the LabeledExpand() or Expand() functions detailed in
   Section 4.

   The psk and psk_id parameters MUST appear together or not at all.
   That is, if a non-default value is provided for one of them, then the
   other MUST be set to a non-default value.  This requirement is
   encoded in VerifyPSKInputs() below.

   The psk, psk_id, and info parameters have maximum lengths that depend
   on the KDF itself, on the definition of LabeledExtract(), and on the
   constant labels used together with them.  See Section 7.2.1 for
   precise limits on these lengths.

   The key, base_nonce, and exporter_secret computed by the key schedule
   have the property that they are only known to the holder of the
   recipient private key, and the entity that used the KEM to generate
   shared_secret and enc.

   The HPKE algorithm identifiers, i.e., the KEM kem_id, KDF kdf_id, and
   AEAD aead_id 2-byte code points, as defined in Table 2, Table 3, and
   Table 5, respectively, are assumed implicit from the implementation
   and not passed as parameters.  The implicit suite_id value used
   within LabeledExtract, LabeledExpand, and LabeledDerive is defined
   based on them as follows:

   suite_id = concat(
     "HPKE",
     I2OSP(kem_id, 2),
     I2OSP(kdf_id, 2),
     I2OSP(aead_id, 2)
   )

   default_psk = ""
   default_psk_id = ""

   def VerifyPSKInputs(mode, psk, psk_id):
     got_psk = (psk != default_psk)
     got_psk_id = (psk_id != default_psk_id)
     if got_psk != got_psk_id:
       raise Exception("Inconsistent PSK inputs")

     if got_psk and mode == mode_base:
       raise Exception("PSK input provided when not needed")
     if (not got_psk) and mode == mode_psk:
       raise Exception("Missing required PSK input")

   # For use with a one-stage KDF



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   def CombineSecrets_OneStage(mode, shared_secret, info, psk, psk_id):
     secrets = concat(
       lengthPrefixed(psk),
       lengthPrefixed(shared_secret),
     )
     context = concat(
       mode,
       lengthPrefixed(psk_id),
       lengthPrefixed(info),
     )

     secret = LabeledDerive(secrets, "secret", context, Nk + Nn + Nh)

     key = secret[:Nk]
     base_nonce = secret[Nk:(Nk + Nn)]
     exporter_secret = secret[(Nk + Nn):]

     return (key, base_nonce, exporter_secret)

   # For use with a two-stage KDF
   def CombineSecrets_TwoStage(mode, shared_secret, info, psk, psk_id):
     psk_id_hash = LabeledExtract("", "psk_id_hash", psk_id)
     info_hash = LabeledExtract("", "info_hash", info)
     key_schedule_context = concat(mode, psk_id_hash, info_hash)

     secret = LabeledExtract(shared_secret, "secret", psk)

     key = LabeledExpand(secret, "key", key_schedule_context, Nk)
     base_nonce = LabeledExpand(secret, "base_nonce",
                                key_schedule_context, Nn)
     exporter_secret = LabeledExpand(secret, "exp",
                                     key_schedule_context, Nh)

     return (key, base_nonce, exporter_secret)

   def KeySchedule<ROLE>(mode, shared_secret, info, psk, psk_id):
     VerifyPSKInputs(mode, psk, psk_id)

     key, base_nonce, exporter_secret =
       CombineSecrets(mode, shared_secret, info, psk, psk_id)

     return Context<ROLE>(key, base_nonce, 0, exporter_secret)









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   The ROLE template parameter is either S or R, depending on the role
   of sender or recipient, respectively.  The third parameter in the
   Context<ROLE> refers to the sequence number, that is initialised with
   a 0 value.  See Section 5.2 for a discussion of the key schedule
   output, including the role-specific Context structure and its API,
   and the usage of the sequence number.

   Note that the key_schedule_context construction in KeySchedule() is
   equivalent to serializing a structure of the following form in the
   TLS presentation syntax:

   struct {
       uint8 mode;
       opaque psk_id_hash[Nh];
       opaque info_hash[Nh];
   } KeyScheduleContext;

5.1.1.  Encryption to a Public Key

   The most basic function of an HPKE scheme is to enable encryption to
   the holder of a given KEM private key.  The SetupBaseS() and
   SetupBaseR() procedures establish contexts that can be used to
   encrypt and decrypt, respectively, for a given private key.

   The KEM shared secret is combined via the KDF with information
   describing the key exchange, as well as the explicit info parameter
   provided by the caller.

   The parameter pkR is a public key, and enc is an encapsulated KEM
   shared secret.

   def SetupBaseS(pkR, info):
     shared_secret, enc = Encap(pkR)
     return enc, KeyScheduleS(mode_base, shared_secret, info,
                              default_psk, default_psk_id)

   def SetupBaseR(enc, skR, info):
     shared_secret = Decap(enc, skR)
     return KeyScheduleR(mode_base, shared_secret, info,
                         default_psk, default_psk_id)











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5.1.2.  Authentication Using a Pre-Shared Key

   This variant extends the base mechanism by allowing the recipient to
   authenticate that the sender possessed a given PSK.  The PSK also
   improves confidentiality guarantees in certain adversary models, as
   described in more detail in Section 9.1.  We assume that both parties
   have been provisioned with both the PSK value psk and another byte
   string psk_id that is used to identify which PSK should be used.

   The primary difference from the base case is that the psk and psk_id
   values are used as ikm inputs to the KDF (instead of using the empty
   string).

   The PSK MUST have at least 32 bytes of entropy and SHOULD be of
   length Nh bytes or longer.  See Section 9.5 for a more detailed
   discussion.

  def SetupPSKS(pkR, info, psk, psk_id):
    shared_secret, enc = Encap(pkR)
    return enc, KeyScheduleS(mode_psk, shared_secret, info, psk, psk_id)

  def SetupPSKR(enc, skR, info, psk, psk_id):
    shared_secret = Decap(enc, skR)
    return KeyScheduleR(mode_psk, shared_secret, info, psk, psk_id)

5.2.  Encryption and Decryption

   HPKE allows multiple encryption operations to be done based on a
   given setup transaction.  Since the public key operations involved in
   setup are typically more expensive than symmetric encryption or
   decryption, this allows applications to amortize the cost of the
   public key operations, reducing the overall overhead.

   In order to avoid nonce reuse, however, this encryption must be
   stateful.  Each of the setup procedures above produces a role-
   specific context object that stores the AEAD and secret export
   parameters.  The AEAD parameters consist of:

   *  The AEAD algorithm in use

   *  A secret key

   *  A base nonce base_nonce

   *  A sequence number (initially 0)

   The secret export parameters consist of:




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   *  The HPKE ciphersuite in use and

   *  An exporter_secret used for the secret export interface (see
      Section 5.3)

   All these parameters except the AEAD sequence number are constant.
   The sequence number provides nonce uniqueness: The nonce used for
   each encryption or decryption operation is the result of XORing
   base_nonce with the current sequence number, encoded as a big-endian
   integer of the same length as base_nonce.  Implementations MAY use a
   sequence number that is shorter than the nonce length (padding on the
   left with zero), but MUST raise an error if the sequence number
   overflows.  The AEAD algorithm produces ciphertext that is Nt bytes
   longer than the plaintext.  Nt = 16 for AEAD algorithms defined in
   this document.

   Encryption is unidirectional from sender to recipient.  The sender's
   context can encrypt a plaintext pt with associated data aad as
   follows:

   def ContextS.Seal(aad, pt):
     ct = Seal(self.key, self.ComputeNonce(self.seq), aad, pt)
     self.IncrementSeq()
     return ct

   The recipient's context can decrypt a ciphertext ct with associated
   data aad as follows:

   def ContextR.Open(aad, ct):
     pt = Open(self.key, self.ComputeNonce(self.seq), aad, ct)
     if pt == OpenError:
       raise OpenError
     self.IncrementSeq()
     return pt

   Each encryption or decryption operation increments the sequence
   number for the context in use.  The per-message nonce and sequence
   number increment details are as follows:

   def Context<ROLE>.ComputeNonce(seq):
     seq_bytes = I2OSP(seq, Nn)
     return xor(self.base_nonce, seq_bytes)

   def Context<ROLE>.IncrementSeq():
     if self.seq >= (1 << (8*Nn)) - 1:
       raise MessageLimitReachedError
     self.seq += 1




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   The sender's context MUST NOT be used for decryption.  Similarly, the
   recipient's context MUST NOT be used for encryption.  Higher-level
   protocols reusing the HPKE key exchange for more general purposes can
   derive separate keying material as needed using use the secret export
   interface; see Section 5.3 and Section 9.8 for more details.

   It is up to the application to ensure that encryptions and
   decryptions are done in the proper sequence, so that encryption and
   decryption nonces align.  If ContextS.Seal() or ContextR.Open() would
   cause the seq parameter to overflow, then the implementation MUST
   fail with an error.  (In the pseudocode above,
   Context<ROLE>.IncrementSeq() fails with an error when seq overflows,
   which causes ContextS.Seal() and ContextR.Open() to fail
   accordingly.)  Note that the internal Seal() and Open() calls inside
   correspond to the context's AEAD algorithm.

5.3.  Secret Export

   HPKE provides an interface for exporting secrets from the encryption
   context using a variable-length pseudorandom function (PRF).  This
   interface takes as input a context string exporter_context and a
   desired length L in bytes, and produces a secret derived from the
   internal exporter secret using the corresponding KDF Expand function.
   For the KDFs defined in this specification, L has a maximum value of
   255*Nh.  Future specifications that define new KDFs MUST specify a
   bound for L.

   The exporter_context parameter has a maximum length that depends on
   the KDF itself, on the definition of LabeledExpand(), and on the
   constant labels used together with them.  See Section 7.2.1 for
   precise limits on this length.

   # For use with a one-stage KDF
   def Context.Export_OneStage(exporter_context, L):
     return LabeledDerive(self.exporter_secret, "sec",
                          exporter_context, L)

   # For use with a two-stage KDF
   def Context.Export_TwoStage(exporter_context, L):
     return LabeledExpand(self.exporter_secret, "sec",
                          exporter_context, L)

   Applications that do not use the encryption API in Section 5.2 can
   use the export-only AEAD ID 0xFFFF when computing the key schedule.
   Such applications can avoid computing the key and base_nonce values
   in the key schedule, as they are not used by the Export interface
   described above.




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   Unlike the similar TLS 1.3 exporter interface (see Section 7.5 of
   [RFC8446]), the HPKE export interface does not provide replay
   protection.  While the resulting secret will only be known to the
   sender and recipient, a replayed encapsulated secret enc will produce
   an identical context, and thus the same exported secrets.  In
   particular, applications MUST NOT use exported secrets unless it is
   safe for the same exported values to be used multiple times.  For
   example, applications MUST NOT use an exported secret to derive a
   (key, nonce) pair for AEAD encryption (as suggested in Section 9.8 of
   [RFC9180]), since reuse of a (key, nonce) pair harms security in most
   AEAD algorithms.  In such cases, applications SHOULD incorporate a
   fresh recipient-provided nonce when deriving values from an export
   context, as discussed in Section 4.4 of [RFC9458] and Section 9.8.

6.  Single-Shot APIs

6.1.  Encryption and Decryption

   In many cases, applications encrypt only a single message to a
   recipient's public key.  This section provides templates for HPKE
   APIs that implement stateless "single-shot" encryption and decryption
   using APIs specified in Section 5.1 and Section 5.2:

   def Seal<MODE>(pkR, info, aad, pt, ...):
     enc, ctx = Setup<MODE>S(pkR, info, ...)
     ct = ctx.Seal(aad, pt)
     return enc, ct

   def Open<MODE>(enc, skR, info, aad, ct, ...):
     ctx = Setup<MODE>R(enc, skR, info, ...)
     return ctx.Open(aad, ct)

   The MODE template parameter is either Base or PSK.  The optional
   parameters indicated by "..." depend on MODE and may be empty.  For
   example, SetupBase() has no additional parameters.  SealPSK() and
   OpenPSK() would be implemented as follows:

   def SealPSK(pkR, info, aad, pt, psk, psk_id):
     enc, ctx = SetupPSKS(pkR, info, psk, psk_id)
     ct = ctx.Seal(aad, pt)
     return enc, ct

   def OpenPSK(enc, skR, info, aad, ct, psk, psk_id):
     ctx = SetupPSKR(enc, skR, info, psk, psk_id)
     return ctx.Open(aad, ct)






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6.2.  Secret Export

   Applications may also want to derive a secret known only to a given
   recipient.  This section provides templates for HPKE APIs that
   implement stateless "single-shot" secret export using APIs specified
   in Section 5.3:

   def SendExport<MODE>(pkR, info, exporter_context, L, ...):
     enc, ctx = Setup<MODE>S(pkR, info, ...)
     exported = ctx.Export(exporter_context, L)
     return enc, exported

   def ReceiveExport<MODE>(enc, skR, info, exporter_context, L, ...):
     ctx = Setup<MODE>R(enc, skR, info, ...)
     return ctx.Export(exporter_context, L)

   As in Section 6.1, the MODE template parameter is either Base or PSK.
   The optional parameters indicated by "..." depend on MODE and may be
   empty.

   Secrets exported using this single-shot API face the same replay
   risks discussed in Section 5.3.  Usage of exported secrets needs to
   be limited as described in that section.

7.  Algorithm Identifiers

   This section lists algorithm identifiers suitable for different HPKE
   configurations.  Future specifications may introduce new KEM, KDF,
   and AEAD algorithm identifiers and retain the security guarantees
   presented in this document provided they adhere to the security
   requirements in Section 9.2, Section 9.3, and Section 9.4,
   respectively.

7.1.  Key Encapsulation Mechanisms (KEMs)

   +======+===============+=========+====+===+===+====+===============+
   |Value | KEM           | Nsecret |Nenc|Npk|Nsk|Auth| Reference     |
   +======+===============+=========+====+===+===+====+===============+
   |0x0000| Reserved      | N/A     |N/A |N/A|N/A|yes | RFC 9180      |
   +------+---------------+---------+----+---+---+----+---------------+
   |0x0010| DHKEM(P-256,  | 32      |65  |65 |32 |yes | [NISTCurves], |
   |      | HKDF-SHA256)  |         |    |   |   |    | [RFC5869]     |
   +------+---------------+---------+----+---+---+----+---------------+
   |0x0011| DHKEM(P-384,  | 48      |97  |97 |48 |yes | [NISTCurves], |
   |      | HKDF-SHA384)  |         |    |   |   |    | [RFC5869]     |
   +------+---------------+---------+----+---+---+----+---------------+
   |0x0012| DHKEM(P-521,  | 64      |133 |133|66 |yes | [NISTCurves], |
   |      | HKDF-SHA512)  |         |    |   |   |    | [RFC5869]     |



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   +------+---------------+---------+----+---+---+----+---------------+
   |0x0020| DHKEM(X25519, | 32      |32  |32 |32 |yes | [RFC7748],    |
   |      | HKDF-SHA256)  |         |    |   |   |    | [RFC5869]     |
   +------+---------------+---------+----+---+---+----+---------------+
   |0x0021| DHKEM(X448,   | 64      |56  |56 |56 |yes | [RFC7748],    |
   |      | HKDF-SHA512)  |         |    |   |   |    | [RFC5869]     |
   +------+---------------+---------+----+---+---+----+---------------+

                             Table 2: KEM IDs

   The Auth column indicates if the KEM algorithm provides the
   AuthEncap()/AuthDecap() interface defined in [RFC9180].

7.1.1.  SerializePublicKey and DeserializePublicKey

   For P-256, P-384, and P-521, the SerializePublicKey() function of the
   KEM performs the uncompressed Elliptic-Curve-Point-to-Octet-String
   conversion according to [SECG].  DeserializePublicKey() performs the
   uncompressed Octet-String-to-Elliptic-Curve-Point conversion.

   For X25519 and X448, the SerializePublicKey() and
   DeserializePublicKey() functions are the identity function, since
   these curves already use fixed-length byte strings for public keys.

   Some deserialized public keys MUST be validated before they can be
   used.  See Section 7.1.4 for specifics.

7.1.2.  SerializePrivateKey and DeserializePrivateKey

   As per [SECG], P-256, P-384, and P-521 private keys are field
   elements in the scalar field of the curve being used.  For this
   section, and for Section 7.1.3, it is assumed that implementors of
   ECDH over these curves use an integer representation of private keys
   that is compatible with the OS2IP() function.

   For P-256, P-384, and P-521, the SerializePrivateKey() function of
   the KEM performs the Field-Element-to-Octet-String conversion
   according to [SECG].  If the private key is an integer outside the
   range [0, order-1], where order is the order of the curve being used,
   the private key MUST be reduced to its representative in [0, order-1]
   before being serialized.  DeserializePrivateKey() performs the Octet-
   String-to-Field-Element conversion according to [SECG].









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   For X25519 and X448, private keys are identical to their byte string
   representation, so little processing has to be done.  The
   SerializePrivateKey() function MUST clamp its output and the
   DeserializePrivateKey() function MUST clamp its input, where
   _clamping_ refers to the bitwise operations performed on k in the
   decodeScalar25519() and decodeScalar448() functions defined in
   Section 5 of [RFC7748].

   To catch invalid keys early on, implementors of DHKEMs SHOULD check
   that deserialized private keys are not equivalent to 0 (mod order),
   where order is the order of the DH group.  Note that this property is
   trivially true for X25519 and X448 groups, since clamped values can
   never be 0 (mod order).

7.1.3.  DeriveKeyPair

   The keys that DeriveKeyPair() produces have only as much entropy as
   the provided input keying material.  For a given KEM, the ikm
   parameter given to DeriveKeyPair() SHOULD have length at least Nsk,
   and SHOULD have at least Nsk bytes of entropy.

   All invocations of KDF functions (such as LabeledExtract or
   LabeledExpand) in any DHKEM's DeriveKeyPair() function use the
   DHKEM's associated KDF (as opposed to the ciphersuite's KDF).

   For P-256, P-384, and P-521, the DeriveKeyPair() function of the KEM
   performs rejection sampling over field elements:
























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   # For use with a one-stage KDF
   def DeriveCandidate_OneStage(ikm, counter):
     return LabeledDerive(ikm, "candidate", I2OSP(counter, 1), Nsk)

   # For use with a two-stage KDF
   def DeriveCandidate_TwoStage(ikm, counter):
     # Note: dkp_prk may be derived once and cached
     dkp_prk = LabeledExtract("", "dkp_prk", ikm)
     return LabeledExpand(dkp_prk, "candidate",
                             I2OSP(counter, 1), Nsk)

   def DeriveKeyPair(ikm):
     sk = 0
     counter = 0
     while sk == 0 or sk >= order:
       if counter > 255:
         raise DeriveKeyPairError
       bytes = DeriveCandidate(ikm, counter)
       bytes[0] = bytes[0] & bitmask
       sk = OS2IP(bytes)
       counter = counter + 1
     return (sk, pk(sk))

   order is the order of the curve being used (see Section D.1.2 of
   [NISTCurves]), and is listed below for completeness.

   P-256:
   0xffffffff00000000ffffffffffffffffbce6faada7179e84f3b9cac2fc632551

   P-384:
   0xffffffffffffffffffffffffffffffffffffffffffffffffc7634d81f4372ddf
     581a0db248b0a77aecec196accc52973

   P-521:
   0x01ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
     fa51868783bf2f966b7fcc0148f709a5d03bb5c9b8899c47aebb6fb71e91386409

   bitmask is defined to be 0xFF for P-256 and P-384, and 0x01 for
   P-521.  The precise likelihood of DeriveKeyPair() failing with
   DeriveKeyPairError depends on the group being used, but it is
   negligibly small in all cases.  See Section 8.2 for information about
   dealing with such failures.

   For X25519 and X448, the DeriveKeyPair() function applies a KDF to
   the input:






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   # For use with a one-stage KDF
   def DeriveKeyPair_OneStage(ikm):
     sk = LabeledDerive(ikm, "sk", "", Nsk)
     return (sk, pk(sk))

   # For use with a two-stage KDF
   def DeriveKeyPair_TwoStage(ikm):
     dkp_prk = LabeledExtract("", "dkp_prk", ikm)
     sk = LabeledExpand(dkp_prk, "sk", "", Nsk)
     return (sk, pk(sk))

   The suite_id used implicitly in LabeledExtract() and LabeledExpand()
   for DeriveKeyPair(ikm) is derived from the KEM identifier of the
   DHKEM in use (see Section 7.1), that is, based on the type of key
   pair been generated for that DHKEM type.

   For all of the above instances of DHKEM, the GenerateKeyPair can be
   implemented as DeriveKeyPair(random(Nsk)).

7.1.4.  Validation of Inputs and Outputs

   The following public keys are subject to validation if the group
   requires public key validation: the sender MUST validate the
   recipient's public key pkR; the recipient MUST validate the ephemeral
   public key pkE.  Validation failure yields a ValidationError.

   For P-256, P-384 and P-521, senders and recipients MUST perform
   partial public key validation on all public key inputs, as defined in
   Section 5.6.2.3.4 of [keyagreement].  This includes checking that the
   coordinates are in the correct range, that the point is on the curve,
   and that the point is not the point at infinity.  Additionally,
   senders and recipients MUST ensure the Diffie-Hellman shared secret
   is not the point at infinity.

   For X25519 and X448, public keys and Diffie-Hellman outputs MUST be
   validated as described in [RFC7748].  In particular, recipients MUST
   check whether the Diffie-Hellman shared secret is the all-zero value
   and abort if so.

7.1.5.  Future KEMs

   Section 9.2 lists security requirements on a KEM used within HPKE.

   A KEM algorithm may support different encoding algorithms, with
   different output lengths, for KEM public keys.  Such KEM algorithms
   MUST specify only one encoding algorithm whose output length is Npk.





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7.2.  Key Derivation Functions (KDFs)

          +========+=============+=====+===========+===========+
          | Value  | KDF         | Nh  | Two-Stage | Reference |
          +========+=============+=====+===========+===========+
          | 0x0000 | Reserved    | N/A | N/A       | RFC 9180  |
          +--------+-------------+-----+-----------+-----------+
          | 0x0001 | HKDF-SHA256 | 32  | Y         | [RFC5869] |
          +--------+-------------+-----+-----------+-----------+
          | 0x0002 | HKDF-SHA384 | 48  | Y         | [RFC5869] |
          +--------+-------------+-----+-----------+-----------+
          | 0x0003 | HKDF-SHA512 | 64  | Y         | [RFC5869] |
          +--------+-------------+-----+-----------+-----------+

                             Table 3: KDF IDs

7.2.1.  Input Length Restrictions

   For one-stage KDFs, there is length limit of 65,535 bytes for the
   psk, psk_id, info fields.  This limitation arises because these
   fields are all prefixed with a two-byte length when being used as KDF
   inputs.  There is no inherent length limitation on exporter_context.
   If a one-stage KDF has an input length limit, then implementations
   MUST limit the length of exporter_context accordingly, so that the
   LabeledDerive call in Context.Export does not overflow the input
   length limit.

   For two-stage KDFs, this document defines LabeledExtract() and
   LabeledExpand() based on the KDFs listed above.  These functions add
   prefixes to their respective inputs ikm and info before calling the
   KDF's Extract() and Expand() functions.  This leads to a reduction of
   the maximum input length that is available for the inputs psk,
   psk_id, info, exporter_context, ikm, i.e., the variable-length
   parameters provided by HPKE applications.  The following table lists
   the maximum allowed lengths of these parameters for the KDFs defined
   in this document, as inclusive bounds in bytes:















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    +==================+==============+===============+===============+
    | Input            | HKDF-SHA256  | HKDF-SHA384   | HKDF-SHA512   |
    +==================+==============+===============+===============+
    | psk              | 2^{61} - 88  | 2^{125} - 152 | 2^{125} - 152 |
    +------------------+--------------+---------------+---------------+
    | psk_id           | 2^{61} - 93  | 2^{125} - 157 | 2^{125} - 157 |
    +------------------+--------------+---------------+---------------+
    | info             | 2^{61} - 91  | 2^{125} - 155 | 2^{125} - 155 |
    +------------------+--------------+---------------+---------------+
    | exporter_context | 2^{61} - 120 | 2^{125} - 200 | 2^{125} - 216 |
    +------------------+--------------+---------------+---------------+
    | ikm              | 2^{61} - 84  | 2^{125} - 148 | 2^{125} - 148 |
    | (DeriveKeyPair)  |              |               |               |
    +------------------+--------------+---------------+---------------+

                     Table 4: Application Input Limits

   This shows that the limits are only marginally smaller than the
   maximum input length of the underlying hash function; these limits
   are large and unlikely to be reached in practical applications.
   Future specifications that define new KDFs MUST specify bounds for
   these variable-length parameters.

   Since the above bounds are larger than any values used in practice,
   it may be useful for implementations to impose a lower limit on the
   values they will accept (for example, to avoid dynamic allocations).
   Implementations SHOULD set such a limit to be no less than maximum
   Nsk size for a KEM supported by the implementation.  For an
   implementation that supports all of the KEMs in this document, the
   limit would be 66 bytes, which is the Nsk value for DHKEM(P-521,
   HKDF-SHA512).

   The values for psk, psk_id, info, and ikm, which are inputs to
   LabeledExtract(), were computed with the following expression:

   max_size_hash_input - Nb - size_version_label -
       size_suite_id - size_input_label

   The value for exporter_context, which is an input to LabeledExpand(),
   was computed with the following expression:

   max_size_hash_input - Nb - Nh - size_version_label -
       size_suite_id - size_input_label - 2 - 1

   In these equations, max_size_hash_input is the maximum input length
   of the underlying hash function in bytes, Nb is the block size of the
   underlying hash function in bytes, size_version_label is the size of
   "HPKE-v1" in bytes and equals 7, size_suite_id is the size of the



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   suite_id in bytes and equals 5 for DHKEM (relevant for ikm) and 10
   for the remainder of HPKE (relevant for psk, psk_id, info, and
   exporter_context), and size_input_label is the size in bytes of the
   label used as parameter to LabeledExtract() or LabeledExpand(), the
   maximum of which is 13 across all labels in this document.

7.3.  Authenticated Encryption with Associated Data (AEAD) Functions

        +========+==================+=====+=====+=====+===========+
        | Value  | AEAD             | Nk  | Nn  | Nt  | Reference |
        +========+==================+=====+=====+=====+===========+
        | 0x0000 | Reserved         | N/A | N/A | N/A | RFC 9180  |
        +--------+------------------+-----+-----+-----+-----------+
        | 0x0001 | AES-128-GCM      | 16  | 12  | 16  | [GCM]     |
        +--------+------------------+-----+-----+-----+-----------+
        | 0x0002 | AES-256-GCM      | 32  | 12  | 16  | [GCM]     |
        +--------+------------------+-----+-----+-----+-----------+
        | 0x0003 | ChaCha20Poly1305 | 32  | 12  | 16  | [RFC8439] |
        +--------+------------------+-----+-----+-----+-----------+
        | 0xFFFF | Export-only      | N/A | N/A | N/A | RFC 9180  |
        +--------+------------------+-----+-----+-----+-----------+

                             Table 5: AEAD IDs

   The 0xFFFF AEAD ID is reserved for applications that only use the
   Export interface; see Section 5.3 for more details.

8.  API Considerations

   This section documents considerations for interfaces to
   implementations of HPKE.  This includes error handling considerations
   and recommendations that improve interoperability when HPKE is used
   in applications.

8.1.  Auxiliary Authenticated Application Information

   HPKE has two places at which applications can specify auxiliary
   authenticated information: (1) during context construction via the
   Setup info parameter, and (2) during Context operations, i.e., with
   the aad parameter for Open() and Seal(), and the exporter_context
   parameter for Export().  Application information applicable to
   multiple operations on a single Context should use the Setup info
   parameter.  This avoids redundantly processing this information for
   each Context operation.  In contrast, application information that
   varies on a per-message basis should be specified via the Context
   APIs (Seal(), Open(), or Export()).





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   Applications that only use the single-shot APIs described in
   Section 6 should use the Setup info parameter for specifying
   auxiliary authenticated information.  Implementations which only
   expose single-shot APIs should not allow applications to use both
   Setup info and Context aad or exporter_context auxiliary information
   parameters.

8.2.  Errors

   The high-level, public HPKE APIs specified in this document are all
   fallible.  These include the Setup functions and all encryption
   context functions.  For example, Decap() can fail if the encapsulated
   secret enc is invalid, and Open() may fail if ciphertext decryption
   fails.  The explicit errors generated throughout this specification,
   along with the conditions that lead to each error, are as follows:

   *  ValidationError: KEM input or output validation failure;
      Section 4.1.

   *  DeserializeError: Public or private key deserialization failure;
      Section 4.

   *  EncapError: Encap() failure; Section 4.

   *  DecapError: Decap() failure; Section 4.

   *  OpenError: Context AEAD Open() failure; Section 4 and Section 5.2.

   *  MessageLimitReachedError: Context AEAD sequence number overflow;
      Section 4 and Section 5.2.

   *  DeriveKeyPairError: Key pair derivation failure; Section 7.1.3.

   Implicit errors may also occur.  As an example, certain classes of
   failures, e.g., malformed recipient public keys, may not yield
   explicit errors.  For example, for the DHKEM variant described in
   this specification, the Encap() algorithm fails when given an invalid
   recipient public key.  However, other KEM algorithms may not have an
   efficient algorithm for verifying the validity of public keys.  As a
   result, an equivalent error may not manifest until AEAD decryption at
   the recipient.

   The errors in this document are meant as a guide for implementors.
   They are not an exhaustive list of all the errors an implementation
   might emit.  For example, future KEMs might have internal failure
   cases, or an implementation might run out of memory.





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   How these errors are expressed in an API or handled by applications
   is an implementation-specific detail.  For example, some
   implementations may abort or panic upon a DeriveKeyPairError failure
   given that it only occurs with negligible probability, whereas other
   implementations may retry the failed DeriveKeyPair operation.  See
   Section 7.1.3 for more information.  As another example, some
   implementations of the DHKEM specified in this document may choose to
   transform ValidationError from DH() into an EncapError or DecapError
   from Encap() or Decap(), respectively, whereas others may choose to
   raise ValidationError unmodified.

   Applications using HPKE APIs should not assume that the errors here
   are complete, nor should they assume certain classes of errors will
   always manifest the same way for all ciphersuites.  For example, the
   DHKEM specified in this document will emit a DeserializationError or
   ValidationError if a KEM public key is invalid.  However, a new KEM
   might not have an efficient algorithm for determining whether or not
   a public key is valid.  In this case, an invalid public key might
   instead yield an OpenError when trying to decrypt a ciphertext.

9.  Security Considerations

9.1.  Security Properties

   HPKE has several security goals, depending on the mode of operation,
   against active and adaptive attackers that can compromise partial
   secrets of senders and recipients.  The desired security goals are
   detailed below:

   *  Message secrecy: Confidentiality of the sender's messages against
      chosen ciphertext attacks

   *  Export key secrecy: Indistinguishability of each export secret
      from a uniformly random bitstring of equal length, i.e.,
      Context.Export is a variable-length PRF

   *  Sender authentication: Proof of sender origin for the PSK mode

   These security goals are expected to hold for any honest sender and
   honest recipient keys, as well as if the honest sender and honest
   recipient keys are the same.

   HPKE mitigates malleability problems (called benign malleability
   [SECG]) in prior public key encryption standards based on ECIES by
   including all public keys in the context of the key schedule.






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   HPKE does not provide forward secrecy with respect to recipient
   compromise.  In the Base mode, the secrecy properties are only
   expected to hold if the recipient private key skR is not compromised
   at any point in time.  In the PSK mode, the secrecy properties are
   expected to hold if the recipient private key skR and the pre-shared
   key are not both compromised at any point in time.  See Section 9.7
   for more details.

   Besides forward secrecy and key-compromise impersonation, which are
   highlighted in this section because of their particular cryptographic
   importance, HPKE has other non-goals that are described in
   Section 9.7: no tolerance of message reordering or loss, no downgrade
   or replay prevention, no hiding of the plaintext length, and no
   protection against bad ephemeral randomness.  Section 9.7 suggests
   application-level mitigations for some of them.

9.1.1.  Computational Analysis

   It is shown in [CS01] that a hybrid public key encryption scheme of
   essentially the same form as the Base mode described here is IND-
   CCA2-secure as long as the underlying KEM and AEAD schemes are IND-
   CCA2-secure.  Moreover, it is shown in [HHK06] that IND-CCA2 security
   of the KEM and the data encapsulation mechanism are necessary
   conditions to achieve IND-CCA2 security for hybrid public key
   encryption.  The main difference between the scheme proposed in
   [CS01] and the Base mode in this document (both named HPKE) is that
   we interpose some KDF calls between the KEM and the AEAD.  Analyzing
   the HPKE Base mode instantiation in this document therefore requires
   verifying that the additional KDF calls do not cause the IND-CCA2
   property to fail, as well as verifying the additional export key
   secrecy property.

   A preliminary computational analysis of all HPKE modes has been done
   in [HPKEAnalysis], indicating asymptotic security for the case where
   the KEM is DHKEM, the AEAD is any IND-CPA-secure and INT-CTXT-secure
   scheme, and the DH group and KDF satisfy the following conditions:

   *  DH group: The gap Diffie-Hellman (GDH) problem is hard in the
      appropriate subgroup [GAP].

   *  Extract() and Expand(): Extract() can be modeled as a random
      oracle.  Expand() can be modeled as a pseudorandom function,
      wherein the first argument is the key.

   In particular, the KDFs and DH groups defined in this document (see
   Section 7.2 and Section 7.1) satisfy these properties when used as
   specified.  The analysis in [HPKEAnalysis] demonstrates that under
   these constraints, HPKE continues to provide IND-CCA2 security, and



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   provides the additional properties noted above.  Also, the analysis
   confirms the expected properties hold under the different key
   compromise cases mentioned above.  The analysis considers a sender
   that sends one message using the encryption context, and additionally
   exports two independent secrets using the secret export interface.

   The table below summarizes the main results from [HPKEAnalysis].  N/A
   means that a property does not apply for the given mode, whereas Y
   means the given mode satisfies the property.

          +=========+==============+=============+==============+
          | Variant | Message Sec. | Export Sec. | Sender Auth. |
          +=========+==============+=============+==============+
          | Base    |      Y       |      Y      |     N/A      |
          +---------+--------------+-------------+--------------+
          | PSK     |      Y       |      Y      |      Y       |
          +---------+--------------+-------------+--------------+

                                  Table 6

   If non-DH-based KEMs are to be used with HPKE, further analysis will
   be necessary to prove their security.  The results from [CS01]
   provide some indication that any IND-CCA2-secure KEM will suffice
   here, but are not conclusive given the differences in the schemes.

9.1.2.  Post-Quantum Security

   All of [CS01], [HPKEAnalysis], and [ABHKLR20] are premised on
   classical security models and assumptions, and do not consider
   adversaries capable of quantum computation.  A full proof of post-
   quantum security would need to take appropriate security models and
   assumptions into account, in addition to simply using a post-quantum
   KEM.

   In future work, the analysis from [ABHKLR20] can be extended to cover
   HPKE's other modes and desired security properties.  The hybrid
   quantum-resistance property described above, which is achieved by
   using the PSK mode, is not proven in [HPKEAnalysis] because this
   analysis requires the random oracle model; in a quantum setting, this
   model needs adaption to, for example, the quantum random oracle
   model.

9.2.  Security Requirements on a KEM Used within HPKE

   A KEM used within HPKE MUST allow HPKE to satisfy its desired
   security properties described in Section 9.1.  Section 9.6 lists
   requirements concerning domain separation.




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   In particular, the KEM shared secret MUST be a uniformly random byte
   string of length Nsecret.  This means, for instance, that it would
   not be sufficient if the KEM shared secret is only uniformly random
   as an element of some set prior to its encoding as a byte string.

9.2.1.  Encap/Decap Interface

   As mentioned in Section 9, [CS01] provides some indications that if
   the KEM's Encap()/Decap() interface (which is used in the Base and
   PSK modes) is IND-CCA2-secure, HPKE is able to satisfy its desired
   security properties.  An appropriate definition of IND-CCA2 security
   for KEMs can be found in [CS01] and [BHK09].

9.2.2.  KEM Key Reuse

   An ikm input to DeriveKeyPair() (Section 7.1.3) MUST NOT be reused
   elsewhere, in particular not with DeriveKeyPair() of a different KEM.

   Since a KEM key pair belonging to a sender or recipient works with
   all modes, it can be used with multiple modes in parallel.  HPKE is
   constructed to be secure in such settings due to domain separation
   using the suite_id variable.  However, there is no formal proof of
   security at the time of writing for using multiple modes in parallel;
   [HPKEAnalysis] and [ABHKLR20] only analyze isolated modes.

9.3.  Security Requirements on a KDF

   The choice of the KDF for HPKE SHOULD be made based on the security
   level provided by the KEM and, if applicable, by the PSK.  The KDF
   SHOULD at least have the security level of the KEM and SHOULD at
   least have the security level provided by the PSK.

9.4.  Security Requirements on an AEAD

   All AEADs MUST be IND-CCA2-secure, as is currently true for all AEADs
   listed in Section 7.3.

9.5.  Pre-Shared Key Recommendations

   In the PSK modes, the PSK MUST have at least 32 bytes of entropy and
   SHOULD be of length Nh bytes or longer.  Using a PSK longer than 32
   bytes but shorter than Nh bytes is permitted.

   HPKE is specified to use HKDF as its key derivation function.  HKDF
   is not designed to slow down dictionary attacks (see [RFC5869]).
   Thus, HPKE's PSK mechanism is not suitable for use with a low-entropy
   password as the PSK: In scenarios in which the adversary knows the
   KEM shared secret shared_secret and has access to an oracle that



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   distinguishes between a good and a wrong PSK, it can perform PSK-
   recovering attacks.  This oracle can be the decryption operation on a
   captured HPKE ciphertext or any other recipient behavior that is
   observably different when using a wrong PSK.  The adversary knows the
   KEM shared secret shared_secret if it knows all KEM private keys of
   one participant.  In the PSK mode, this is trivially the case if the
   adversary acts as the sender.

   To recover a lower entropy PSK, an attacker in this scenario can
   trivially perform a dictionary attack.  Given a set S of possible PSK
   values, the attacker generates an HPKE ciphertext for each value in
   S, and submits the resulting ciphertexts to the oracle to learn which
   PSK is being used by the recipient.  Further, because HPKE uses AEAD
   schemes that are not key-committing, an attacker can mount a
   partitioning oracle attack [LGR20] that can recover the PSK from a
   set of S possible PSK values, with |S| = m*k, in roughly m + log k
   queries to the oracle using ciphertexts of length proportional to k,
   the maximum message length in blocks.  (Applying the multi-collision
   algorithm from [LGR20] requires a small adaptation to the algorithm
   wherein the appropriate nonce is computed for each candidate key.
   This modification adds one call to HKDF per key.  The number of
   partitioning oracle queries remains unchanged.)  As a result, the PSK
   must therefore be chosen with sufficient entropy so that m + log k is
   prohibitive for attackers (e.g., 2^128).  Future specifications can
   define new AEAD algorithms that are key-committing.

9.6.  Domain Separation

   HPKE allows combining a DHKEM variant DHKEM(Group, KDF') and a KDF
   such that both KDFs are instantiated by the same KDF.  By design, the
   calls to Extract() and Expand() inside DHKEM and the remainder of
   HPKE use separate input domains.  This justifies modeling them as
   independent functions even if instantiated by the same KDF.  This
   domain separation between DHKEM and the remainder of HPKE is achieved
   by using prefix-free sets of suite_id values in LabeledExtract(),
   LabeledExpand(), and LabeledDerive (KEM... in DHKEM and HPKE... in
   the remainder of HPKE).  Recall that a set is prefix-free if no
   element is a prefix of another within the set.

   Separation between uses of the one-stage and two-stage KDFs is
   ensured by the inclusion of the suite_id in LabeledExtract,
   LabeledExpand, and LabeledDerive.

   Future KEM instantiations MUST ensure, should Extract(), Expand(),
   and/or Derive() be used internally, that they can be modeled as
   functions independent from the invocations of these functions in the
   remainder of HPKE.  One way to ensure this is by using
   LabeledExtract() / LabeledExpand() / LabeledDerive() functions with a



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   suite_id as defined in Section 4, which will ensure input domain
   separation, as outlined above.  Particular attention needs to be paid
   if the KEM directly invokes functions that are used internally in
   HPKE's Extract() or Expand(), such as Hash() and HMAC() in the case
   of HKDF.  It MUST be ensured that inputs to these invocations cannot
   collide with inputs to the internal invocations of these functions
   inside Extract() or Expand().  In HPKE's KeySchedule() this is
   avoided by using Extract() instead of Hash() on the arbitrary-length
   inputs info and psk_id.

   The string literal "HPKE-v1" used in LabeledExtract() /
   LabeledExpand() / LabeledDerive() ensures that any secrets derived in
   HPKE are bound to the scheme's name and version, even when possibly
   derived from the same Diffie-Hellman or KEM shared secret as in
   another scheme or version.

9.7.  Application Embedding and Non-Goals

   HPKE is designed to be a fairly low-level mechanism.  As a result, it
   assumes that certain properties are provided by the application in
   which HPKE is embedded and leaves certain security properties to be
   provided by other mechanisms.  Otherwise said, certain properties are
   out-of-scope for HPKE.

9.7.1.  Message Order and Message Loss

   The primary requirement that HPKE imposes on applications is the
   requirement that ciphertexts MUST be presented to ContextR.Open() in
   the same order in which they were generated by ContextS.Seal().  When
   the single-shot API is used (see Section 6), this is trivially true
   (since there is only ever one ciphertext.  Applications that allow
   for multiple invocations of Open() / Seal() on the same context MUST
   enforce the ordering property described above.

   Ordering requirements of this character are usually fulfilled by
   providing a sequence number in the framing of encrypted messages.
   Whatever information is used to determine the ordering of HPKE-
   encrypted messages SHOULD be included in the AAD passed to
   ContextS.Seal() and ContextR.Open().  The specifics of this scheme
   are up to the application.

   HPKE is not tolerant of lost messages.  Applications MUST be able to
   detect when a message has been lost.  When an unrecoverable loss is
   detected, the application MUST discard any associated HPKE context.







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9.7.2.  Downgrade Prevention

   HPKE assumes that the sender and recipient agree on what algorithms
   to use.  Depending on how these algorithms are negotiated, it may be
   possible for an intermediary to force the two parties to use
   suboptimal algorithms.

9.7.3.  Replay Protection

   The requirement that ciphertexts be presented to the ContextR.Open()
   function in the same order they were generated by ContextS.Seal()
   provides a degree of replay protection within a stream of ciphertexts
   resulting from a given context.  HPKE provides no other replay
   protection.

   While a sender can guarantee the uniqueness of HPKE ciphertexts, a
   recipient might receive the same ciphertext multiple times.  Unless
   the recipient takes particular care to guarantee that replay is
   impossible, such as tracking all enc values that are received, this
   can result in multiple contexts that have the same shared secret.
   This is particularly relevant for exported secrets.

   If an attacker can cause a recipient to re-use an enc value, any
   exported secrets will be the same as in the initial transaction.
   While the exported values are still known only to the sender and
   recipient (not the replay attacker), such replay can allow the
   attacker to cause the recipient to re-use the exported values.

   Consider the following scenario, in which B is using the recipient-
   to-sender encryption described as an example in Section 9.8 of
   [RFC9180]:




















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   B->A: pk

   A:    enc1, ctx = SetupBaseS(pk)
         ct1 = ctx.seal(aad, pt)
   A->B: enc1, ct1

   B:    ctx = SetupBaseR(sk, enc1)
         key, nonce = ctx.export(...)
         ct2 = AEAD.seal(key, nonce, aad2, pt2)
   B->A: ct2

   X->B: enc1, ct1 [replay of previously sent values]

   B:    ctx = SetupBaseR(sk, enc)
         key, nonce = ctx.export(...)
         ct3 = AEAD.seal(key, nonce, aad3, pt3)
   B->X: ct3

            Figure 1: Attacker-triggered nonce reuse via replay

   In this scenario, if aad2 is different from aad3 or pt2 is different
   from pt3 (for example, due to the use of a timestamp in either
   field), then the ciphertexts ct2 and ct3 will represent encryptions
   of different values with the same (key, nonce) pair -- a nonce reuse
   condition that can completely break the authenticated encryption
   guarantees for several AEAD algorithms, including those defined in
   Section 7.3.

   In order to avoid such risks, applications SHOULD incorporate a fresh
   recipient-provided nonce when deriving values from an export context,
   as discussed in Section 4.4 of [RFC9458] and Section 9.8.

9.7.4.  Forward Secrecy

   HPKE ciphertexts are not forward secret with respect to recipient
   compromise in any mode.  This means that compromise of long-term
   recipient secrets allows an attacker to decrypt past ciphertexts
   encrypted under said secrets.  This is because only long-term secrets
   are used on the side of the recipient.

   HPKE ciphertexts are forward secret with respect to sender compromise
   in all modes.  This is because ephemeral randomness is used on the
   sender's side, which is supposed to be erased directly after
   computation of the KEM shared secret and ciphertext.







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9.7.5.  Bad Ephemeral Randomness

   If the randomness used for KEM encapsulation is bad -- i.e., of low
   entropy or compromised because of a broken or subverted random number
   generator -- the confidentiality guarantees of HPKE degrade
   significantly.  In Base mode, confidentiality guarantees can be lost
   completely; in the other modes, at least forward secrecy with respect
   to sender compromise can be lost completely.

   Such a situation could also lead to the reuse of the same KEM shared
   secret and thus to the reuse of same key-nonce pairs for the AEAD.
   The AEADs specified in this document are not secure in case of nonce
   reuse.  This attack vector is particularly relevant in the
   authenticated mode because knowledge of the ephemeral randomness is
   not enough to derive shared_secret in these modes.

   One way for applications to mitigate the impacts of bad ephemeral
   randomness is to combine ephemeral randomness with a local long-term
   secret that has been generated securely, as described in [RFC8937].

9.7.6.  Hiding Plaintext Length

   AEAD ciphertexts produced by HPKE do not hide the plaintext length.
   Applications requiring this level of privacy should use a suitable
   padding mechanism.  See [I-D.ietf-tls-esni] and [RFC8467] for
   examples of protocol-specific padding policies.

9.8.  Bidirectional Encryption

   As discussed in Section 5.2, HPKE encryption is unidirectional from
   sender to recipient.  Applications that require bidirectional
   encryption can derive necessary keying material with the secret
   export interface Section 5.3.  The type and length of such keying
   material depends on the application use case.

   As an example, if an application needs AEAD encryption from the
   recipient to the sender, it can derive a key and nonce from the
   corresponding HPKE context as follows:

   def EncryptResponse(context, enc, response_aad, response_pt):
     secret = context.Export("[application] response", Nh)
     response_nonce = random(Nh)
     salt = concat(enc, response_nonce)
     prk = Extract(salt, secret)
     aead_key = Expand(prk, "key", Nk)
     aead_nonce = Expand(prk, "nonce", Nn)
     ct = Seal(aead_key, aead_nonce, response_aad, response_pt)
     return (response_nonce, ct)



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   This example mechanism differs from the example mechanism in
   [RFC9180] by incorporating a per-transaction random value
   response_nonce.  Because HPKE does not provide replay protection, the
   mechanism in [RFC9180] enabled an attacker to trigger reuse of a
   (key, nonce) pair by replaying an HPKE message under certain
   application circumstances.  Incorporating per-transaction entropy
   ensures that the key and nonce used in AEAD encryption will be
   distinct for every invocation of the mechanism.

   In this context, HPKE's limitations with regard to sender
   authentication become limits on recipient authentication.  In
   particular, in the Base mode, there is no authentication of the
   remote party at all.

9.9.  Metadata Protection

   The PSK mode of HPKE requires that the recipient know what key
   material to use for the sender.  This can be signaled in applications
   by sending the PSK ID (psk_id above) and/or the sender's public key
   (pkS).  However, these values themselves might be considered
   sensitive, since, in a given application context, they might identify
   the sender.

   An application that wishes to protect these metadata values without
   requiring further provisioning of keys can use an additional instance
   of HPKE, using the unauthenticated Base mode.  Where the application
   might have sent (psk_id, enc, ciphertext) before, it would now send
   (enc2, ciphertext2, enc, ciphertext), where (enc2, ciphertext2)
   represent the encryption of the psk_id value.

   The cost of this approach is an additional KEM operation each for the
   sender and the recipient.  A potential lower-cost approach (involving
   only symmetric operations) would be available if the nonce-protection
   schemes in [BNT19] could be extended to cover other metadata.
   However, this construction would require further analysis.

10.  Message Encoding

   This document does not specify a wire format encoding for HPKE
   messages.  Applications that adopt HPKE must therefore specify an
   unambiguous encoding mechanism that includes, minimally: the
   encapsulated secret enc, ciphertext value(s) (and order if there are
   multiple), and any info values that are not implicit.  One example of
   a non-implicit value is the recipient public key used for
   encapsulation, which may be needed if a recipient has more than one
   public key.





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   The AEAD interface used in this document is based on [RFC5116], which
   produces and consumes a single ciphertext value.  As discussed in
   [RFC5116], this ciphertext value contains the encrypted plaintext as
   well as any authentication data, encoded in a manner described by the
   individual AEAD scheme.  Some implementations are not structured in
   this way, instead providing a separate ciphertext and authentication
   tag.  When such AEAD implementations are used in HPKE
   implementations, the HPKE implementation must combine these inputs
   into a single ciphertext value within Seal() and parse them out
   within Open(), where the parsing details are defined by the AEAD
   scheme.  For example, with the AES-GCM schemes specified in this
   document, the GCM authentication tag is placed in the last Nt bytes
   of the ciphertext output.

11.  IANA Considerations

   IANA created three new registries as requested in Section 11 of
   [RFC9180]:

   *  HPKE KEM Identifiers

   *  HPKE KDF Identifiers

   *  HPKE AEAD Identifiers

   All these registries are under "Hybrid Public Key Encryption", and
   administered under a Specification Required policy [RFC8126].

   This document requests that entries in these registries referring to
   RFC 9180 be updated to refer to this document.

11.1.  KEM Identifiers

   The "HPKE KEM Identifiers" registry lists identifiers for key
   encapsulation algorithms defined for use with HPKE.  These
   identifiers are two-byte values, so the maximum possible value is
   0xFFFF = 65535.

   Template:

   *  Value: The two-byte identifier for the algorithm

   *  KEM: The name of the algorithm

   *  Nsecret: The length in bytes of a KEM shared secret produced by
      the algorithm





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   *  Nenc: The length in bytes of an encoded encapsulated secret
      produced by the algorithm

   *  Npk: The length in bytes of an encoded public key for the
      algorithm

   *  Nsk: The length in bytes of an encoded private key for the
      algorithm

   *  Auth: A boolean indicating if this algorithm provides the
      AuthEncap()/AuthDecap() interface

   *  Reference: Where this algorithm is defined

   Initial contents: Provided in Table 2

11.2.  KDF Identifiers

   The "HPKE KDF Identifiers" registry lists identifiers for key
   derivation functions defined for use with HPKE.  These identifiers
   are two-byte values, so the maximum possible value is 0xFFFF = 65535.

   Template:

   *  Value: The two-byte identifier for the algorithm

   *  KDF: The name of the algorithm

   *  Nh: The output size of the Extract function in bytes

   *  Reference: Where this algorithm is defined

   Initial contents: Provided in Table 3

11.3.  AEAD Identifiers

   The "HPKE AEAD Identifiers" registry lists identifiers for
   authenticated encryption with associated data (AEAD) algorithms
   defined for use with HPKE.  These identifiers are two-byte values, so
   the maximum possible value is 0xFFFF = 65535.

   Template:

   *  Value: The two-byte identifier for the algorithm

   *  AEAD: The name of the algorithm

   *  Nk: The length in bytes of a key for this algorithm



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   *  Nn: The length in bytes of a nonce for this algorithm

   *  Nt: The length in bytes of an authentication tag for this
      algorithm

   *  Reference: Where this algorithm is defined

   Initial contents: Provided in Table 5

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC5116]  McGrew, D., "An Interface and Algorithms for Authenticated
              Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
              <https://www.rfc-editor.org/rfc/rfc5116>.

   [RFC8017]  Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
              "PKCS #1: RSA Cryptography Specifications Version 2.2",
              RFC 8017, DOI 10.17487/RFC8017, November 2016,
              <https://www.rfc-editor.org/rfc/rfc8017>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/rfc/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC9458]  Thomson, M. and C. A. Wood, "Oblivious HTTP", RFC 9458,
              DOI 10.17487/RFC9458, January 2024,
              <https://www.rfc-editor.org/rfc/rfc9458>.

12.2.  Informative References

   [ABHKLR20] Alwen, J., Blanchet, B., Hauck, E., Kiltz, E., Lipp, B.,
              and D. Riepel, "Analysing the HPKE Standard", 2020,
              <https://eprint.iacr.org/2020/1499>.






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   [ANSI]     American National Standards Institute, "ANSI X9.63 Public
              Key Cryptography for the Financial Services Industry --
              Key Agreement and Key Transport Using Elliptic Curve
              Cryptography", 2001.

   [BHK09]    Mihir Bellare, Dennis Hofheinz, and Eike Kiltz,
              "Subtleties in the Definition of IND-CCA: When and How
              Should Challenge-Decryption be Disallowed?", 2009,
              <https://eprint.iacr.org/2009/418>.

   [BNT19]    Bellare, M., Ng, R., and B. Tackmann, "Nonces Are Noticed:
              AEAD Revisited", 2019,
              <http://dx.doi.org/10.1007/978-3-030-26948-7_9>.

   [CS01]     Cramer, R. and V. Shoup, "Design and Analysis of Practical
              Public-Key Encryption Schemes Secure against Adaptive
              Chosen Ciphertext Attack", 2001,
              <https://eprint.iacr.org/2001/108>.

   [FIPS202]  "SHA-3 standard :: permutation-based hash and extendable-
              output functions", National Institute of Standards and
              Technology (U.S.), DOI 10.6028/nist.fips.202, 2015,
              <https://doi.org/10.6028/nist.fips.202>.

   [GAP]      Okamoto, T. and D. Pointcheval, "The Gap-Problems - a New
              Class of Problems for the Security of Cryptographic
              Schemes", ISBN 978-3-540-44586-9, 2001,
              <https://link.springer.com/content/
              pdf/10.1007/3-540-44586-2_8.pdf>.

   [GCM]      Dworkin, M., "Recommendation for block cipher modes of
              operation :: GaloisCounter Mode (GCM) and GMAC", National
              Institute of Standards and Technology,
              DOI 10.6028/nist.sp.800-38d, 2007,
              <https://doi.org/10.6028/nist.sp.800-38d>.

   [HHK06]    Herranz, J., Hofheinz, D., and E. Kiltz, "Some
              (in)sufficient conditions for secure hybrid encryption",
              2006, <https://eprint.iacr.org/2006/265>.

   [HPKEAnalysis]
              Lipp, B., "An Analysis of Hybrid Public Key Encryption",
              2020, <https://eprint.iacr.org/2020/243>.








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   [I-D.ietf-tls-esni]
              Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS
              Encrypted Client Hello", Work in Progress, Internet-Draft,
              draft-ietf-tls-esni-25, 14 June 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              esni-25>.

   [IEEE1363] Institute of Electrical and Electronics Engineers, "IEEE
              1363a, Standard Specifications for Public Key Cryptography
              - Amendment 1 -- Additional Techniques"", 2004.

   [IMB]      Diffie, W., Van Oorschot, P., and M. Wiener,
              "Authentication and authenticated key exchanges", Springer
              Science and Business Media LLC, Designs, Codes and
              Cryptography vol. 2, no. 2, pp. 107-125,
              DOI 10.1007/bf00124891, June 1992,
              <https://doi.org/10.1007/bf00124891>.

   [ISO]      International Organization for Standardization /
              International Electrotechnical Commission, "ISO/IEC
              18033-2, Information Technology - Security Techniques -
              Encryption Algorithms - Part 2 -- Asymmetric Ciphers",
              2006.

   [keyagreement]
              Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R.
              Davis, "Recommendation for pair-wise key-establishment
              schemes using discrete logarithm cryptography", National
              Institute of Standards and Technology,
              DOI 10.6028/nist.sp.800-56ar3, April 2018,
              <https://doi.org/10.6028/nist.sp.800-56ar3>.

   [LGR20]    Len, J., Grubbs, P., and T. Ristenpart, "Partitioning
              Oracle Attacks", 2021,
              <https://eprint.iacr.org/2020/1491>.

   [MAEA10]   Gayoso Martinez, V., Hernandez Alvarez, F., Hernandez
              Encinas, L., and C. Sanchez Avila, "A Comparison of the
              Standardized Versions of ECIES", 2010,
              <https://ieeexplore.ieee.org/abstract/document/5604194/>.

   [NISTCurves]
              "Digital signature standard (DSS)", National Institute of
              Standards and Technology (U.S.),
              DOI 10.6028/nist.fips.186-4, 2013,
              <https://doi.org/10.6028/nist.fips.186-4>.





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   [RFC1421]  Linn, J., "Privacy Enhancement for Internet Electronic
              Mail: Part I: Message Encryption and Authentication
              Procedures", RFC 1421, DOI 10.17487/RFC1421, February
              1993, <https://www.rfc-editor.org/rfc/rfc1421>.

   [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
              Key Derivation Function (HKDF)", RFC 5869,
              DOI 10.17487/RFC5869, May 2010,
              <https://www.rfc-editor.org/rfc/rfc5869>.

   [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
              for Security", RFC 7748, DOI 10.17487/RFC7748, January
              2016, <https://www.rfc-editor.org/rfc/rfc7748>.

   [RFC8439]  Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
              Protocols", RFC 8439, DOI 10.17487/RFC8439, June 2018,
              <https://www.rfc-editor.org/rfc/rfc8439>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/rfc/rfc8446>.

   [RFC8467]  Mayrhofer, A., "Padding Policies for Extension Mechanisms
              for DNS (EDNS(0))", RFC 8467, DOI 10.17487/RFC8467,
              October 2018, <https://www.rfc-editor.org/rfc/rfc8467>.

   [RFC8937]  Cremers, C., Garratt, L., Smyshlyaev, S., Sullivan, N.,
              and C. Wood, "Randomness Improvements for Security
              Protocols", RFC 8937, DOI 10.17487/RFC8937, October 2020,
              <https://www.rfc-editor.org/rfc/rfc8937>.

   [RFC9180]  Barnes, R., Bhargavan, K., Lipp, B., and C. Wood, "Hybrid
              Public Key Encryption", RFC 9180, DOI 10.17487/RFC9180,
              February 2022, <https://www.rfc-editor.org/rfc/rfc9180>.

   [RFC9420]  Barnes, R., Beurdouche, B., Robert, R., Millican, J.,
              Omara, E., and K. Cohn-Gordon, "The Messaging Layer
              Security (MLS) Protocol", RFC 9420, DOI 10.17487/RFC9420,
              July 2023, <https://www.rfc-editor.org/rfc/rfc9420>.

   [SECG]     "Elliptic Curve Cryptography, Standards for Efficient
              Cryptography Group, ver. 2", 2009,
              <https://secg.org/sec1-v2.pdf>.








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   [SigncryptionDZ10]
              "Practical Signcryption", Springer Berlin Heidelberg,
              Information Security and Cryptography,
              DOI 10.1007/978-3-540-89411-7, ISBN ["9783540894094",
              "9783540894117"], 2010,
              <https://doi.org/10.1007/978-3-540-89411-7>.

   [TestVectors]
              "HPKE Test Vectors", 2021, <https://github.com/cfrg/draft-
              irtf-cfrg-
              hpke/blob/5f503c564da00b0687b3de75f1dfbdfc4079ad31/test-
              vectors.json>.

Appendix A.  Differences from RFC 9180

   This specification is intended to be backwards-compatible with RFC
   9180, in the sense that any behavior specified in both this document
   and RFC 9180 should specify identical behavior for any functionality
   that they both specify.

   Within that constraint, the following list summarizes the major
   changes from RFC 9180:

   *  Incorporated fixes for all valid errata on RFC 9180.

   *  Updated the IANA considerations refer to existing registries.

   *  Added a framework for single-stage KDFs.

   *  Removed the Auth and AuthPSK modes.

   *  Extended the discussion of replay to conver considerations related
      to exported secrets.

Appendix B.  Acknowledgements

   The authors would like to thank Joël Alwen, Jean-Philippe Aumasson,
   David Benjamin, Benjamin Beurdouche, Bruno Blanchet, Frank Denis,
   Stephen Farrell, Scott Fluhrer, Eduard Hauck, Scott Hollenbeck, Kevin
   Jacobs, Burt Kaliski, Eike Kiltz, Julia Len, John Mattsson,
   Christopher Patton, Doreen Riepel, Raphael Robert, Michael Rosenberg,
   Michael Scott, Martin Thomson, Steven Valdez, Riad Wahby, and other
   contributors in the CFRG for helpful feedback that greatly improved
   this document.







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Appendix C.  Test Vectors

   Each section below contains test vectors for a single HPKE
   ciphersuite and contains the following values:

   1.  Configuration information and private key material: This includes
       the mode, info string, HPKE ciphersuite identifiers (kem_id,
       kdf_id, aead_id), and all sender, recipient, and ephemeral key
       material.  For each role X, where X is one of S, R, or E, as
       sender, recipient, and ephemeral, respectively, key pairs are
       generated as (skX, pkX) = DeriveKeyPair(ikmX).  Each key pair
       (skX, pkX) is written in its serialized form, where skXm =
       SerializePrivateKey(skX) and pkXm = SerializePublicKey(pkX).  For
       applicable modes, the shared PSK and PSK identifier are also
       included.

   2.  Context creation intermediate values and outputs: This includes
       the KEM outputs enc and shared_secret used to create the context,
       along with intermediate values key_schedule_context and secret
       computed in the KeySchedule function in Section 5.1.  The outputs
       include the context values key, base_nonce, and exporter_secret.

   3.  Encryption test vectors: A fixed plaintext message is encrypted
       using different sequence numbers and AAD values using the context
       computed in (2).  Each test vector lists the sequence number and
       corresponding nonce computed with base_nonce, the plaintext
       message pt, AAD aad, and output ciphertext ct.

   4.  Export test vectors: Several exported values of the same length
       with differing context parameters are computed using the context
       computed in (2).  Each test vector lists the exporter_context,
       output length L, and resulting export value.

   These test vectors are also available in JSON format at
   [TestVectors].

C.1.  DHKEM(X25519, HKDF-SHA256), HKDF-SHA256, AES-128-GCM

C.1.1.  Base Setup Information












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   mode: 0
   kem_id: 32
   kdf_id: 1
   aead_id: 1
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   7268600d403fce431561aef583ee1613527cff655c1343f29812e66706df3234
   pkEm:
   37fda3567bdbd628e88668c3c8d7e97d1d1253b6d4ea6d44c150f741f1bf4431
   skEm:
   52c4a758a802cd8b936eceea314432798d5baf2d7e9235dc084ab1b9cfa2f736
   ikmR:
   6db9df30aa07dd42ee5e8181afdb977e538f5e1fec8a06223f33f7013e525037
   pkRm:
   3948cfe0ad1ddb695d780e59077195da6c56506b027329794ab02bca80815c4d
   skRm:
   4612c550263fc8ad58375df3f557aac531d26850903e55a9f23f21d8534e8ac8
   enc:
   37fda3567bdbd628e88668c3c8d7e97d1d1253b6d4ea6d44c150f741f1bf4431
   shared_secret:
   fe0e18c9f024ce43799ae393c7e8fe8fce9d218875e8227b0187c04e7d2ea1fc
   key_schedule_context: 00725611c9d98c07c03f60095cd32d400d8347d45ed670
   97bbad50fc56da742d07cb6cffde367bb0565ba28bb02c90744a20f5ef37f3052352
   6106f637abb05449
   secret:
   12fff91991e93b48de37e7daddb52981084bd8aa64289c3788471d9a9712f397
   key: 4531685d41d65f03dc48f6b8302c05b0
   base_nonce: 56d890e5accaaf011cff4b7d
   exporter_secret:
   45ff1c2e220db587171952c0592d5f5ebe103f1561a2614e38f2ffd47e99e3f8

C.1.1.1.  Encryptions



















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   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: 56d890e5accaaf011cff4b7d
   ct: f938558b5d72f1a23810b4be2ab4f84331acc02fc97babc53a52ae8218a355a9
   6d8770ac83d07bea87e13c512a

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: 56d890e5accaaf011cff4b7c
   ct: af2d7e9ac9ae7e270f46ba1f975be53c09f8d875bdc8535458c2494e8a6eab25
   1c03d0c22a56b8ca42c2063b84

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: 56d890e5accaaf011cff4b7f
   ct: 498dfcabd92e8acedc281e85af1cb4e3e31c7dc394a1ca20e173cb7251649158
   8d96a19ad4a683518973dcc180

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: 56d890e5accaaf011cff4b79
   ct: 583bd32bc67a5994bb8ceaca813d369bca7b2a42408cddef5e22f880b631215a
   09fc0012bc69fccaa251c0246d

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: 56d890e5accaaf011cff4b82
   ct: 7175db9717964058640a3a11fb9007941a5d1757fda1a6935c805c21af32505b
   f106deefec4a49ac38d71c9e0a

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: 56d890e5accaaf011cff4a7d
   ct: 957f9800542b0b8891badb026d79cc54597cb2d225b54c00c5238c25d05c30e3
   fbeda97d2e0e1aba483a2df9f2

C.1.1.2.  Exported Values








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   exporter_context:
   L: 32
   exported_value:
   3853fe2b4035195a573ffc53856e77058e15d9ea064de3e59f4961d0095250ee

   exporter_context: 00
   L: 32
   exported_value:
   2e8f0b54673c7029649d4eb9d5e33bf1872cf76d623ff164ac185da9e88c21a5

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   e9e43065102c3836401bed8c3c3c75ae46be1639869391d62c61f1ec7af54931

C.1.2.  PSK Setup Information



































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   mode: 1
   kem_id: 32
   kdf_id: 1
   aead_id: 1
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   78628c354e46f3e169bd231be7b2ff1c77aa302460a26dbfa15515684c00130b
   pkEm:
   0ad0950d9fb9588e59690b74f1237ecdf1d775cd60be2eca57af5a4b0471c91b
   skEm:
   463426a9ffb42bb17dbe6044b9abd1d4e4d95f9041cef0e99d7824eef2b6f588
   ikmR:
   d4a09d09f575fef425905d2ab396c1449141463f698f8efdb7accfaff8995098
   pkRm:
   9fed7e8c17387560e92cc6462a68049657246a09bfa8ade7aefe589672016366
   skRm:
   c5eb01eb457fe6c6f57577c5413b931550a162c71a03ac8d196babbd4e5ce0fd
   psk:
   0247fd33b913760fa1fa51e1892d9f307fbe65eb171e8132c2af18555a738b82
   psk_id: 456e6e796e20447572696e206172616e204d6f726961
   enc:
   0ad0950d9fb9588e59690b74f1237ecdf1d775cd60be2eca57af5a4b0471c91b
   shared_secret:
   727699f009ffe3c076315019c69648366b69171439bd7dd0807743bde76986cd
   key_schedule_context: 01e78d5cf6190d275863411ff5edd0dece5d39fa48e04e
   ec1ed9b71be34729d18ccb6cffde367bb0565ba28bb02c90744a20f5ef37f3052352
   6106f637abb05449
   secret:
   3728ab0b024b383b0381e432b47cced1496d2516957a76e2a9f5c8cb947afca4
   key: 15026dba546e3ae05836fc7de5a7bb26
   base_nonce: 9518635eba129d5ce0914555
   exporter_secret:
   3d76025dbbedc49448ec3f9080a1abab6b06e91c0b11ad23c912f043a0ee7655

C.1.2.1.  Encryptions
















Barnes, et al.             Expires 8 May 2026                  [Page 50]

Internet-Draft                    HPKE                     November 2025


   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: 9518635eba129d5ce0914555
   ct: e52c6fed7f758d0cf7145689f21bc1be6ec9ea097fef4e959440012f4feb73fb
   611b946199e681f4cfc34db8ea

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: 9518635eba129d5ce0914554
   ct: 49f3b19b28a9ea9f43e8c71204c00d4a490ee7f61387b6719db765e948123b45
   b61633ef059ba22cd62437c8ba

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: 9518635eba129d5ce0914557
   ct: 257ca6a08473dc851fde45afd598cc83e326ddd0abe1ef23baa3baa4dd8cde99
   fce2c1e8ce687b0b47ead1adc9

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: 9518635eba129d5ce0914551
   ct: a71d73a2cd8128fcccbd328b9684d70096e073b59b40b55e6419c9c68ae21069
   c847e2a70f5d8fb821ce3dfb1c

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: 9518635eba129d5ce09145aa
   ct: 55f84b030b7f7197f7d7d552365b6b932df5ec1abacd30241cb4bc4ccea27bd2
   b518766adfa0fb1b71170e9392

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: 9518635eba129d5ce0914455
   ct: c5bf246d4a790a12dcc9eed5eae525081e6fb541d5849e9ce8abd92a3bc15517
   76bea16b4a518f23e237c14b59

C.1.2.2.  Exported Values








Barnes, et al.             Expires 8 May 2026                  [Page 51]

Internet-Draft                    HPKE                     November 2025


   exporter_context:
   L: 32
   exported_value:
   dff17af354c8b41673567db6259fd6029967b4e1aad13023c2ae5df8f4f43bf6

   exporter_context: 00
   L: 32
   exported_value:
   6a847261d8207fe596befb52928463881ab493da345b10e1dcc645e3b94e2d95

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   8aff52b45a1be3a734bc7a41e20b4e055ad4c4d22104b0c20285a7c4302401cd

C.2.  DHKEM(X25519, HKDF-SHA256), HKDF-SHA256, ChaCha20Poly1305

C.2.1.  Base Setup Information

































Barnes, et al.             Expires 8 May 2026                  [Page 52]

Internet-Draft                    HPKE                     November 2025


   mode: 0
   kem_id: 32
   kdf_id: 1
   aead_id: 3
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   909a9b35d3dc4713a5e72a4da274b55d3d3821a37e5d099e74a647db583a904b
   pkEm:
   1afa08d3dec047a643885163f1180476fa7ddb54c6a8029ea33f95796bf2ac4a
   skEm:
   f4ec9b33b792c372c1d2c2063507b684ef925b8c75a42dbcbf57d63ccd381600
   ikmR:
   1ac01f181fdf9f352797655161c58b75c656a6cc2716dcb66372da835542e1df
   pkRm:
   4310ee97d88cc1f088a5576c77ab0cf5c3ac797f3d95139c6c84b5429c59662a
   skRm:
   8057991eef8f1f1af18f4a9491d16a1ce333f695d4db8e38da75975c4478e0fb
   enc:
   1afa08d3dec047a643885163f1180476fa7ddb54c6a8029ea33f95796bf2ac4a
   shared_secret:
   0bbe78490412b4bbea4812666f7916932b828bba79942424abb65244930d69a7
   key_schedule_context: 00431df6cd95e11ff49d7013563baf7f11588c75a6611e
   e2a4404a49306ae4cfc5b69c5718a60cc5876c358d3f7fc31ddb598503f67be58ea1
   e798c0bb19eb9796
   secret:
   5b9cd775e64b437a2335cf499361b2e0d5e444d5cb41a8a53336d8fe402282c6
   key:
   ad2744de8e17f4ebba575b3f5f5a8fa1f69c2a07f6e7500bc60ca6e3e3ec1c91
   base_nonce: 5c4d98150661b848853b547f
   exporter_secret:
   a3b010d4994890e2c6968a36f64470d3c824c8f5029942feb11e7a74b2921922

C.2.1.1.  Encryptions


















Barnes, et al.             Expires 8 May 2026                  [Page 53]

Internet-Draft                    HPKE                     November 2025


   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: 5c4d98150661b848853b547f
   ct: 1c5250d8034ec2b784ba2cfd69dbdb8af406cfe3ff938e131f0def8c8b60b4db
   21993c62ce81883d2dd1b51a28

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: 5c4d98150661b848853b547e
   ct: 6b53c051e4199c518de79594e1c4ab18b96f081549d45ce015be002090bb119e
   85285337cc95ba5f59992dc98c

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: 5c4d98150661b848853b547d
   ct: 71146bd6795ccc9c49ce25dda112a48f202ad220559502cef1f34271e0cb4b02
   b4f10ecac6f48c32f878fae86b

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: 5c4d98150661b848853b547b
   ct: 63357a2aa291f5a4e5f27db6baa2af8cf77427c7c1a909e0b37214dd47db122b
   b153495ff0b02e9e54a50dbe16

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: 5c4d98150661b848853b5480
   ct: 18ab939d63ddec9f6ac2b60d61d36a7375d2070c9b683861110757062c52b888
   0a5f6b3936da9cd6c23ef2a95c

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: 5c4d98150661b848853b557f
   ct: 7a4a13e9ef23978e2c520fd4d2e757514ae160cd0cd05e556ef692370ca53076
   214c0c40d4c728d6ed9e727a5b

C.2.1.2.  Exported Values








Barnes, et al.             Expires 8 May 2026                  [Page 54]

Internet-Draft                    HPKE                     November 2025


   exporter_context:
   L: 32
   exported_value:
   4bbd6243b8bb54cec311fac9df81841b6fd61f56538a775e7c80a9f40160606e

   exporter_context: 00
   L: 32
   exported_value:
   8c1df14732580e5501b00f82b10a1647b40713191b7c1240ac80e2b68808ba69

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   5acb09211139c43b3090489a9da433e8a30ee7188ba8b0a9a1ccf0c229283e53

C.2.2.  PSK Setup Information



































Barnes, et al.             Expires 8 May 2026                  [Page 55]

Internet-Draft                    HPKE                     November 2025


   mode: 1
   kem_id: 32
   kdf_id: 1
   aead_id: 3
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   35706a0b09fb26fb45c39c2f5079c709c7cf98e43afa973f14d88ece7e29c2e3
   pkEm:
   2261299c3f40a9afc133b969a97f05e95be2c514e54f3de26cbe5644ac735b04
   skEm:
   0c35fdf49df7aa01cd330049332c40411ebba36e0c718ebc3edf5845795f6321
   ikmR:
   26b923eade72941c8a85b09986cdfa3f1296852261adedc52d58d2930269812b
   pkRm:
   13640af826b722fc04feaa4de2f28fbd5ecc03623b317834e7ff4120dbe73062
   skRm:
   77d114e0212be51cb1d76fa99dd41cfd4d0166b08caa09074430a6c59ef17879
   psk:
   0247fd33b913760fa1fa51e1892d9f307fbe65eb171e8132c2af18555a738b82
   psk_id: 456e6e796e20447572696e206172616e204d6f726961
   enc:
   2261299c3f40a9afc133b969a97f05e95be2c514e54f3de26cbe5644ac735b04
   shared_secret:
   4be079c5e77779d0215b3f689595d59e3e9b0455d55662d1f3666ec606e50ea7
   key_schedule_context: 016870c4c76ca38ae43efbec0f2377d109499d7ce73f4a
   9e1ec37f21d3d063b97cb69c5718a60cc5876c358d3f7fc31ddb598503f67be58ea1
   e798c0bb19eb9796
   secret:
   16974354c497c9bd24c000ceed693779b604f1944975b18c442d373663f4a8cc
   key:
   600d2fdb0313a7e5c86a9ce9221cd95bed069862421744cfb4ab9d7203a9c019
   base_nonce: 112e0465562045b7368653e7
   exporter_secret:
   73b506dc8b6b4269027f80b0362def5cbb57ee50eed0c2873dac9181f453c5ac

C.2.2.1.  Encryptions















Barnes, et al.             Expires 8 May 2026                  [Page 56]

Internet-Draft                    HPKE                     November 2025


   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: 112e0465562045b7368653e7
   ct: 4a177f9c0d6f15cfdf533fb65bf84aecdc6ab16b8b85b4cf65a370e07fc1d78d
   28fb073214525276f4a89608ff

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: 112e0465562045b7368653e6
   ct: 5c3cabae2f0b3e124d8d864c116fd8f20f3f56fda988c3573b40b09997fd6c76
   9e77c8eda6cda4f947f5b704a8

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: 112e0465562045b7368653e5
   ct: 14958900b44bdae9cbe5a528bf933c5c990dbb8e282e6e495adf8205d19da9eb
   270e3a6f1e0613ab7e757962a4

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: 112e0465562045b7368653e3
   ct: c2a7bc09ddb853cf2effb6e8d058e346f7fe0fb3476528c80db6b698415c5f8c
   50b68a9a355609e96d2117f8d3

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: 112e0465562045b736865318
   ct: 2414d0788e4bc39a59a26d7bd5d78e111c317d44c37bd5a4c2a1235f2ddc2085
   c487d406490e75210c958724a7

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: 112e0465562045b7368652e7
   ct: c567ae1c3f0f75abe1dd9e4532b422600ed4a6e5b9484dafb1e43ab9f5fd662b
   28c00e2e81d3cde955dae7e218

C.2.2.2.  Exported Values








Barnes, et al.             Expires 8 May 2026                  [Page 57]

Internet-Draft                    HPKE                     November 2025


   exporter_context:
   L: 32
   exported_value:
   813c1bfc516c99076ae0f466671f0ba5ff244a41699f7b2417e4c59d46d39f40

   exporter_context: 00
   L: 32
   exported_value:
   2745cf3d5bb65c333658732954ee7af49eb895ce77f8022873a62a13c94cb4e1

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   ad40e3ae14f21c99bfdebc20ae14ab86f4ca2dc9a4799d200f43a25f99fa78ae

C.3.  DHKEM(P-256, HKDF-SHA256), HKDF-SHA256, AES-128-GCM

C.3.1.  Base Setup Information

































Barnes, et al.             Expires 8 May 2026                  [Page 58]

Internet-Draft                    HPKE                     November 2025


   mode: 0
   kem_id: 16
   kdf_id: 1
   aead_id: 1
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   4270e54ffd08d79d5928020af4686d8f6b7d35dbe470265f1f5aa22816ce860e
   pkEm: 04a92719c6195d5085104f469a8b9814d5838ff72b60501e2c4466e5e67b32
   5ac98536d7b61a1af4b78e5b7f951c0900be863c403ce65c9bfcb9382657222d18c4
   skEm:
   4995788ef4b9d6132b249ce59a77281493eb39af373d236a1fe415cb0c2d7beb
   ikmR:
   668b37171f1072f3cf12ea8a236a45df23fc13b82af3609ad1e354f6ef817550
   pkRm: 04fe8c19ce0905191ebc298a9245792531f26f0cece2460639e8bc39cb7f70
   6a826a779b4cf969b8a0e539c7f62fb3d30ad6aa8f80e30f1d128aafd68a2ce72ea0
   skRm:
   f3ce7fdae57e1a310d87f1ebbde6f328be0a99cdbcadf4d6589cf29de4b8ffd2
   enc: 04a92719c6195d5085104f469a8b9814d5838ff72b60501e2c4466e5e67b325
   ac98536d7b61a1af4b78e5b7f951c0900be863c403ce65c9bfcb9382657222d18c4
   shared_secret:
   c0d26aeab536609a572b07695d933b589dcf363ff9d93c93adea537aeabb8cb8
   key_schedule_context: 00b88d4e6d91759e65e87c470e8b9141113e9ad5f0c8ce
   efc1e088c82e6980500798e486f9c9c09c9b5c753ac72d6005de254c607d1b534ed1
   1d493ae1c1d9ac85
   secret:
   2eb7b6bf138f6b5aff857414a058a3f1750054a9ba1f72c2cf0684a6f20b10e1
   key: 868c066ef58aae6dc589b6cfdd18f97e
   base_nonce: 4e0bc5018beba4bf004cca59
   exporter_secret:
   14ad94af484a7ad3ef40e9f3be99ecc6fa9036df9d4920548424df127ee0d99f

C.3.1.1.  Encryptions



















Barnes, et al.             Expires 8 May 2026                  [Page 59]

Internet-Draft                    HPKE                     November 2025


   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: 4e0bc5018beba4bf004cca59
   ct: 5ad590bb8baa577f8619db35a36311226a896e7342a6d836d8b7bcd2f20b6c7f
   9076ac232e3ab2523f39513434

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: 4e0bc5018beba4bf004cca58
   ct: fa6f037b47fc21826b610172ca9637e82d6e5801eb31cbd3748271affd4ecb06
   646e0329cbdf3c3cd655b28e82

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: 4e0bc5018beba4bf004cca5b
   ct: 895cabfac50ce6c6eb02ffe6c048bf53b7f7be9a91fc559402cbc5b8dcaeb52b
   2ccc93e466c28fb55fed7a7fec

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: 4e0bc5018beba4bf004cca5d
   ct: 8787491ee8df99bc99a246c4b3216d3d57ab5076e18fa27133f520703bc70ec9
   99dd36ce042e44f0c3169a6a8f

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: 4e0bc5018beba4bf004ccaa6
   ct: 2ad71c85bf3f45c6eca301426289854b31448bcf8a8ccb1deef3ebd87f60848a
   a53c538c30a4dac71d619ee2cd

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: 4e0bc5018beba4bf004ccb59
   ct: 10f179686aa2caec1758c8e554513f16472bd0a11e2a907dde0b212cbe87d74f
   367f8ffe5e41cd3e9962a6afb2

C.3.1.2.  Exported Values








Barnes, et al.             Expires 8 May 2026                  [Page 60]

Internet-Draft                    HPKE                     November 2025


   exporter_context:
   L: 32
   exported_value:
   5e9bc3d236e1911d95e65b576a8a86d478fb827e8bdfe77b741b289890490d4d

   exporter_context: 00
   L: 32
   exported_value:
   6cff87658931bda83dc857e6353efe4987a201b849658d9b047aab4cf216e796

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   d8f1ea7942adbba7412c6d431c62d01371ea476b823eb697e1f6e6cae1dab85a

C.3.2.  PSK Setup Information



































Barnes, et al.             Expires 8 May 2026                  [Page 61]

Internet-Draft                    HPKE                     November 2025


   mode: 1
   kem_id: 16
   kdf_id: 1
   aead_id: 1
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   2afa611d8b1a7b321c761b483b6a053579afa4f767450d3ad0f84a39fda587a6
   pkEm: 04305d35563527bce037773d79a13deabed0e8e7cde61eecee403496959e89
   e4d0ca701726696d1485137ccb5341b3c1c7aaee90a4a02449725e744b1193b53b5f
   skEm:
   57427244f6cc016cddf1c19c8973b4060aa13579b4c067fd5d93a5d74e32a90f
   ikmR:
   d42ef874c1913d9568c9405407c805baddaffd0898a00f1e84e154fa787b2429
   pkRm: 040d97419ae99f13007a93996648b2674e5260a8ebd2b822e84899cd52d874
   46ea394ca76223b76639eccdf00e1967db10ade37db4e7db476261fcc8df97c5ffd1
   skRm:
   438d8bcef33b89e0e9ae5eb0957c353c25a94584b0dd59c991372a75b43cb661
   psk:
   0247fd33b913760fa1fa51e1892d9f307fbe65eb171e8132c2af18555a738b82
   psk_id: 456e6e796e20447572696e206172616e204d6f726961
   enc: 04305d35563527bce037773d79a13deabed0e8e7cde61eecee403496959e89e
   4d0ca701726696d1485137ccb5341b3c1c7aaee90a4a02449725e744b1193b53b5f
   shared_secret:
   2e783ad86a1beae03b5749e0f3f5e9bb19cb7eb382f2fb2dd64c99f15ae0661b
   key_schedule_context: 01b873cdf2dff4c1434988053b7a775e980dd2039ea24f
   950b26b056ccedcb933198e486f9c9c09c9b5c753ac72d6005de254c607d1b534ed1
   1d493ae1c1d9ac85
   secret:
   f2f534e55931c62eeb2188c1f53450354a725183937e68c85e68d6b267504d26
   key: 55d9eb9d26911d4c514a990fa8d57048
   base_nonce: b595dc6b2d7e2ed23af529b1
   exporter_secret:
   895a723a1eab809804973a53c0ee18ece29b25a7555a4808277ad2651d66d705

C.3.2.1.  Encryptions
















Barnes, et al.             Expires 8 May 2026                  [Page 62]

Internet-Draft                    HPKE                     November 2025


   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: b595dc6b2d7e2ed23af529b1
   ct: 90c4deb5b75318530194e4bb62f890b019b1397bbf9d0d6eb918890e1fb2be1a
   c2603193b60a49c2126b75d0eb

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: b595dc6b2d7e2ed23af529b0
   ct: 9e223384a3620f4a75b5a52f546b7262d8826dea18db5a365feb8b997180b22d
   72dc1287f7089a1073a7102c27

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: b595dc6b2d7e2ed23af529b3
   ct: adf9f6000773035023be7d415e13f84c1cb32a24339a32eb81df02be9ddc6abc
   880dd81cceb7c1d0c7781465b2

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: b595dc6b2d7e2ed23af529b5
   ct: 1f4cc9b7013d65511b1f69c050b7bd8bbd5a5c16ece82b238fec4f30ba2400e7
   ca8ee482ac5253cffb5c3dc577

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: b595dc6b2d7e2ed23af5294e
   ct: cdc541253111ed7a424eea5134dc14fc5e8293ab3b537668b8656789628e4589
   4e5bb873c968e3b7cdcbb654a4

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: b595dc6b2d7e2ed23af528b1
   ct: faf985208858b1253b97b60aecd28bc18737b58d1242370e7703ec33b73a4c31
   a1afee300e349adef9015bbbfd

C.3.2.2.  Exported Values








Barnes, et al.             Expires 8 May 2026                  [Page 63]

Internet-Draft                    HPKE                     November 2025


   exporter_context:
   L: 32
   exported_value:
   a115a59bf4dd8dc49332d6a0093af8efca1bcbfd3627d850173f5c4a55d0c185

   exporter_context: 00
   L: 32
   exported_value:
   4517eaede0669b16aac7c92d5762dd459c301fa10e02237cd5aeb9be969430c4

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   164e02144d44b607a7722e58b0f4156e67c0c2874d74cf71da6ca48a4cbdc5e0

C.4.  DHKEM(P-256, HKDF-SHA256), HKDF-SHA512, AES-128-GCM

C.4.1.  Base Setup Information

































Barnes, et al.             Expires 8 May 2026                  [Page 64]

Internet-Draft                    HPKE                     November 2025


   mode: 0
   kem_id: 16
   kdf_id: 3
   aead_id: 1
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   4ab11a9dd78c39668f7038f921ffc0993b368171d3ddde8031501ee1e08c4c9a
   pkEm: 0493ed86735bdfb978cc055c98b45695ad7ce61ce748f4dd63c525a3b8d53a
   15565c6897888070070c1579db1f86aaa56deb8297e64db7e8924e72866f9a472580
   skEm:
   2292bf14bb6e15b8c81a0f45b7a6e93e32d830e48cca702e0affcfb4d07e1b5c
   ikmR:
   ea9ff7cc5b2705b188841c7ace169290ff312a9cb31467784ca92d7a2e6e1be8
   pkRm: 04085aa5b665dc3826f9650ccbcc471be268c8ada866422f739e2d531d4a88
   18a9466bc6b449357096232919ec4fe9070ccbac4aac30f4a1a53efcf7af90610edd
   skRm:
   3ac8530ad1b01885960fab38cf3cdc4f7aef121eaa239f222623614b4079fb38
   enc: 0493ed86735bdfb978cc055c98b45695ad7ce61ce748f4dd63c525a3b8d53a1
   5565c6897888070070c1579db1f86aaa56deb8297e64db7e8924e72866f9a472580
   shared_secret:
   02f584736390fc93f5b4ad039826a3fa08e9911bd1215a3db8e8791ba533cafd
   key_schedule_context: 005b8a3617af7789ee716e7911c7e77f84cdc4cc46e60f
   b7e19e4059f9aeadc00585e26874d1ddde76e551a7679cd47168c466f6e1f705cc93
   74c192778a34fcd5ca221d77e229a9d11b654de7942d685069c633b2362ce3b3d8ea
   4891c9a2a87a4eb7cdb289ba5e2ecbf8cd2c8498bb4a383dc021454d70d46fcbbad1
   252ef4f9
   secret: 0c7acdab61693f936c4c1256c78e7be30eebfe466812f9cc49f0b58dc970
   328dfc03ea359be0250a471b1635a193d2dfa8cb23c90aa2e25025b892a725353eeb
   key: 090ca96e5f8aa02b69fac360da50ddf9
   base_nonce: 9c995e621bf9a20c5ca45546
   exporter_secret: 4a7abb2ac43e6553f129b2c5750a7e82d149a76ed56dc342d7b
   ca61e26d494f4855dff0d0165f27ce57756f7f16baca006539bb8e4518987ba61048
   0ac03efa8

C.4.1.1.  Encryptions
















Barnes, et al.             Expires 8 May 2026                  [Page 65]

Internet-Draft                    HPKE                     November 2025


   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: 9c995e621bf9a20c5ca45546
   ct: d3cf4984931484a080f74c1bb2a6782700dc1fef9abe8442e44a6f09044c8890
   7200b332003543754eb51917ba

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: 9c995e621bf9a20c5ca45547
   ct: d14414555a47269dfead9fbf26abb303365e40709a4ed16eaefe1f2070f1ddeb
   1bdd94d9e41186f124e0acc62d

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: 9c995e621bf9a20c5ca45544
   ct: 9bba136cade5c4069707ba91a61932e2cbedda2d9c7bdc33515aa01dd0e0f7e9
   d3579bf4016dec37da4aafa800

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: 9c995e621bf9a20c5ca45542
   ct: a531c0655342be013bf32112951f8df1da643602f1866749519f5dcb09cc6843
   2579de305a77e6864e862a7600

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: 9c995e621bf9a20c5ca455b9
   ct: be5da649469efbad0fb950366a82a73fefeda5f652ec7d3731fac6c4ffa21a70
   04d2ab8a04e13621bd3629547d

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: 9c995e621bf9a20c5ca45446
   ct: 62092672f5328a0dde095e57435edf7457ace60b26ee44c9291110ec135cb0e1
   4b85594e4fea11247d937deb62

C.4.1.2.  Exported Values








Barnes, et al.             Expires 8 May 2026                  [Page 66]

Internet-Draft                    HPKE                     November 2025


   exporter_context:
   L: 32
   exported_value:
   a32186b8946f61aeead1c093fe614945f85833b165b28c46bf271abf16b57208

   exporter_context: 00
   L: 32
   exported_value:
   84998b304a0ea2f11809398755f0abd5f9d2c141d1822def79dd15c194803c2a

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   93fb9411430b2cfa2cf0bed448c46922a5be9beff20e2e621df7e4655852edbc

C.4.2.  PSK Setup Information



































Barnes, et al.             Expires 8 May 2026                  [Page 67]

Internet-Draft                    HPKE                     November 2025


   mode: 1
   kem_id: 16
   kdf_id: 3
   aead_id: 1
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   c11d883d6587f911d2ddbc2a0859d5b42fb13bf2c8e89ef408a25564893856f5
   pkEm: 04a307934180ad5287f95525fe5bc6244285d7273c15e061f0f2efb211c350
   57f3079f6e0abae200992610b25f48b63aacfcb669106ddee8aa023feed301901371
   skEm:
   a5901ff7d6931959c2755382ea40a4869b1dec3694ed3b009dda2d77dd488f18
   ikmR:
   75bfc2a3a3541170a54c0b06444e358d0ee2b4fb78a401fd399a47a33723b700
   pkRm: 043f5266fba0742db649e1043102b8a5afd114465156719cea90373229aabd
   d84d7f45dabfc1f55664b888a7e86d594853a6cccdc9b189b57839cbbe3b90b55873
   skRm:
   bc6f0b5e22429e5ff47d5969003f3cae0f4fec50e23602e880038364f33b8522
   psk:
   0247fd33b913760fa1fa51e1892d9f307fbe65eb171e8132c2af18555a738b82
   psk_id: 456e6e796e20447572696e206172616e204d6f726961
   enc: 04a307934180ad5287f95525fe5bc6244285d7273c15e061f0f2efb211c3505
   7f3079f6e0abae200992610b25f48b63aacfcb669106ddee8aa023feed301901371
   shared_secret:
   2912aacc6eaebd71ff715ea50f6ef3a6637856b2a4c58ea61e0c3fc159e3bc16
   key_schedule_context: 01713f73042575cebfd132f0cc4338523f8eae95c80a74
   9f7cf3eb9436ff1c612ca62c37df27ca46d2cc162445a92c5f5fdc57bcde129ca7b1
   f284b0c12297c037ca221d77e229a9d11b654de7942d685069c633b2362ce3b3d8ea
   4891c9a2a87a4eb7cdb289ba5e2ecbf8cd2c8498bb4a383dc021454d70d46fcbbad1
   252ef4f9
   secret: ff2051d2128d5f3078de867143e076262ce1d0aecafc3fff3d607f1eaff0
   5345c7d5ffcb3202cdecb3d1a2f7da20592a237747b6e855390cbe2109d3e6ac70c2
   key: 0b910ba8d9cfa17e5f50c211cb32839a
   base_nonce: 0c29e714eb52de5b7415a1b7
   exporter_secret: 50c0a182b6f94b4c0bd955c4aa20df01f282cc12c43065a0812
   fe4d4352790171ed2b2c4756ad7f5a730ba336c8f1edd0089d8331192058c385bae3
   9c7cc8b57

C.4.2.1.  Encryptions













Barnes, et al.             Expires 8 May 2026                  [Page 68]

Internet-Draft                    HPKE                     November 2025


   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: 0c29e714eb52de5b7415a1b7
   ct: 57624b6e320d4aba0afd11f548780772932f502e2ba2a8068676b2a0d3b5129a
   45b9faa88de39e8306da41d4cc

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: 0c29e714eb52de5b7415a1b6
   ct: 159d6b4c24bacaf2f5049b7863536d8f3ffede76302dace42080820fa51925d4
   e1c72a64f87b14291a3057e00a

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: 0c29e714eb52de5b7415a1b5
   ct: bd24140859c99bf0055075e9c460032581dd1726d52cf980d308e9b20083ca62
   e700b17892bcf7fa82bac751d0

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: 0c29e714eb52de5b7415a1b3
   ct: 93ddd55f82e9aaaa3cfc06840575f09d80160b20538125c2549932977d1238dd
   e8126a4a91118faf8632f62cb8

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: 0c29e714eb52de5b7415a148
   ct: 377a98a3c34bf716581b05a6b3fdc257f245856384d5f2241c8840571c52f5c8
   5c21138a4a81655edab8fe227d

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: 0c29e714eb52de5b7415a0b7
   ct: cc161f5a179831d456d119d2f2c19a6817289c75d1c61cd37ac8a450acd9efba
   02e0ac00d128c17855931ff69a

C.4.2.2.  Exported Values








Barnes, et al.             Expires 8 May 2026                  [Page 69]

Internet-Draft                    HPKE                     November 2025


   exporter_context:
   L: 32
   exported_value:
   8158bea21a6700d37022bb7802866edca30ebf2078273757b656ef7fc2e428cf

   exporter_context: 00
   L: 32
   exported_value:
   6a348ba6e0e72bb3ef22479214a139ef8dac57be34509a61087a12565473da8d

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   2f6d4f7a18ec48de1ef4469f596aada4afdf6d79b037ed3c07e0118f8723bffc

C.5.  DHKEM(P-256, HKDF-SHA256), HKDF-SHA256, ChaCha20Poly1305

C.5.1.  Base Setup Information

































Barnes, et al.             Expires 8 May 2026                  [Page 70]

Internet-Draft                    HPKE                     November 2025


   mode: 0
   kem_id: 16
   kdf_id: 1
   aead_id: 3
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   f1f1a3bc95416871539ecb51c3a8f0cf608afb40fbbe305c0a72819d35c33f1f
   pkEm: 04c07836a0206e04e31d8ae99bfd549380b072a1b1b82e563c935c09582782
   4fc1559eac6fb9e3c70cd3193968994e7fe9781aa103f5b50e934b5b2f387e381291
   skEm:
   7550253e1147aae48839c1f8af80d2770fb7a4c763afe7d0afa7e0f42a5b3689
   ikmR:
   61092f3f56994dd424405899154a9918353e3e008171517ad576b900ddb275e7
   pkRm: 04a697bffde9405c992883c5c439d6cc358170b51af72812333b015621dc0f
   40bad9bb726f68a5c013806a790ec716ab8669f84f6b694596c2987cf35baba2a006
   skRm:
   a4d1c55836aa30f9b3fbb6ac98d338c877c2867dd3a77396d13f68d3ab150d3b
   enc: 04c07836a0206e04e31d8ae99bfd549380b072a1b1b82e563c935c095827824
   fc1559eac6fb9e3c70cd3193968994e7fe9781aa103f5b50e934b5b2f387e381291
   shared_secret:
   806520f82ef0b03c823b7fc524b6b55a088f566b9751b89551c170f4113bd850
   key_schedule_context: 00b738cd703db7b4106e93b4621e9a19c89c838e559642
   40e5d3f331aaf8b0d58b2e986ea1c671b61cf45eec134dac0bae58ec6f63e790b140
   0b47c33038b0269c
   secret:
   fe891101629aa355aad68eff3cc5170d057eca0c7573f6575e91f9783e1d4506
   key:
   a8f45490a92a3b04d1dbf6cf2c3939ad8bfc9bfcb97c04bffe116730c9dfe3fc
   base_nonce: 726b4390ed2209809f58c693
   exporter_secret:
   4f9bd9b3a8db7d7c3a5b9d44fdc1f6e37d5d77689ade5ec44a7242016e6aa205

C.5.1.1.  Encryptions


















Barnes, et al.             Expires 8 May 2026                  [Page 71]

Internet-Draft                    HPKE                     November 2025


   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: 726b4390ed2209809f58c693
   ct: 6469c41c5c81d3aa85432531ecf6460ec945bde1eb428cb2fedf7a29f5a685b4
   ccb0d057f03ea2952a27bb458b

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: 726b4390ed2209809f58c692
   ct: f1564199f7e0e110ec9c1bcdde332177fc35c1adf6e57f8d1df24022227ffa87
   16862dbda2b1dc546c9d114374

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: 726b4390ed2209809f58c691
   ct: 39de89728bcb774269f882af8dc5369e4f3d6322d986e872b3a8d074c7c18e85
   49ff3f85b6d6592ff87c3f310c

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: 726b4390ed2209809f58c697
   ct: bc104a14fbede0cc79eeb826ea0476ce87b9c928c36e5e34dc9b6905d91473ec
   369a08b1a25d305dd45c6c5f80

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: 726b4390ed2209809f58c66c
   ct: 8f2814a2c548b3be50259713c6724009e092d37789f6856553d61df23ebc0792
   35f710e6af3c3ca6eaba7c7c6c

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: 726b4390ed2209809f58c793
   ct: b45b69d419a9be7219d8c94365b89ad6951caf4576ea4774ea40e9b7047a09d6
   537d1aa2f7c12d6ae4b729b4d0

C.5.1.2.  Exported Values








Barnes, et al.             Expires 8 May 2026                  [Page 72]

Internet-Draft                    HPKE                     November 2025


   exporter_context:
   L: 32
   exported_value:
   9b13c510416ac977b553bf1741018809c246a695f45eff6d3b0356dbefe1e660

   exporter_context: 00
   L: 32
   exported_value:
   6c8b7be3a20a5684edecb4253619d9051ce8583baf850e0cb53c402bdcaf8ebb

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   477a50d804c7c51941f69b8e32fe8288386ee1a84905fe4938d58972f24ac938

C.5.2.  PSK Setup Information



































Barnes, et al.             Expires 8 May 2026                  [Page 73]

Internet-Draft                    HPKE                     November 2025


   mode: 1
   kem_id: 16
   kdf_id: 1
   aead_id: 3
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   e1a4e1d50c4bfcf890f2b4c7d6b2d2aca61368eddc3c84162df2856843e1057a
   pkEm: 04f336578b72ad7932fe867cc4d2d44a718a318037a0ec271163699cee653f
   a805c1fec955e562663e0c2061bb96a87d78892bff0cc0bad7906c2d998ebe1a7246
   skEm:
   7d6e4e006cee68af9b3fdd583a0ee8962df9d59fab029997ee3f456cbc857904
   ikmR:
   ee51dec304abf993ef8fd52aacdd3b539108bbf6e491943266c1de89ec596a17
   pkRm: 041eb8f4f20ab72661af369ff3231a733672fa26f385ffb959fd1bae46bfda
   43ad55e2d573b880831381d9367417f554ce5b2134fbba5235b44db465feffc6189e
   skRm:
   12ecde2c8bc2d5d7ed2219c71f27e3943d92b344174436af833337c557c300b3
   psk:
   0247fd33b913760fa1fa51e1892d9f307fbe65eb171e8132c2af18555a738b82
   psk_id: 456e6e796e20447572696e206172616e204d6f726961
   enc: 04f336578b72ad7932fe867cc4d2d44a718a318037a0ec271163699cee653fa
   805c1fec955e562663e0c2061bb96a87d78892bff0cc0bad7906c2d998ebe1a7246
   shared_secret:
   ac4f260dce4db6bf45435d9c92c0e11cfdd93743bd3075949975974cc2b3d79e
   key_schedule_context: 01622b72afcc3795841596c67ea74400ca3b029374d7d5
   640bda367c5d67b3fbeb2e986ea1c671b61cf45eec134dac0bae58ec6f63e790b140
   0b47c33038b0269c
   secret:
   858c8087a1c056db5811e85802f375bb0c19b9983204a1575de4803575d23239
   key:
   6d61cb330b7771168c8619498e753f16198aad9566d1f1c6c70e2bc1a1a8b142
   base_nonce: 0de7655fb65e1cd51a38864e
   exporter_secret:
   754ca00235b245e72d1f722a7718e7145bd113050a2aa3d89586d4cb7514bfdb

C.5.2.1.  Encryptions















Barnes, et al.             Expires 8 May 2026                  [Page 74]

Internet-Draft                    HPKE                     November 2025


   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: 0de7655fb65e1cd51a38864e
   ct: 21433eaff24d7706f3ed5b9b2e709b07230e2b11df1f2b1fe07b3c70d5948a53
   d6fa5c8bed194020bd9df0877b

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: 0de7655fb65e1cd51a38864f
   ct: c74a764b4892072ea8c2c56b9bcd46c7f1e9ca8cb0a263f8b40c2ba59ac9c857
   033f176019562218769d3e0452

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: 0de7655fb65e1cd51a38864c
   ct: dc8cd68863474d6e9cbb6a659335a86a54e036249d41acf909e738c847ff2bd3
   6fe3fcacda4ededa7032c0a220

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: 0de7655fb65e1cd51a38864a
   ct: cd54a8576353b1b9df366cb0cc042e46eef6f4cf01e205fe7d47e306b2fdd90f
   7185f289a26c613ca094e3be10

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: 0de7655fb65e1cd51a3886b1
   ct: 6324570c9d542c70c7e70570c1d8f4c52a89484746bf0625441890ededcc80c2
   4ef2301c38bfd34d689d19f67d

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: 0de7655fb65e1cd51a38874e
   ct: 1ea6326c8098ed0437a553c466550114fb2ca1412cca7de98709b9ccdf19206e
   52c3d39180e2cf62b3e9f4baf4

C.5.2.2.  Exported Values








Barnes, et al.             Expires 8 May 2026                  [Page 75]

Internet-Draft                    HPKE                     November 2025


   exporter_context:
   L: 32
   exported_value:
   530bbc2f68f078dccc89cc371b4f4ade372c9472bafe4601a8432cbb934f528d

   exporter_context: 00
   L: 32
   exported_value:
   6e25075ddcc528c90ef9218f800ca3dfe1b8ff4042de5033133adb8bd54c401d

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   6f6fbd0d1c7733f796461b3235a856cc34f676fe61ed509dfc18fa16efe6be78

C.6.  DHKEM(P-521, HKDF-SHA512), HKDF-SHA512, AES-256-GCM

C.6.1.  Base Setup Information

































Barnes, et al.             Expires 8 May 2026                  [Page 76]

Internet-Draft                    HPKE                     November 2025


   mode: 0
   kem_id: 18
   kdf_id: 3
   aead_id: 2
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE: 7f06ab8215105fc46aceeb2e3dc5028b44364f960426eb0d8e4026c2f8b5d7
   e7a986688f1591abf5ab753c357a5d6f0440414b4ed4ede71317772ac98d9239f709
   04
   pkEm: 040138b385ca16bb0d5fa0c0665fbbd7e69e3ee29f63991d3e9b5fa740aab8
   900aaeed46ed73a49055758425a0ce36507c54b29cc5b85a5cee6bae0cf1c21f2731
   ece2013dc3fb7c8d21654bb161b463962ca19e8c654ff24c94dd2898de12051f1ed0
   692237fb02b2f8d1dc1c73e9b366b529eb436e98a996ee522aef863dd5739d2f29b0
   skEm: 014784c692da35df6ecde98ee43ac425dbdd0969c0c72b42f2e708ab9d5354
   15a8569bdacfcc0a114c85b8e3f26acf4d68115f8c91a66178cdbd03b7bcc5291e37
   4b
   ikmR: 2ad954bbe39b7122529f7dde780bff626cd97f850d0784a432784e69d86ecc
   aade43b6c10a8ffdb94bf943c6da479db137914ec835a7e715e36e45e29b587bab3b
   f1
   pkRm: 0401b45498c1714e2dce167d3caf162e45e0642afc7ed435df7902ccae0e84
   ba0f7d373f646b7738bbbdca11ed91bdeae3cdcba3301f2457be452f271fa6837580
   e661012af49583a62e48d44bed350c7118c0d8dc861c238c72a2bda17f64704f464b
   57338e7f40b60959480c0e58e6559b190d81663ed816e523b6b6a418f66d2451ec64
   skRm: 01462680369ae375e4b3791070a7458ed527842f6a98a79ff5e0d4cbde83c2
   7196a3916956655523a6a2556a7af62c5cadabe2ef9da3760bb21e005202f7b24628
   47
   enc: 040138b385ca16bb0d5fa0c0665fbbd7e69e3ee29f63991d3e9b5fa740aab89
   00aaeed46ed73a49055758425a0ce36507c54b29cc5b85a5cee6bae0cf1c21f2731e
   ce2013dc3fb7c8d21654bb161b463962ca19e8c654ff24c94dd2898de12051f1ed06
   92237fb02b2f8d1dc1c73e9b366b529eb436e98a996ee522aef863dd5739d2f29b0
   shared_secret: 776ab421302f6eff7d7cb5cb1adaea0cd50872c71c2d63c30c4f1
   d5e43653336fef33b103c67e7a98add2d3b66e2fda95b5b2a667aa9dac7e59cc1d46
   d30e818
   key_schedule_context: 0083a27c5b2358ab4dae1b2f5d8f57f10ccccc822a4733
   26f543f239a70aee46347324e84e02d7651a10d08fb3dda739d22d50c53fbfa8122b
   aacd0f9ae5913072ef45baa1f3a4b169e141feb957e48d03f28c837d8904c3d67753
   08c3d3faa75dd64adfa44e1a1141edf9349959b8f8e5291cbdc56f62b0ed6527d692
   e85b09a4
   secret: 49fd9f53b0f93732555b2054edfdc0e3101000d75df714b98ce5aa295a37
   f1b18dfa86a1c37286d805d3ea09a20b72f93c21e83955a1f01eb7c5eead563d21e7
   key:
   751e346ce8f0ddb2305c8a2a85c70d5cf559c53093656be636b9406d4d7d1b70
   base_nonce: 55ff7a7d739c69f44b25447b
   exporter_secret: e4ff9dfbc732a2b9c75823763c5ccc954a2c0648fc6de80a585
   81252d0ee3215388a4455e69086b50b87eb28c169a52f42e71de4ca61c920e7bd24c
   95cc3f992

C.6.1.1.  Encryptions




Barnes, et al.             Expires 8 May 2026                  [Page 77]

Internet-Draft                    HPKE                     November 2025


   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: 55ff7a7d739c69f44b25447b
   ct: 170f8beddfe949b75ef9c387e201baf4132fa7374593dfafa90768788b7b2b20
   0aafcc6d80ea4c795a7c5b841a

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: 55ff7a7d739c69f44b25447a
   ct: d9ee248e220ca24ac00bbbe7e221a832e4f7fa64c4fbab3945b6f3af0c5ecd5e
   16815b328be4954a05fd352256

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: 55ff7a7d739c69f44b254479
   ct: 142cf1e02d1f58d9285f2af7dcfa44f7c3f2d15c73d460c48c6e0e506a3144ba
   e35284e7e221105b61d24e1c7a

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: 55ff7a7d739c69f44b25447f
   ct: 3bb3a5a07100e5a12805327bf3b152df728b1c1be75a9fd2cb2bf5eac0cca1fb
   80addb37eb2a32938c7268e3e5

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: 55ff7a7d739c69f44b254484
   ct: 4f268d0930f8d50b8fd9d0f26657ba25b5cb08b308c92e33382f369c768b558e
   113ac95a4c70dd60909ad1adc7

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: 55ff7a7d739c69f44b25457b
   ct: dbbfc44ae037864e75f136e8b4b4123351d480e6619ae0e0ae437f036f2f8f1e
   f677686323977a1ccbb4b4f16a

C.6.1.2.  Exported Values








Barnes, et al.             Expires 8 May 2026                  [Page 78]

Internet-Draft                    HPKE                     November 2025


   exporter_context:
   L: 32
   exported_value:
   05e2e5bd9f0c30832b80a279ff211cc65eceb0d97001524085d609ead60d0412

   exporter_context: 00
   L: 32
   exported_value:
   fca69744bb537f5b7a1596dbf34eaa8d84bf2e3ee7f1a155d41bd3624aa92b63

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   f389beaac6fcf6c0d9376e20f97e364f0609a88f1bc76d7328e9104df8477013

C.6.2.  PSK Setup Information

   mode: 1
   kem_id: 18
   kdf_id: 3
   aead_id: 2
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE: f3ebfa9a69a924e672114fcd9e06fa9559e937f7eccce4181a2b506df53dbe
   514be12f094bb28e01de19dd345b4f7ede5ad7eaa6b9c3019592ec68eaae9a14732c
   e0
   pkEm: 040085eff0835cc84351f32471d32aa453cdc1f6418eaaecf1c2824210eb1d
   48d0768b368110fab21407c324b8bb4bec63f042cfa4d0868d19b760eb4beba1bff7
   93b30036d2c614d55730bd2a40c718f9466faf4d5f8170d22b6df98dfe0c067d02b3
   49ae4a142e0c03418f0a1479ff78a3db07ae2c2e89e5840f712c174ba2118e90fdcb
   skEm: 012e5cfe0daf5fe2a1cd617f4c4bae7c86f1f527b3207f115e262a98cc6526
   8ec88cb8645aec73b7aa0a472d0292502d1078e762646e0c093cf873243d12c39915
   f6
   ikmR: a2a2458705e278e574f835effecd18232f8a4c459e7550a09d44348ae5d3b1
   ea9d95c51995e657ad6f7cae659f5e186126a471c017f8f5e41da9eba74d4e0473e1
   79
   pkRm: 04006917e049a2be7e1482759fb067ddb94e9c4f7f5976f655088dec452466
   14ff924ed3b385fc2986c0ecc39d14f907bf837d7306aada59dd5889086125ecd038
   ead400603394b5d81f89ebfd556a898cc1d6a027e143d199d3db845cb91c5289fb26
   c5ff80832935b0e8dd08d37c6185a6f77683347e472d1edb6daa6bd7652fea628fae
   skRm: 011bafd9c7a52e3e71afbdab0d2f31b03d998a0dc875dd7555c63560e142bd
   e264428de03379863b4ec6138f813fa009927dc5d15f62314c56d4e7ff2b485753eb
   72
   psk:
   0247fd33b913760fa1fa51e1892d9f307fbe65eb171e8132c2af18555a738b82
   psk_id: 456e6e796e20447572696e206172616e204d6f726961
   enc: 040085eff0835cc84351f32471d32aa453cdc1f6418eaaecf1c2824210eb1d4
   8d0768b368110fab21407c324b8bb4bec63f042cfa4d0868d19b760eb4beba1bff79
   3b30036d2c614d55730bd2a40c718f9466faf4d5f8170d22b6df98dfe0c067d02b34



Barnes, et al.             Expires 8 May 2026                  [Page 79]

Internet-Draft                    HPKE                     November 2025


   9ae4a142e0c03418f0a1479ff78a3db07ae2c2e89e5840f712c174ba2118e90fdcb
   shared_secret: 0d52de997fdaa4797720e8b1bebd3df3d03c4cf38cc8c1398168d
   36c3fc7626428c9c254dd3f9274450909c64a5b3acbe45e2d850a2fd69ac0605fe5c
   8a057a5
   key_schedule_context: 0124497637cf18d6fbcc16e9f652f00244c981726f293b
   b7819861e85e50c94f0be30e022ab081e18e6f299fd3d3d976a4bc590f85bc7711bf
   ce32ee1a7fb1c154ef45baa1f3a4b169e141feb957e48d03f28c837d8904c3d67753
   08c3d3faa75dd64adfa44e1a1141edf9349959b8f8e5291cbdc56f62b0ed6527d692
   e85b09a4
   secret: 2cf425e26f65526afc0634a3dba4e28d980c1015130ce07c2ac7530d7a39
   1a75e5a0db428b09f27ad4d975b4ad1e7f85800e03ffeea35e8cf3fe67b18d4a1345
   key:
   f764a5a4b17e5d1ffba6e699d65560497ebaea6eb0b0d9010a6d979e298a39ff
   base_nonce: 479afdf3546ddba3a9841f38
   exporter_secret: 5c3d4b65a13570502b93095ef196c42c8211a4a188c4590d358
   63665c705bb140ecba6ce9256be3fad35b4378d41643867454612adfd0542a684b61
   799bf293f

C.6.2.1.  Encryptions
































Barnes, et al.             Expires 8 May 2026                  [Page 80]

Internet-Draft                    HPKE                     November 2025


   sequence number: 0
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d30
   nonce: 479afdf3546ddba3a9841f38
   ct: de69e9d943a5d0b70be3359a19f317bd9aca4a2ebb4332a39bcdfc97d5fe62f3
   a77702f4822c3be531aa7843a1

   sequence number: 1
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d31
   nonce: 479afdf3546ddba3a9841f39
   ct: 77a16162831f90de350fea9152cfc685ecfa10acb4f7994f41aed43fa5431f23
   82d078ec88baec53943984553e

   sequence number: 2
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d32
   nonce: 479afdf3546ddba3a9841f3a
   ct: f1d48d09f126b9003b4c7d3fe6779c7c92173188a2bb7465ba43d899a6398a33
   3914d2bb19fd769d53f3ec7336

   sequence number: 4
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d34
   nonce: 479afdf3546ddba3a9841f3c
   ct: 829b11c082b0178082cd595be6d73742a4721b9ac05f8d2ef8a7704a53022d82
   bd0d8571f578c5c13b99eccff8

   sequence number: 255
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323535
   nonce: 479afdf3546ddba3a9841fc7
   ct: a3ee291e20f37021e82df14d41f3fbe98b27c43b318a36cacd8471a3b1051ab1
   2ee055b62ded95b72a63199a3f

   sequence number: 256
   pt: 4265617574792069732074727574682c20747275746820626561757479
   aad: 436f756e742d323536
   nonce: 479afdf3546ddba3a9841e38
   ct: eecc2173ce1ac14b27ee67041e90ed50b7809926e55861a579949c07f6d26137
   bf9cf0d097f60b5fd2fbf348ec

C.6.2.2.  Exported Values








Barnes, et al.             Expires 8 May 2026                  [Page 81]

Internet-Draft                    HPKE                     November 2025


   exporter_context:
   L: 32
   exported_value:
   62691f0f971e34de38370bff24deb5a7d40ab628093d304be60946afcdb3a936

   exporter_context: 00
   L: 32
   exported_value:
   76083c6d1b6809da088584674327b39488eaf665f0731151128452e04ce81bff

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   0c7cfc0976e25ae7680cf909ae2de1859cd9b679610a14bec40d69b91785b2f6

C.7.  DHKEM(X25519, HKDF-SHA256), HKDF-SHA256, Export-Only AEAD

C.7.1.  Base Setup Information

































Barnes, et al.             Expires 8 May 2026                  [Page 82]

Internet-Draft                    HPKE                     November 2025


   mode: 0
   kem_id: 32
   kdf_id: 1
   aead_id: 65535
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   55bc245ee4efda25d38f2d54d5bb6665291b99f8108a8c4b686c2b14893ea5d9
   pkEm:
   e5e8f9bfff6c2f29791fc351d2c25ce1299aa5eaca78a757c0b4fb4bcd830918
   skEm:
   095182b502f1f91f63ba584c7c3ec473d617b8b4c2cec3fad5af7fa6748165ed
   ikmR:
   683ae0da1d22181e74ed2e503ebf82840deb1d5e872cade20f4b458d99783e31
   pkRm:
   194141ca6c3c3beb4792cd97ba0ea1faff09d98435012345766ee33aae2d7664
   skRm:
   33d196c830a12f9ac65d6e565a590d80f04ee9b19c83c87f2c170d972a812848
   enc:
   e5e8f9bfff6c2f29791fc351d2c25ce1299aa5eaca78a757c0b4fb4bcd830918
   shared_secret:
   e81716ce8f73141d4f25ee9098efc968c91e5b8ce52ffff59d64039e82918b66
   key_schedule_context: 009bd09219212a8cf27c6bb5d54998c5240793a70ca0a8
   92234bd5e082bc619b6a3f4c22aa6d9a0424c2b4292fdf43b8257df93c2f6adbf6dd
   c9c64fee26bdd292
   secret:
   04d64e0620aa047e9ab833b0ebcd4ff026cefbe44338fd7d1a93548102ee01af
   key:
   base_nonce:
   exporter_secret:
   79dc8e0509cf4a3364ca027e5a0138235281611ca910e435e8ed58167c72f79b

C.7.1.1.  Exported Values

   exporter_context:
   L: 32
   exported_value:
   7a36221bd56d50fb51ee65edfd98d06a23c4dc87085aa5866cb7087244bd2a36

   exporter_context: 00
   L: 32
   exported_value:
   d5535b87099c6c3ce80dc112a2671c6ec8e811a2f284f948cec6dd1708ee33f0

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   ffaabc85a776136ca0c378e5d084c9140ab552b78f039d2e8775f26efff4c70e




Barnes, et al.             Expires 8 May 2026                  [Page 83]

Internet-Draft                    HPKE                     November 2025


C.7.2.  PSK Setup Information

   mode: 1
   kem_id: 32
   kdf_id: 1
   aead_id: 65535
   info: 4f6465206f6e2061204772656369616e2055726e
   ikmE:
   c51211a8799f6b8a0021fcba673d9c4067a98ebc6794232e5b06cb9febcbbdf5
   pkEm:
   d3805a97cbcd5f08babd21221d3e6b362a700572d14f9bbeb94ec078d051ae3d
   skEm:
   1d72396121a6a826549776ef1a9d2f3a2907fc6a38902fa4e401afdb0392e627
   ikmR:
   5e0516b1b29c0e13386529da16525210c796f7d647c37eac118023a6aa9eb89a
   pkRm:
   d53af36ea5f58f8868bb4a1333ed4cc47e7a63b0040eb54c77b9c8ec456da824
   skRm:
   98f304d4ecb312689690b113973c61ffe0aa7c13f2fbe365e48f3ed09e5a6a0c
   psk:
   0247fd33b913760fa1fa51e1892d9f307fbe65eb171e8132c2af18555a738b82
   psk_id: 456e6e796e20447572696e206172616e204d6f726961
   enc:
   d3805a97cbcd5f08babd21221d3e6b362a700572d14f9bbeb94ec078d051ae3d
   shared_secret:
   024573db58c887decb4c57b6ed39f2c9a09c85600a8a0ecb11cac24c6aaec195
   key_schedule_context: 01446fb1fe2632a0a338f0a85ed1f3a0ac475bdea2cd72
   f8c713b3a46ee737379a3f4c22aa6d9a0424c2b4292fdf43b8257df93c2f6adbf6dd
   c9c64fee26bdd292
   secret:
   638b94532e0d0bf812cf294f36b97a5bdcb0299df36e22b7bb6858e3c113080b
   key:
   base_nonce:
   exporter_secret:
   04261818aeae99d6aba5101bd35ddf3271d909a756adcef0d41389d9ed9ab153

C.7.2.1.  Exported Values














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   exporter_context:
   L: 32
   exported_value:
   be6c76955334376aa23e936be013ba8bbae90ae74ed995c1c6157e6f08dd5316

   exporter_context: 00
   L: 32
   exported_value:
   1721ed2aa852f84d44ad020c2e2be4e2e6375098bf48775a533505fd56a3f416

   exporter_context: 54657374436f6e74657874
   L: 32
   exported_value:
   7c9d79876a288507b81a5a52365a7d39cc0fa3f07e34172984f96fec07c44cba

Authors' Addresses

   Richard L. Barnes
   Cisco
   Email: rlb@ipv.sx


   Karthik Bhargavan
   Inria
   Email: karthikeyan.bhargavan@inria.fr


   Benjamin Lipp
   Inria
   Email: ietf@benjaminlipp.de


   Christopher A. Wood
   Email: caw@heapingbits.net

















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name: draft-ietf-lamps-rfc7030-csrattrs
rev: 23
title: Clarification and enhancement of RFC7030 CSR Attributes definition
time: 2026-01-06T19:11:51Z
group_uri: /api/v1/group/group/2164/
expires: 2025-12-31T00:06:48Z
ad: /api/v1/person/person/123703/
shepherd: /api/v1/person/email/housley@vigilsec.com/
categories: ["Data formats/interop", "Policy/governance"]
tags: []
fetched_at: 2026-02-27T22:56:09.014925+00:00
abstract:
This document updates RFC7030, Enrollment over Secure Transport
   (EST), clarifying how the Certificate Signiing Request (CSR)
   Attributes Response can be used by an EST server to specify both CSR
   attribute Object IDs (OID) and also CSR attribute values, in
   particular X.509 extension values, that the server expects the client
   to include in subsequent CSR request.  RFC9148 is derived from
   RFC7030, and it is also updated.

   RFC7030 (EST) is ambiguous in its specification of the CSR Attributes
   Response.  This has resulted in implementation challenges and
   implementor confusion.  As a result, there was not universal
   understanding of what was specified.  This document clarifies the
   encoding rules.

   This document therefore also provides a new straightforward approach:
   using a template for CSR contents that may be partially filled in by
   the server.  This also allows an EST server to specify a subject
   Distinguished Name (DN).

states:
["/api/v1/doc/state/3/", "/api/v1/doc/state/108/", "/api/v1/doc/state/154/", "/api/v1/doc/state/115/", "/api/v1/doc/state/7/", "/api/v1/doc/state/44/"]

full_text:
LAMPS Working Group                                   M. Richardson, Ed.
Internet-Draft                                  Sandelman Software Works
Updates: 70309148 (if approved)                                 O. Friel
Intended status: Standards Track                                   Cisco
Expires: 30 December 2025                                  D. von Oheimb
                                                                 Siemens
                                                              D. Harkins
                                                   The Industrial Lounge
                                                            28 June 2025


   Clarification and enhancement of RFC7030 CSR Attributes definition
                  draft-ietf-lamps-rfc7030-csrattrs-23

Abstract

   This document updates RFC7030, Enrollment over Secure Transport
   (EST), clarifying how the Certificate Signiing Request (CSR)
   Attributes Response can be used by an EST server to specify both CSR
   attribute Object IDs (OID) and also CSR attribute values, in
   particular X.509 extension values, that the server expects the client
   to include in subsequent CSR request.  RFC9148 is derived from
   RFC7030, and it is also updated.

   RFC7030 (EST) is ambiguous in its specification of the CSR Attributes
   Response.  This has resulted in implementation challenges and
   implementor confusion.  As a result, there was not universal
   understanding of what was specified.  This document clarifies the
   encoding rules.

   This document therefore also provides a new straightforward approach:
   using a template for CSR contents that may be partially filled in by
   the server.  This also allows an EST server to specify a subject
   Distinguished Name (DN).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.







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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 30 December 2025.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  CSR Attributes Handling . . . . . . . . . . . . . . . . . . .   4
     3.1.  Extensions to RFC 7030 section 2.6  . . . . . . . . . . .   4
     3.2.  Extensions to RFC 7030 section 4.5.2  . . . . . . . . . .   4
     3.3.  Update to RFC9148 . . . . . . . . . . . . . . . . . . . .   6
     3.4.  Use of CSR templates  . . . . . . . . . . . . . . . . . .   6
   4.  Co-existence with existing implementations  . . . . . . . . .  11
   5.  Examples using the original RFC 7030 approach . . . . . . . .  11
     5.1.  Require an RFC8994/ACP subjectAltName with specific
           otherName . . . . . . . . . . . . . . . . . . . . . . . .  11
       5.1.1.  Base64 encoded example  . . . . . . . . . . . . . . .  11
       5.1.2.  ASN.1 DUMP output . . . . . . . . . . . . . . . . . .  11
     5.2.  RFC7030 original example  . . . . . . . . . . . . . . . .  13
       5.2.1.  Base64 encoded example  . . . . . . . . . . . . . . .  13
       5.2.2.  ASN.1 DUMP output . . . . . . . . . . . . . . . . . .  13
     5.3.  Require a specific subjectAltName extension . . . . . . .  14
       5.3.1.  Base64 encoded example  . . . . . . . . . . . . . . .  14
       5.3.2.  ASN.1 DUMP output . . . . . . . . . . . . . . . . . .  14
     5.4.  Require a public key of a specific size . . . . . . . . .  15
       5.4.1.  Base64 encoded example  . . . . . . . . . . . . . . .  15
       5.4.2.  ASN.1 DUMP output . . . . . . . . . . . . . . . . . .  16
     5.5.  Require a public key of a specific curve  . . . . . . . .  16
       5.5.1.  Base64 encoded example  . . . . . . . . . . . . . . .  16
       5.5.2.  ASN.1 DUMP output . . . . . . . . . . . . . . . . . .  16



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     5.6.  Require specific extensions and attributes  . . . . . . .  17
       5.6.1.  Base64 encoded example  . . . . . . . . . . . . . . .  17
       5.6.2.  ASN.1 DUMP output . . . . . . . . . . . . . . . . . .  17
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
     6.1.  Identity and Privacy Considerations . . . . . . . . . . .  18
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  19
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  20
   Appendix A.  ASN.1 Module . . . . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

1.  Introduction

   This document updates RFC7030 Enrollment over Secure Transport (EST)
   and clarifies how the Certificate Signing Request (CSR) Attributes
   Response can be used by an EST server to specify both CSR attribute
   OIDs and also CSR attribute values.  In particular, the server needs
   to be able to specify X.509 extension values that it expects the
   client to include in the subsequent CSR.

   Enrollment over Secure Transport [RFC7030] (EST) has been used in a
   wide variety of applications.  In particular, [RFC8994] and [RFC8995]
   describe a way to use it in order to build out an Autonomic Control
   Plane (ACP) [RFC8368].

   When bootstrapping the ACP, there is a requirement that each node be
   given a very specific subjectAltName.  In [RFC8994], the ACP
   specification, the EST server is specified to make use of the CSR
   Attributes ("/csrattrs") resource (specified in [RFC7030],
   Section 2.6) to convey to the EST client the actual subjectAltName
   that needs to go into its CSR and thus ultimately into its End Entity
   certificate.

   As a result of some implementation challenges, it came to light that
   this particular way of using the CSR attributes was not universally
   agreed upon, and it was suggested that it went contrary to [RFC7030],
   Section 2.6.

   [RFC7030], Section 2.6 says that the CSR attributes "can provide
   additional descriptive information that the EST server cannot access
   itself".  This is extended to describe how the EST server can provide
   values that it demands be used.

   After significant discussion, it has been determined that Section 4.5
   of [RFC7030] specification is sufficiently difficult to read and
   ambiguous to interpret that clarification is needed.



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   Also, [RFC7030], Section 4.5.2 is extended to clarify the use of the
   existing ASN.1 syntax [X.680][X.690].

   This covers all uses and is fully backward compatible with existing
   use, including addressesing the needs of [RFC8994] and [RFC8995].

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  CSR Attributes Handling

3.1.  Extensions to RFC 7030 section 2.6

   Replace the second paragraph with the following text:

   These attributes can provide additional information that
   the EST server cannot access itself, such as the Media Access Control
   (MAC) address of an interface of the EST client. The EST server can
   also provide concrete values that it tells the client to include in
   the CSR, such as a specific X.509 Subject Alternative Name extension.
   Moreover, these attributes can indicate the type of the included
   public key or which crypto algorithms to use for the self-signature,
   such as a specific elliptic curve or a specific hash function that
   the client is expected to use when generating the CSR.

3.2.  Extensions to RFC 7030 section 4.5.2

   The ASN.1 syntax for CSR Attributes as defined in EST [RFC7030],
   Section 4.5.2 is as follows:

      CsrAttrs ::= SEQUENCE SIZE (0..MAX) OF AttrOrOID

      AttrOrOID ::= CHOICE (oid OBJECT IDENTIFIER, attribute Attribute }

      Attribute { ATTRIBUTE:IOSet } ::= SEQUENCE {
           type   ATTRIBUTE.&id({IOSet}),
           values SET SIZE(1..MAX) OF ATTRIBUTE.&Type({IOSet}{@type}) }

   This remains unchanged, such that bits-on-the-wire compatibility is
   maintained.






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   Key parts that were unclear were which OID to use in the 'type' field
   and that the 'values' field can contain an entire sequence of X.509
   extensions.

   The OID to use for such attributes in the 'type' field MUST be id-
   ExtensionReq, which has the value 1.2.840.113549.1.9.14.  Note that
   is the same as pkcs-9-at-extensionRequest defined in PKCS#9
   [RFC2985].  There MUST be only one such attribute.

   The 'values' field of this attribute MUST contain a set with exactly
   one element, and this element MUST be of type Extensions, as per
   Section 4.1 of [RFC5280]:

      Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension

      Extension  ::=  SEQUENCE  {
           extnID      OBJECT IDENTIFIER,
           critical    BOOLEAN DEFAULT FALSE,
           extnValue   OCTET STRING
                       -- contains the DER encoding of an ASN.1 value
                       -- corresponding to the extension type identified
                       -- by extnID
           }

   An Extension comprises the OID of the specific X.509 extension
   (extnID), optionally the 'critical' bit, and the extension value
   (extnValue).

   An Extensions structure, which is a sequence of elements of type
   Extension, MUST NOT include more than one element with a particular
   extnID.

   When not using the template-based approach of Section 3.4, specifying
   the requirement for a public key of a specific type and optionally
   its size and other parameters MUST be done as follows: Include
   exactly one Attribute with the type field being the OID specifying
   the type of the key, such as ecPublicKey or rsaEncryption.  The
   'values' field MAY be empty to indicate no further requirements on
   the key.  Otherwise, it MUST contain suitable parameters for the
   given key type, such as a singleton set containing the OID of an EC
   curve such as secp384r1 or containing an integer value for the RSA
   key size such as 4096.  Many examples for this are given in
   Section 5.








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3.3.  Update to RFC9148

   The updates to EST in this THISRFC equally apply when using CoAP as a
   transport as described in [RFC9148].  THISRFC therefore adds the
   following paragraph after the second paragraph of [RFC9148],
   Section 1:

      |  RFC EDITOR: Please replace THISRFC with the RFC number for this
      |  document.

   EST over CoAP as specified in {{RFC9148}} applies unchanged to
   {{RFC7030}} updated by THISRFC.  Hence, all references to {{RFC7030}}
   in {{RFC9148}} are assumed to indicate {{RFC7030}} updated by
   THISRFC.

3.4.  Use of CSR templates

   Alternatively to the unstructured inclusion of CSR attributes
   specified in [RFC7030], Section 4.5.2 with its limitations and
   ambiguities, Appendix B of [RFC8295] describes an approach using a
   CSR template.  An entire CSR object is returned with various fields
   filled out, and other fields waiting to be filled in.  In that
   approach, a pKCS7PDU attribute includes a Full PKI Data content type
   [RFC5272] and that in turn includes an [RFC2986] CSR or a Certificate
   Request Message Format (CRMF) formatted request (for details see
   [RFC6268] Sections 5 or 9, respectively).

   One drawback to that approach, particularly for the CSR, is that some
   unused fields have to be included; specifically, the 'signature'
   field on the CSR is faked with an empty bit string.

   A similar method has been defined in CMP Updates [RFC9480] and the
   Lightweight CMP profile [RFC9483], Section 4.3.3, using a CSR
   template as defined for CRMF [RFC4211].  Like the approach mentioned
   before, this method does not properly deal with absent Relative
   Distinguished Name (RDN) values, as it would encode them as invalid
   empty strings.  Also encoding an absent 'subjectPublicKey' value as
   an empty BIT STRING and an absent X.509 extension value as an empty
   OCTET STRING can cause issues with strict ASN.1 parsing and decoding.

   These drawbacks are avoided as follows:

   This specification defines a new Certificate Request Information
   Template attribute for CsrAttrs (as given in Section 3.2) that is
   essentially a partially filled in PKCS#10 CSR minus the signature
   wrapper:





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     CertificationRequestInfoTemplate ::= SEQUENCE {
         version       INTEGER { v1(0) } (v1, ... ),
         subject       NameTemplate OPTIONAL,
         subjectPKInfo [0] SubjectPublicKeyInfoTemplate
                                   {{ PKInfoAlgorithms }} OPTIONAL,
         attributes    [1] Attributes{{ CRIAttributes }}
     }

   Appendix A contains all detail.

   The CertificationRequestInfoTemplate closely resembles the
   CertificationRequestInfo from [RFC5912], Section 5:

     CertificationRequestInfo ::= SEQUENCE {
       version       INTEGER { v1(0) } (v1,...),
       subject       Name,
       subjectPKInfo SubjectPublicKeyInfo{{ PKInfoAlgorithms }},
       attributes    [0] Attributes{{ CRIAttributes }}
     }

   with the following differences.

   *  The 'subject' field has been made OPTIONAL.  It MUST be present if
      the server places any requirements on the RDNs of the subject
      name; otherwise, it MUST be absent.

   *  RelativeDistinguishedNames (RDNs) in the 'subject' fields are
      allowed to have no value, which has been achieved by adding
      OPTIONAL to the 'value' field of SingleAttributeTemplate.  If the
      client is expected to provide an RDN of a certain type such as
      commonName, the respective RDN MUST be present in the 'subject'
      field; otherwise it MUST be absent.  If the server in addition
      gives an RDN value, this means that the client is expected to use
      this value for the RDN, otherwise the client is expected to fill
      in a suitable value.  The example at the end of this section has a
      'subject' field that contains both forms of RDN specifications.

     SingleAttributeTemplate {ATTRIBUTE:AttrSet} ::= SEQUENCE {
         type      ATTRIBUTE.&id({AttrSet}),
         value     ATTRIBUTE.&Type({AttrSet}{@type}) OPTIONAL
     }

   *  The 'subjectPKInfo' field has been made OPTIONAL.  The field MUST
      be absent if the server places no requirements on the key.
      Otherwise, it MUST be present, and the 'algorithm' field specifies
      the type of the key pair the client is expected to use.





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   *  The 'subjectPublicKey' field contained in
      SubjectPublicKeyInfoTemplate has been made OPTIONAL because
      usually it is not needed.  In case the server requires use of an
      RSA key and needs to specify its size, the field MUST be present
      and contain a placeholder public key value of the desired RSA
      modulus length.  Otherwise, the subjectPublicKey MUST be absent.

     SubjectPublicKeyInfoTemplate{PUBLIC-KEY:IOSet} ::= SEQUENCE {
         algorithm        AlgorithmIdentifier{PUBLIC-KEY, {IOSet}},
         subjectPublicKey BIT STRING OPTIONAL
     }

   *  A new OID id-aa-extensionReqTemplate and the related
      ExtensionTemplate structure is defined where the 'extnValue' field
      has been made OPTIONAL.  This is only needed to enable specifying
      partial extensions with values to be filled in by the client;
      otherwise the id-ExtensionReq OID and the respective value of type
      ExtensionReq MUST be used for specifying requirements on X.509
      extensions.

   For each extension of type Extension or ExtensionTemplate provided by
   the server, the client is expected to include an extension of the
   type given by the extnID.  If the 'critical' field is present, the
   client SHOULD use it in the extension as well.  If the 'extnValue' is
   present (which is always the case when type Extension is used), the
   client SHOULD use the given extension value in its CSR.  When the
   type ExtensionTemplate is used, the 'extnValue' can be absent, and
   then the client SHOULD provide an extension value in an Extension
   with the given extnID.  For instance, if the server includes an
   ExtensionTemplate with the extnID 'subjectAltName' but without an
   extnValue, the client SHOULD include a SAN extension with a suitable
   value.

   In case the server includes an ExtensionTemplate with the extnID
   'subjectAltName' and a partially filled in extnValue, such as a
   'directoryName' choice containing the NULL-DN (i.e., an empty
   sequence of RDNs) or the 'iPAddress' choice with an empty OCTET
   STRING, this means that the client SHOULD fill in the respective
   GeneralName value.












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   ExtensionTemplate {EXTENSION:ExtensionSet} ::= SEQUENCE {
      extnID      EXTENSION.&id({ExtensionSet}),
      critical    BOOLEAN DEFAULT FALSE,
      extnValue   OCTET STRING (CONTAINING
                  EXTENSION.&ExtnType({ExtensionSet}{@extnID})) OPTIONAL
                  --  contains the DER encoding of the ASN.1 value
                  --  corresponding to the extension type identified
                  --  by extnID when present
   }

   The 'version' field of the CertificationRequestInfoTemplate MUST
   contain v1 (0).

   The 'attributes' field MUST NOT contain multiple id-aa-
   extensionReqTemplate attributes and MUST NOT contain both id-
   ExtensionReq and id-aa-extensionReqTemplate attributes.

   The 'values' field of an id-aa-extensionReqTemplate attribute MUST
   contain a set with exactly one element, and this element MUST be of
   type ExtensionTemplate.

   Suppose the server requires that the CSR will contain:

   *  the 'subject' field with a common name to be filled in by the EE
      and two organizational unit names with given values "myDept" and
      "myGroup",

   *  the 'publicKey' field contains an Elliptic Curve Cryptography
      (ECC) key on curve secp256r1,

   *  the 'subjectAltName' extension with two entries; one DNS entry
      with name "www.myServer.com" and IP entry that is empty for the IP
      address to be filled in.

   *  the 'keyUsage' extension marked critical with the value
      digitalSignature and keyAgreement, and

   *  the 'extKeyUsage' extension with value to be filled in by the EE.

   Then the CertificationRequestInfo structure constructed by the server
   will be as follows:

   SEQUENCE {
     INTEGER 0
     SEQUENCE {
       SET {
         SEQUENCE {
           OBJECT IDENTIFIER commonName (2 5 4 3)



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           }
         }
       SET {
         SEQUENCE {
           OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
           UTF8String "myDept"
           }
         }
       SET {
         SEQUENCE {
           OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
           UTF8String "myGroup"
           }
         }
       }
     [0] {
       SEQUENCE {
         OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
         OBJECT IDENTIFIER secp256r1 (1 2 840 10045 3 1 7)
         }
       }
     [1] {
       SEQUENCE {
         OBJECT IDENTIFIER id-aa-extensionReqTemplate
                           (1 2 840 113549 1 9 TBD3)
         SET {
           SEQUENCE {
             SEQUENCE {
               OBJECT IDENTIFIER subjectAltName (2 5 29 17)
               OCTET STRING, encapsulates {
                 SEQUENCE {
                   [2] "www.myServer.com"
                   [7] ""
                   }
                 }
               }
             SEQUENCE {
               OBJECT IDENTIFIER keyUsage (2 5 29 15)
               BOOLEAN TRUE
               OCTET STRING, encapsulates {
                 BIT STRING 3 unused bits
                   "10001"B
                 }
               }
             SEQUENCE {
               OBJECT IDENTIFIER extKeyUsage (2 5 29 37)
               }
             }



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           }
         }
       }
     }

4.  Co-existence with existing implementations

   EST servers with legacy clients MAY continue to use the [RFC7030]-
   style unstructured list of attribute/value pairs, and MAY also
   include the template style described in Section 3.4 for newer
   clients.  Clients which understand both MUST use the template only,
   and ignore all other CSRattrs elements.  Older clients will ignore
   the new CertificationRequestInfoTemplate element.

5.  Examples using the original RFC 7030 approach

   Each example has a high-level (English) explanation of what is
   expected.  Some mapping back to the Attribute and Extension
   definitions above are included.  The base64 DER encoding is then
   shown.  The output of "dumpasn1" [dumpasn1] is then provided to
   detail what the contents are.

5.1.  Require an RFC8994/ACP subjectAltName with specific otherName

   A single subjectAltName extension is specified in a single [RFC7030]
   CsrAttrs attribute with OID 'id-ExtensionReq' indicating type
   Extensions.  This is what might be created by an [RFC8995] Registrar
   that is asking for [RFC8994] AcpNodeName with format 'otherNames'.

5.1.1.  Base64 encoded example

   The Base64:

   MGgwZgYJKoZIhvcNAQkOMVkwVzBVBgNVHREBAf8ESzBJoEcG
   CCsGAQUFBwgKoDsWOXJmYzg5OTQrZmQ3MzlmYzIzYzM0NDAx
   MTIyMzM0NDU1MDAwMDAwMDArQGFjcC5leGFtcGxlLmNvbQ==

5.1.2.  ASN.1 DUMP output

   There is a single subjectAltName Extension with an Attribute with
   Extension type.










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       <30 68>
     0 104: SEQUENCE {
       <30 66>
     2 102:   SEQUENCE {
       <06 09>
     4   9:     OBJECT IDENTIFIER
          :       extensionRequest (1 2 840 113549 1 9 14)
          :       (PKCS #9 via CRMF)
       <31 59>
    15  89:     SET {
       <30 57>
    17  87:       SEQUENCE {
       <30 55>
    19  85:         SEQUENCE {
       <06 03>
    21   3:           OBJECT IDENTIFIER
          :             subjectAltName (2 5 29 17)
          :             (X.509 extension)
       <01 01>
    26   1:           BOOLEAN TRUE
       <04 4B>
    29  75:           OCTET STRING, encapsulates {
       <30 49>
    31  73:             SEQUENCE {
       <A0 47>
    33  71:               [0] {
       <06 08>
    35   8:                 OBJECT IDENTIFIER '1 3 6 1 5 5 7 8 10'
       <A0 3B>
    45  59:                 [0] {
       <16 39>
    47  57:                   IA5String
          :                   'rfc8994+fd739fc23c34401122334455'
          :                   '00000000+@acp.example.com'
          :                   }
          :                 }
          :               }
          :             }
          :           }
          :         }
          :       }
          :     }
          :   }








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5.2.  RFC7030 original example

   In this example, taken from [RFC7030], Section 4.5.2, a few different
   attributes are included.  The original encoding of the 'macAddress'
   part in the example is NOT CORRECT.  It was not aligned with the
   definition of the Extension Request attribute as specified in
   Section 5.4.2 of [RFC2985].  The revised encoding given here does not
   use an 'id-ExtensionReq' attribute because the MAC Address is not an
   X.509 certificate extension by itself and because the server provides
   its OID without a value, which is not allowed syntactically within a
   structure of type 'Extension'.

5.2.1.  Base64 encoded example

   The Base64:

   MDIGCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAiBgcr
   BgEBAQEWBggqhkjOPQQDAw==

5.2.2.  ASN.1 DUMP output

   The CsrAttrs structure contains:

   1.  The challengePassword attribute is included to indicate that the
       CSR should include this value.

   2.  An ecPublicKey OID is provided with the value secp384r1 to
       indicate what kind of public key should be submitted.

   3.  The macAddress OID 1.3.6.1.1.1.1.22 is included to indicate that
       the CSR is expected to include (in a subjectDirectoryAttributes
       extension) a MAC address value.

   4.  The ecdsaWithSHA384 OID is included to indicate what kind of hash
       is expected to be used for the self-signature in the PKCS#10 CSR.
















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       <30 32>
     0  50: SEQUENCE {
       <06 09>
     2   9:   OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7)
          :     (PKCS #9)
       <30 12>
    13  18:   SEQUENCE {
       <06 07>
    15   7:     OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
          :       (ANSI X9.62 public key type)
       <31 07>
    24   7:     SET {
       <06 05>
    26   5:       OBJECT IDENTIFIER secp384r1 (1 3 132 0 34)
          :         (SECG (Certicom) named elliptic curve)
          :       }
          :     }
       <06 07>
    33   7:   OBJECT IDENTIFIER '1 3 6 1 1 1 1 22'
       <06 08>
    42   8:   OBJECT IDENTIFIER ecdsaWithSHA384 (1 2 840 10045 4 3 3)
          :     (ANSI X9.62 ECDSA algorithm with SHA384)
          :   }

5.3.  Require a specific subjectAltName extension

   This example is the same as the previous one except that instead of
   the OID for a macAddress, a subjectAltName is specified as the only
   Extension element.

5.3.1.  Base64 encoded example

   The Base64:

   MEUGCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAjBgkq
   hkiG9w0BCRQGCgmSJomT8ixkAQUGA1UEBQYIKoZIzj0EAwQ=

5.3.2.  ASN.1 DUMP output

   The CsrAttrs structure contains:

   1.  The challengePassword attribute is included to indicate that the
       CSR should include this value.

   2.  An ecPublicKey OID is provided with the value secp521r1 to
       indicate what kind of public key should be submitted.





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   3.  An extensionRequest container with a subjectAltName value
       containing the name potato@example.com

   4.  The ecdsaWithSHA512 OID is included to indicate the SHA-512 hash
       is expected to be used for the self-signature in the PKCS#10 CSR.

    <30 45>
  0  69: SEQUENCE {
    <06 09>
  2   9:   OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7)
       :     (PKCS #9)
    <30 12>
 13  18:   SEQUENCE {
    <06 07>
 15   7:     OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
       :       (ANSI X9.62 public key type)
    <31 07>
 24   7:     SET {
    <06 05>
 26   5:       OBJECT IDENTIFIER secp521r1 (1 3 132 0 35)
       :         (SECG (Certicom) named elliptic curve)
       :       }
       :     }
    <06 09>
 33   9:   OBJECT IDENTIFIER friendlyName (for PKCS #12) (1 2 840 113549 1 9 20)
       :     (PKCS #9 via PKCS #12)
    <06 0A>
 44  10:   OBJECT IDENTIFIER '0 9 2342 19200300 100 1 5'
    <06 03>
 56   3:   OBJECT IDENTIFIER serialNumber (2 5 4 5)
       :     (X.520 DN component)
    <06 08>
 61   8:   OBJECT IDENTIFIER ecdsaWithSHA512 (1 2 840 10045 4 3 4)
       :     (ANSI X9.62 ECDSA algorithm with SHA512)
       :   }

5.4.  Require a public key of a specific size

   (RFC-editor please remove: Example ref Harkins01)

   The CSR requires an RSA public key of a specific size.

5.4.1.  Base64 encoded example

   The Base64:

   MCkGCSqGSIb3DQEJBzARBgkqhkiG9w0BAQExBAICEAAGCSqG
   SIb3DQEBCw==



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5.4.2.  ASN.1 DUMP output

   Provide a CSR with an RSA key that's 4096 bits and use SHA256 as the
   hash algorithm within the signature.

       <30 29>
     0  41: SEQUENCE {
       <06 09>
     2   9:   OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7)
          :     (PKCS #9)
       <30 11>
    13  17:   SEQUENCE {
       <06 09>
    15   9:     OBJECT IDENTIFIER rsaEncryption (1 2 840 113549 1 1 1)
          :       (PKCS #1)
       <31 04>
    26   4:     SET {
       <02 02>
    28   2:       INTEGER 4096
          :       }
          :     }
       <06 09>
    32   9:   OBJECT IDENTIFIER sha256WithRSAEncryption
                                (1 2 840 113549 1 1 11)
          :     (PKCS #1)
          :   }

5.5.  Require a public key of a specific curve

   (RFC-editor please remove: Example ref Harkins02)

   The CSR requires an ECC public key with a specific curve.

5.5.1.  Base64 encoded example

   The Base64:

   MC4GCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAiBgNV
   BAUGCCqGSM49BAMD

5.5.2.  ASN.1 DUMP output

   Provide a CSR with an ECC key from p384, include your serial number,
   and use SHA384 as the hash algorithm within the signature.







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       <30 2E>
     0  46: SEQUENCE {
       <06 09>
     2   9:   OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7)
          :     (PKCS #9)
       <30 12>
    13  18:   SEQUENCE {
       <06 07>
    15   7:     OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
          :       (ANSI X9.62 public key type)
       <31 07>
    24   7:     SET {
       <06 05>
    26   5:       OBJECT IDENTIFIER secp384r1 (1 3 132 0 34)
          :         (SECG (Certicom) named elliptic curve)
          :       }
          :     }
       <06 03>
    33   3:   OBJECT IDENTIFIER serialNumber (2 5 4 5)
          :     (X.520 DN component)
       <06 08>
    38   8:   OBJECT IDENTIFIER ecdsaWithSHA384 (1 2 840 10045 4 3 3)
          :     (ANSI X9.62 ECDSA algorithm with SHA384)
          :   }

5.6.  Require specific extensions and attributes

   (RFC-editor please remove: Example ref Harkins03)

   The CSR is required to have an EC key, to include a serial number, a
   friendly name, favorite drink [favoritedrink] [OID
   0.9.2342.19200300.100.1.5], and use SHA512 as the hash algorithm
   within the signature.

5.6.1.  Base64 encoded example

   The Base64:

   MEUGCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAjBgkq
   hkiG9w0BCRQGCgmSJomT8ixkAQUGA1UEBQYIKoZIzj0EAwQ=

5.6.2.  ASN.1 DUMP output

   Provide a CSR with an EC key from sha521, include your serial number,
   friendly name, and favorite drink, and hash it with SHA512.






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    <30 45>
  0  69: SEQUENCE {
    <06 09>
  2   9:   OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7)
       :     (PKCS #9)
    <30 12>
 13  18:   SEQUENCE {
    <06 07>
 15   7:     OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
       :       (ANSI X9.62 public key type)
    <31 07>
 24   7:     SET {
    <06 05>
 26   5:       OBJECT IDENTIFIER secp521r1 (1 3 132 0 35)
       :         (SECG (Certicom) named elliptic curve)
       :       }
       :     }
    <06 09>
 33   9:   OBJECT IDENTIFIER friendlyName (for PKCS #12) (1 2 840 113549 1 9 20)
       :     (PKCS #9 via PKCS #12)
    <06 0A>
 44  10:   OBJECT IDENTIFIER '0 9 2342 19200300 100 1 5'
    <06 03>
 56   3:   OBJECT IDENTIFIER serialNumber (2 5 4 5)
       :     (X.520 DN component)
    <06 08>
 61   8:   OBJECT IDENTIFIER ecdsaWithSHA512 (1 2 840 10045 4 3 4)
       :     (ANSI X9.62 ECDSA algorithm with SHA512)
       :   }

6.  Security Considerations

   The security considerations from EST [RFC7030] section 6 are
   unchanged.

6.1.  Identity and Privacy Considerations

   An EST server may use this mechanism to instruct the EST client about
   the identities it should include in the CSR it sends as part of
   enrollment.  The client may only be aware of its IDevID Subject,
   which includes a manufacturer serial number.  The EST server can use
   this mechanism to tell the client to include a specific fully
   qualified domain name in the CSR in order to complete domain
   ownership proofs required by the CA.  Additionally, the EST server
   may deem the manufacturer serial number in an IDevID as personally
   identifiable information, and may want to specify a new random opaque
   identifier that the pledge should use in its CSR.  This may be
   desirable if the CA and EST server have different operators.



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7.  IANA Considerations

   IANA is asked to allocate three new Object Identifiers:

   *  One (TBD1) from the SMI Security for S/MIME Module Identifier
      (1.2.840.113549.1.9.16.0) registry for the ASN.1 module: id-mod-
      critemplate; see Appendix A

   *  One (TBD2) from the SMI Security for S/MIME Attributes
      (1.2.840.113549.1.9.16.2) registry for the Certification Request
      Information Template (id-aa-certificationRequestInfoTemplate)
      attribute; see Appendix A

   *  One (TBD3) SMI Security for S/MIME Attributes
      (1.2.840.113549.1.9.16.2) registry for the extension request
      template (id-aa-extensionReqTemplate) attribute; see Appendix A

8.  Acknowledgments

   Corey Bonnell crafted example02 using a different tool, and this
   helped debug other running code.

   Carl Wallace provided major parts of the
   CertificationRequestInfoTemplate syntax declaration.

   Russ Housley did many reviews of the ASN.1 and suggested many fixes.

   Deb Cooley did the usual Area Director Review.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              DOI 10.17487/RFC2986, November 2000,
              <https://www.rfc-editor.org/rfc/rfc2986>.

   [RFC5911]  Hoffman, P. and J. Schaad, "New ASN.1 Modules for
              Cryptographic Message Syntax (CMS) and S/MIME", RFC 5911,
              DOI 10.17487/RFC5911, June 2010,
              <https://www.rfc-editor.org/rfc/rfc5911>.




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   [RFC5912]  Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
              Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
              DOI 10.17487/RFC5912, June 2010,
              <https://www.rfc-editor.org/rfc/rfc5912>.

   [RFC6268]  Schaad, J. and S. Turner, "Additional New ASN.1 Modules
              for the Cryptographic Message Syntax (CMS) and the Public
              Key Infrastructure Using X.509 (PKIX)", RFC 6268,
              DOI 10.17487/RFC6268, July 2011,
              <https://www.rfc-editor.org/rfc/rfc6268>.

   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
              "Enrollment over Secure Transport", RFC 7030,
              DOI 10.17487/RFC7030, October 2013,
              <https://www.rfc-editor.org/rfc/rfc7030>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC9148]  van der Stok, P., Kampanakis, P., Richardson, M., and S.
              Raza, "EST-coaps: Enrollment over Secure Transport with
              the Secure Constrained Application Protocol", RFC 9148,
              DOI 10.17487/RFC9148, April 2022,
              <https://www.rfc-editor.org/rfc/rfc9148>.

   [X.680]    ITU-T, "Information technology -- Abstract Syntax Notation
              One (ASN.1): Specification of basic notation", ITU-T
              Recommendation X.680, ISO/IEC 8824-1:2021, February 2021,
              <https://www.itu.int/rec/T-REC-X.680>.

   [X.690]    ITU-T, "Information technology -- ASN.1 encoding rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER)", ITU-T Recommendation X.690, ISO/IEC 8825-1:2021,
              February 2021, <https://www.itu.int/rec/T-REC-X.690>.

9.2.  Informative References

   [dumpasn1] Gutmann, P., "Dump ASN", n.d.,
              <https://www.cs.auckland.ac.nz/~pgut001/dumpasn1.c>.

   [favoritedrink]
              "Favorite Drink: arbitrary OID", n.d.,
              <https://oid-base.com/get/0.9.2342.19200300.100.1.5>.






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   [RFC2985]  Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
              Classes and Attribute Types Version 2.0", RFC 2985,
              DOI 10.17487/RFC2985, November 2000,
              <https://www.rfc-editor.org/rfc/rfc2985>.

   [RFC4211]  Schaad, J., "Internet X.509 Public Key Infrastructure
              Certificate Request Message Format (CRMF)", RFC 4211,
              DOI 10.17487/RFC4211, September 2005,
              <https://www.rfc-editor.org/rfc/rfc4211>.

   [RFC5272]  Schaad, J. and M. Myers, "Certificate Management over CMS
              (CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
              <https://www.rfc-editor.org/rfc/rfc5272>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/rfc/rfc5280>.

   [RFC8295]  Turner, S., "EST (Enrollment over Secure Transport)
              Extensions", RFC 8295, DOI 10.17487/RFC8295, January 2018,
              <https://www.rfc-editor.org/rfc/rfc8295>.

   [RFC8368]  Eckert, T., Ed. and M. Behringer, "Using an Autonomic
              Control Plane for Stable Connectivity of Network
              Operations, Administration, and Maintenance (OAM)",
              RFC 8368, DOI 10.17487/RFC8368, May 2018,
              <https://www.rfc-editor.org/rfc/rfc8368>.

   [RFC8994]  Eckert, T., Ed., Behringer, M., Ed., and S. Bjarnason, "An
              Autonomic Control Plane (ACP)", RFC 8994,
              DOI 10.17487/RFC8994, May 2021,
              <https://www.rfc-editor.org/rfc/rfc8994>.

   [RFC8995]  Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
              May 2021, <https://www.rfc-editor.org/rfc/rfc8995>.

   [RFC9480]  Brockhaus, H., von Oheimb, D., and J. Gray, "Certificate
              Management Protocol (CMP) Updates", RFC 9480,
              DOI 10.17487/RFC9480, November 2023,
              <https://www.rfc-editor.org/rfc/rfc9480>.







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   [RFC9483]  Brockhaus, H., von Oheimb, D., and S. Fries, "Lightweight
              Certificate Management Protocol (CMP) Profile", RFC 9483,
              DOI 10.17487/RFC9483, November 2023,
              <https://www.rfc-editor.org/rfc/rfc9483>.

Appendix A.  ASN.1 Module

      |  RFC EDITOR: Please replace TBD1, TBD2, and TBD3 with the value
      |  assigned by IANA during the publication of this document.

   This appendix provides an ASN.1 module [X.680] for the Certification
   Request Information Template attribute, and it follows the
   conventions established in [RFC5911], [RFC5912], and [RFC6268].

   CRITemplateModule
     { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
       pkcs-9(9) smime(16) modules(0) id-mod-critemplate(TBD1) }

   DEFINITIONS IMPLICIT TAGS ::=

   BEGIN

   IMPORTS -- from [RFC5912]

   SupportedAttributes
    FROM PKIX1Explicit-2009
     { iso(1) identified-organization(3) dod(6) internet(1) security(5)
       mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51)}

   ATTRIBUTE, EXTENSION
    FROM PKIX-CommonTypes-2009
     { iso(1) identified-organization(3) dod(6) internet(1) security(5)
       mechanisms(5) pkix(7) id-mod(0) id-mod-pkixCommon-02(57) }

   PUBLIC-KEY, AlgorithmIdentifier{}
    FROM AlgorithmInformation-2009
     { iso(1) identified-organization(3) dod(6) internet(1) security(5)
       mechanisms(5) pkix(7) id-mod(0)
       id-mod-algorithmInformation-02(58)}

   CertExtensions
    FROM PKIX1Implicit-2009
     { iso(1) identified-organization(3) dod(6) internet(1) security(5)
       mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-implicit-02(59)}

   Attributes{}, CRIAttributes, PKInfoAlgorithms
    FROM PKCS-10
     { iso(1) identified-organization(3) dod(6) internet(1)



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       security(5) mechanisms(5) pkix(7)
       id-mod(0) id-mod-pkcs10-2009(69) }
   ;

   aa-certificationRequestInfoTemplate ATTRIBUTE ::=
     { TYPE CertificationRequestInfoTemplate IDENTIFIED BY
       id-aa-certificationRequestInfoTemplate }

   id-aa-certificationRequestInfoTemplate OBJECT IDENTIFIER ::=
     { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
       smime(16) aa(2) id-aa-certificationRequestInfoTemplate(TBD2) }

   --  like CertificationRequestInfo but OPTIONAL subject, subjectPKInfo
   CertificationRequestInfoTemplate ::= SEQUENCE {
       version       INTEGER { v1(0) } (v1, ... ),
       subject       NameTemplate OPTIONAL,
       subjectPKInfo [0] SubjectPublicKeyInfoTemplate
                                 {{ PKInfoAlgorithms }} OPTIONAL,
       attributes    [1] Attributes{{ CRIAttributes }}
   }


   --  like Name, but with OPTIONAL RDN values
   NameTemplate ::= CHOICE { -- only one possibility for now --
       rdnSequence  RDNSequenceTemplate }

   RDNSequenceTemplate ::= SEQUENCE OF RelativeDistinguishedNameTemplate

   RelativeDistinguishedNameTemplate  ::= SET SIZE (1 .. MAX)
       OF SingleAttributeTemplate { {SupportedAttributes} }

   --  like Attributes, but with OPTIONAL value
   SingleAttributeTemplates{ATTRIBUTE:AttrSet} ::= SEQUENCE OF
       SingleAttributeTemplates{ {AttrSet} }

   --  like SingleAttribute, but with OPTIONAL value
   SingleAttributeTemplate{ATTRIBUTE:AttrSet} ::= SEQUENCE {
       type      ATTRIBUTE.&id({AttrSet}),
       value     ATTRIBUTE.&Type({AttrSet}{@type}) OPTIONAL
   }

   --  like SubjectPublicKeyInfo, but with OPTIONAL subjectPublicKey
   SubjectPublicKeyInfoTemplate{PUBLIC-KEY:IOSet} ::= SEQUENCE {
       algorithm        AlgorithmIdentifier{PUBLIC-KEY, {IOSet}},
       subjectPublicKey BIT STRING OPTIONAL
   }

   id-aa-extensionReqTemplate OBJECT IDENTIFIER ::=



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   { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
     smime(16) aa(2) id-aa-extensionReqTemplate(TBD3) }

   --  like extensionRequest, but with OPTIONAL Extension extnValues
   --  original definition was in PKCS#9 RFC 2985 section 5.4.2
   at-extensionReqTemplate ATTRIBUTE ::= {
       TYPE ExtensionReqTemplate IDENTIFIED BY id-aa-extensionReqTemplate }

   ExtensionReqTemplate ::= ExtensionTemplates{{CertExtensions}}

   --  like Extensions, but with OPTIONAL extnValue
   ExtensionTemplates{EXTENSION:ExtensionSet} ::=
       SEQUENCE SIZE (1..MAX) OF ExtensionTemplate{{ExtensionSet}}

   --  like Extension, but with OPTIONAL extnValue
   ExtensionTemplate{EXTENSION:ExtensionSet} ::= SEQUENCE {
       extnID    EXTENSION.&id({ExtensionSet}),
       critical  BOOLEAN
     --                   (EXTENSION.&Critical({ExtensionSet}{@extnID}))
                        DEFAULT FALSE,
       extnValue OCTET STRING (CONTAINING
                 EXTENSION.&ExtnType({ExtensionSet}{@extnID})) OPTIONAL
                 --  contains the DER encoding of the ASN.1 value
                 --  corresponding to the extension type identified
                 --  by extnID when present
   }

   END

Authors' Addresses

   Michael Richardson (editor)
   Sandelman Software Works
   Email: mcr+ietf@sandelman.ca


   Owen Friel
   Cisco
   Email: ofriel@cisco.com


   Dr. David von Oheimb
   Siemens
   Email: dev@ddvo.net


   Dan Harkins
   The Industrial Lounge



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   Email: dharkins@lounge.org


















































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name: draft-ietf-suit-firmware-encryption
rev: 26
title: Encrypted Payloads in SUIT Manifests
time: 2025-12-08T19:57:52Z
group_uri: /api/v1/group/group/2211/
expires: 2026-06-11T19:12:27Z
ad: /api/v1/person/person/123703/
shepherd: /api/v1/person/email/akira.tsukamoto@gmail.com/
categories: ["Data formats/interop"]
tags: []
fetched_at: 2026-02-27T22:56:09.014930+00:00
abstract:
This document specifies techniques for encrypting software, firmware,
   machine learning models, and personalization data by utilizing the
   IETF SUIT manifest.  Key agreement is provided by ephemeral-static
   (ES) Diffie-Hellman (DH) and AES Key Wrap (AES-KW).  ES-DH uses
   public key cryptography while AES-KW uses a pre-shared key.
   Encryption of the plaintext is accomplished with conventional
   symmetric key cryptography.

states:
["/api/v1/doc/state/1/", "/api/v1/doc/state/108/", "/api/v1/doc/state/115/", "/api/v1/doc/state/17/", "/api/v1/doc/state/34/", "/api/v1/doc/state/44/"]

full_text:
SUIT                                                       H. Tschofenig
Internet-Draft                                                     H-BRS
Intended status: Standards Track                              R. Housley
Expires: 11 June 2026                                     Vigil Security
                                                                B. Moran
                                                             Arm Limited
                                                                D. Brown
                                                                  Linaro
                                                             K. Takayama
                                                         SECOM CO., LTD.
                                                         8 December 2025


                  Encrypted Payloads in SUIT Manifests
                 draft-ietf-suit-firmware-encryption-26

Abstract

   This document specifies techniques for encrypting software, firmware,
   machine learning models, and personalization data by utilizing the
   IETF SUIT manifest.  Key agreement is provided by ephemeral-static
   (ES) Diffie-Hellman (DH) and AES Key Wrap (AES-KW).  ES-DH uses
   public key cryptography while AES-KW uses a pre-shared key.
   Encryption of the plaintext is accomplished with conventional
   symmetric key cryptography.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 11 June 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Terminology . . . . . . . . . . . . . . . . .   4
   3.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Encryption Extensions . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Directive Write . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Directive Copy  . . . . . . . . . . . . . . . . . . . . .   9
     4.3.  Authenticating the Payload  . . . . . . . . . . . . . . .   9
   5.  Content Key Distribution  . . . . . . . . . . . . . . . . . .  10
     5.1.  Content Key Distribution with AES Key Wrap  . . . . . . .  11
       5.1.1.  Introduction  . . . . . . . . . . . . . . . . . . . .  11
       5.1.2.  Deployment Options  . . . . . . . . . . . . . . . . .  11
       5.1.3.  The CDDL of SUIT_Encryption_Info for AES-KW binary  .  12
     5.2.  Content Key Distribution with Ephemeral-Static
           Diffie-Hellman  . . . . . . . . . . . . . . . . . . . . .  13
       5.2.1.  Introduction  . . . . . . . . . . . . . . . . . . . .  13
       5.2.2.  Deployment Options  . . . . . . . . . . . . . . . . .  14
       5.2.3.  The CDDL of SUIT_Encryption_Info for ES-DH binary . .  15
       5.2.4.  Context Information Structure . . . . . . . . . . . .  16
   6.  Content Encryption  . . . . . . . . . . . . . . . . . . . . .  17
     6.1.  AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . .  18
       6.1.1.  Introduction  . . . . . . . . . . . . . . . . . . . .  18
       6.1.2.  AES-KW + AES-GCM Example  . . . . . . . . . . . . . .  19
       6.1.3.  ECDH-ES+AES-KW + AES-GCM Example  . . . . . . . . . .  20
     6.2.  AES-CTR . . . . . . . . . . . . . . . . . . . . . . . . .  21
       6.2.1.  Introduction  . . . . . . . . . . . . . . . . . . . .  22
       6.2.2.  AES-KW + AES-CTR Example  . . . . . . . . . . . . . .  23
       6.2.3.  ECDH-ES+AES-KW + AES-CTR Example  . . . . . . . . . .  24
   7.  Integrity Check on Encrypted and Decrypted Payloads . . . . .  26
     7.1.  Validating Payload Integrity  . . . . . . . . . . . . . .  26
       7.1.1.  Image Match after Decryption  . . . . . . . . . . . .  27
       7.1.2.  Image Match before Decryption . . . . . . . . . . . .  27
       7.1.3.  Checking Authentication Tag while Decrypting  . . . .  28
     7.2.  Payload Integrity Validation  . . . . . . . . . . . . . .  28
   8.  Firmware Updates on IoT Devices with Flash Memory . . . . . .  30
   9.  Complete Examples . . . . . . . . . . . . . . . . . . . . . .  33
     9.1.  AES Key Wrap Example with Write Directive . . . . . . . .  34
     9.2.  AES Key Wrap Example with Fetch + Copy Directives . . . .  36



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     9.3.  ES-DH Example with Write + Copy Directives  . . . . . . .  42
     9.4.  ES-DH Example with Dependency . . . . . . . . . . . . . .  44
   10. Operational Considerations  . . . . . . . . . . . . . . . . .  48
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  49
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  51
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  51
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  51
     13.2.  Informative References . . . . . . . . . . . . . . . . .  52
   Appendix A.  Full CDDL  . . . . . . . . . . . . . . . . . . . . .  54
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  54
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  54

1.  Introduction

   Vulnerabilities in Internet of Things (IoT) devices have highlighted
   the need for a reliable and secure firmware update mechanism,
   especially for constrained devices.  To protect firmware images, the
   SUIT manifest format was developed [I-D.ietf-suit-manifest].  A
   manifest is a bundle of metadata about the firmware for an IoT
   device, where to find the firmware, and the devices to which it
   applies.  [RFC9124] outlines the necessary information a SUIT
   manifest has to provide.  In addition to protecting against
   modification via digital signatures or message authentication codes,
   the format can also offer confidentiality.

   Encryption prevents third parties, including attackers, from
   accessing the payload.  Attackers often require detailed knowledge of
   a binary, such as a firmware image, to launch successful attacks.
   For instance, return-oriented programming (ROP) [ROP] requires access
   to the binary, and encryption makes writing exploits significantly
   more difficult.  Beyond ensuring the confidentiality of the binary
   itself, protecting the confidentiality of the source code will also
   be necessary to prevent reverse engineering and reproduction of the
   firmware.

   The initial motivation for this document was firmware encryption.
   However, the use of SUIT manifests has expanded to encompass other
   scenarios that require integrity and confidentiality protection,
   including:

   *  Software packages

   *  Personalization and configuration data

   *  Machine learning models






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   These additional use cases stem from the work on Trusted Execution
   Environment Provisioning (TEEP), as detailed in [RFC9397] and
   [I-D.ietf-teep-usecase-for-cc-in-network].  The distinction between
   software and firmware is clarified in [RFC9019].

   For consistency and simplicity, we use the term "payload" generically
   to refer to all objects subject to encryption.

   The payload is encrypted using a symmetric content encryption key,
   which can be established through various mechanisms.  This document
   defines two content key distribution methods for use with the SUIT
   manifest:

   *  Ephemeral-Static (ES) Diffie-Hellman (DH), and

   *  AES Key Wrap (AES-KW).

   The first method relies on asymmetric cryptography, while the second
   uses symmetric cryptography.

   Our design aims to reduce the number of content key distribution
   methods for payload encryption, thereby increasing interoperability
   between different SUIT manifest parser implementations.  The
   mandatory-to-implement algorithms are described in a separate
   document [I-D.ietf-suit-mti].

   The goal of this specification is to protect payloads both during
   end-to-end transport (from the distribution system to the device) and
   at rest when stored on the device.  Constrained devices often employ
   eXecute In Place (XIP), a method of executing code directly from
   flash memory rather than loading it into RAM.  Many of these devices
   lack hardware-based, on-the-fly decryption for code stored in flash
   memory, which may require decrypting and storing firmware images in
   on-chip flash before execution.  However, we expect hardware-based,
   on-the-fly decryption to become more common in the future, enhancing
   confidentiality at rest.

2.  Conventions and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document assumes familiarity with the SUIT manifest
   [I-D.ietf-suit-manifest], the SUIT information model [RFC9124], and
   the SUIT architecture [RFC9019].



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   The following abbreviations are used in this document:

   *  Key Wrap (KW), defined in [RFC3394] (for use with AES)

   *  Key-Encryption Key (KEK) [RFC3394]

   *  Content-Encryption Key (CEK) [RFC5652]

   *  Ephemeral-Static (ES) Diffie-Hellman (DH) [RFC9052]

   *  Authenticated Encryption with Associated Data (AEAD)

   *  Execute in Place (XIP)

   The terms sender and recipient have the following meaning:

   *  Sender: Entity that sends an encrypted payload.

   *  Recipient: Entity that receives an encrypted payload.

   Additionally, we introduce the term "distribution system" (or
   distributor) to refer to an entity that knows the recipients of
   payloads.  It is important to note that the distribution system is
   far more than a file server.  For use of encryption, the distribution
   system either knows the public key of the recipient (for ES-DH), or
   the KEK (for AES-KW).

   The author, which is responsible for creating the payload, does not
   know the recipients.  The author may, for example, be a developer
   building a firmware image.

   The author and the distribution system are logical roles.  In some
   deployments these roles are separated in different physical entities
   and in others they are co-located.

3.  Architecture

   [RFC9019] outlines the architecture for distributing payloads and
   manifests from an author to devices.  However, it does not cover
   payload encryption in detail.  This document extends that
   architecture to support encryption, as illustrated in Figure 1.

   To encrypt a payload, it is essential to know the recipient.  For
   AES-KW, the Key Encryption Key (KEK) must be known, and for ES-DH,
   the sender needs access to the recipient's public key.  This public
   key and its associated parameters may be found in the recipient's
   X.509 certificate [RFC5280].  For authentication and integrity
   protection, recipients must be provisioned with a trust anchor when



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   the manifest is protected by a digital signature.  If a MAC is used
   for manifest protection, a symmetric key must be shared between the
   recipient and the sender.

   With encryption, the author cannot simply create and sign a manifest
   for the payload, as the recipients are often unknown.  Therefore, the
   author must collaborate with the distribution system.  The degree of
   this collaboration is discussed below.

   The primary purpose of encryption is to protect against adversaries
   along the path between the distribution system and the device.  There
   is also a risk that adversaries may extract the decrypted firmware
   image from the device itself.  Consequently, the device must be
   safeguarded against physical attacks.  Such countermeasures are
   outside the scope of this specification.

   Note: It is assumed that a mutually authenticated communication
   channel with integrity and confidentiality protection exists between
   the author and the distribution system.  For example, the author
   could upload the manifest and firmware image to the distribution
   system via a mutually authenticated HTTPS REST API.

    +----------+
    |  Device  |                              +----------+
    |    1     |<--+                          |  Author  |
    |          |   |                          +----+-----+
    +----------+   |                               |
                   |                               | Payload +
                   |                               | Manifest
                   |                               v
    +----------+   |                        +--------------+
    |  Device  |   |  Payload + Manifest    | Distribution |
    |    2     |<--+------------------------+    System    |
    |          |   |                        +--------------+
    +----------+   |
                   |
         ...       |
                   |
    +----------+   |
    |  Device  |   |
    |    n     |<--+
    |          |
    +----------+

     Figure 1: Architecture for the distribution of Encrypted Payloads.

   When the author delegates encryption rights to the distributor, two
   models are possible:



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   1.  Replacing the COSE_Encrypt and Re-signing the Manifest: The
       distributor replaces the COSE_Encrypt structure in the manifest
       and then signs the manifest again.  However, since the
       COSE_Encrypt structure is within a signed container, this
       presents a challenge: replacing COSE_Encrypt alters the digest of
       the manifest, thereby invalidating the signature.  As a result,
       the distributor must be able to sign the new manifest.  If this
       is the case, the distributor gains the authority to construct and
       sign manifests, effectively allowing them to sign code and giving
       them full control over the recipient.  Distributors typically
       perform re-encryption online to manage large numbers of devices
       efficiently, which prevents air-gapping the signing operations.
       This approach necessitates the secure storage of signing keys, as
       outlined in Section 4.3.17 and Section 4.3.18 of [RFC9124].
       Despite these issues, this model represents the current standard
       practice for IoT firmware updates.

   2.  Two-Layer Manifest System: The distributor creates a new manifest
       that overrides the COSE_Encrypt using the dependency system
       defined in [I-D.ietf-suit-trust-domains].  This method introduces
       additional overhead, including one more signature verification,
       one extra manifest, and the need for extra mechanisms on the
       recipient side to handle dependency processing.  While this adds
       complexity, it also enhances security.

   These two models offer different threat profiles for the distributor.
   If the distributor is limited to encryption rights, an attacker who
   breaches the distributor can only launch a limited attack by
   encrypting a modified binary.  However, recipients will detect the
   attack during the image digest check and immediately revert to the
   correct image.

   It is RECOMMENDED that distributors adopt the two-layer manifest
   approach to distribute content encryption keys without re-signing the
   manifest, despite the added complexity and the increased number of
   signature verifications required on the recipient side.

4.  Encryption Extensions

   Extending the SUIT manifest to support payload encryption requires
   minimal changes and is achieved by adding the suit-parameter-
   encryption-info field to the SUIT_Parameters structure, as
   illustrated in Figure 2.  When the suit-parameter-encryption-info is
   included, the manifest processor will attempt to decrypt data during
   copy or write operations.






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   The SUIT_Encryption_Info structure contains the content key
   distribution information.  The details of the SUIT_Encryption_Info
   structure are provided in Section 5.1 (for AES-KW) and Section 5.2
   (for ES-DH).

   SUIT_Parameters //= (suit-parameter-encryption-info
       => bstr .cbor SUIT_Encryption_Info)

   suit-parameter-encryption-info = TBD19

              Figure 2: CDDL of the SUIT_Parameters Extension.

   RFC Editor's Note (TBD19): The value for the suit-parameter-
   encryption-info parameter is set to 19, as the proposed value.

   Once a CEK is available, the steps outlined in Section 6 apply to
   both content key distribution methods described in this section.

   When used with the "Directive Write" and "Directive Copy" directives,
   the SUIT_Encryption_Info structure MUST be included in either the
   suit-directive-override-parameters or the suit-directive-set-
   parameters.  An implementation conforming to this specification MUST
   support both of these parameters.

4.1.  Directive Write

   An author uses the Directive Write (suit-directive-write) to decrypt
   the content specified by suit-parameter-content using suit-parameter-
   encryption-info.  This directive is used to write a specific data
   directly to a component.

   Figure 3 illustrates an example of the Directive Write, which is
   described in the CDDL in Figure 2.  The encrypted payload specified
   by parameter-content, represented as h'EA1...CED' in the example, is
   decrypted using the SUIT_Encryption_Info structure referenced by
   parameter-encryption-info, i.e., h'D86...1F0' in L3.  The resulting
   plaintext payload is then stored in component #0, which is the
   default if no specific component is explicitly designated.

   /  1/  / directive-override-parameters / 20, {
   /  2/    / parameter-content / 18: h'EA1...CED',
   /  3/    / parameter-encryption-info / TBD19: h'D86...1F0'
   /  4/  },
   /  5/  / directive-write / 18, 15

        Figure 3: Example showing the extended suit-directive-write.





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   RFC Editor's Note (TBD19): The value for the parameter-encryption-
   info parameter is set to 19, as the proposed value.

4.2.  Directive Copy

   An author uses the Directive Copy (suit-directive-copy) to decrypt
   the content of the component specified by suit-parameter-source-
   component using suit-parameter-encryption-info.  This directive is
   used to copy data from one component to another.

   Figure 4 illustrates the Directive Copy.  In this example the
   encrypted payload is found at the URI indicated by the parameter-uri,
   i.e., "coaps://example.com/encrypted.bin" in L3.  The encrypted
   payload will be downloaded and stored in component #1, as indicated
   by directive-set-component-index in L1.

   Then, the information in the SUIT_Encryption_Info structure referred
   to by parameter-encryption-info, i.e., h'D86...1F0' in L9, will be
   used to decrypt the content in component #1 and the resulting
   plaintext payload will be stored into component #0 (as set in L7).
   The command in L12 invokes the operation.

   /  1/  / directive-set-component-index / 12, 1,
   /  2/  / directive-override-parameters / 20, {
   /  3/    / parameter-uri / 21: "coaps://example.com/encrypted.bin",
   /  4/   },
   /  5/  / directive-fetch / 21, 15,
   /  6/
   /  7/  / directive-set-component-index / 12, 0,
   /  8/  / directive-override-parameters / 20, {
   /  9/    / parameter-encryption-info / TBD19: h'D86...1F0',
   / 10/    / parameter-source-component / 22: 1
   / 11/  },
   / 12/  / directive-copy / 22, 15

        Figure 4: Example showing the extended suit-directive-copy.

   RFC Editor's Note (TBD19): The value for the suit-parameter-
   encryption-info parameter is set to 19, as the proposed value.

4.3.  Authenticating the Payload

   The payload to be encrypted MAY be detached and, in that case, it is
   not covered by the digital signature or the MAC protecting the
   manifest.  (To be more precise, the suit-authentication-wrapper found
   in the envelope contains a digest of the manifest in the SUIT Digest
   Container.)




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   The lack of authentication and integrity protection of the payload is
   particularly a concern when a cipher without integrity protection is
   used.

   To provide authentication and integrity protection of the payload in
   the detached case a SUIT Digest Container with the hash of the
   encrypted and/or plaintext payload MUST be included in the manifest.
   See suit-parameter-image-digest parameter in Section 8.4.8.6 of
   [I-D.ietf-suit-manifest].

   Once a CEK is available, the steps described in Section 6 are
   applicable.  These steps apply to both content key distribution
   methods.

   More detailed examples for the two directives can be found in
   Section 9.1.

5.  Content Key Distribution

   The following sub-sections describe two content key distribution
   methods: AES Key Wrap (AES-KW) and Ephemeral-Static Diffie-Hellman
   (ES-DH).  While many other methods are specified in the literature
   and supported by COSE, AES-KW and ES-DH were chosen for their
   widespread use in the market today.  They were selected for their
   maturity, differing security properties, and strong interoperability.

   Interoperability requirements for content key distribution methods
   differ: since a device typically supports only one of the two
   specified methods, the distribution system must be aware of the
   supported method.  Restricting a constrained device to a single
   content key distribution method also helps minimize code size.

   Both content key distribution methods require the CEKs to be randomly
   generated.  The guidelines for random number generation in [RFC8937]
   MUST be followed.

   When sending an encrypted payload to multiple recipients, various
   deployment options are available.  The following notation is used to
   explain these options:

     - KEK[R1, S] refers to a KEK shared between recipient R1 and
       the sender S.
     - CEK[R1, S] refers to a CEK shared between R1 and S.
     - CEK[*, S] or KEK[*, S] are used when a single CEK or a single
       KEK is shared with all authorized recipients by a given sender
       S in a certain context.
     - ENC(plaintext, k) refers to the encryption of plaintext with
       a key k.



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5.1.  Content Key Distribution with AES Key Wrap

5.1.1.  Introduction

   The AES Key Wrap (AES-KW) algorithm, as described in [RFC3394], is
   used to encrypt a randomly generated content-encryption key (CEK)
   with a pre-shared key-encryption key (KEK).  The COSE conventions for
   using AES-KW are specified in Section 8.5.2 of [RFC9052] and in
   Section 6.2.1 of [RFC9053].  The encrypted CEK is carried within the
   COSE_recipient structure , which includes the necessary information
   for AES-KW.  The COSE_recipient structure, a substructure of
   COSE_Encrypt, contains the CEK encrypted by the KEK.

   To ensure high security when using AES Key Wrap, it is important that
   the KEK is of high entropy and that implementations protect the KEK
   from disclosure.  A compromised KEK could expose all data encrypted
   with it, including binaries and configuration data.

   The COSE_Encrypt structure conveys the information needed to encrypt
   the payload, including details such as the algorithm and IV.  Even
   though the payload may be conveyed as detached content, the
   encryption information is still embedded in the
   COSE_Encrypt.ciphertext structure.

5.1.2.  Deployment Options

   There are three deployment options for use with AES Key Wrap for
   payload encryption:

   *  If all recipients (typically of the same product family) share the
      same KEK, a single COSE_recipient structure contains the encrypted
      CEK.  The sender executes the following steps:

        1. Fetch KEK[*, S]
        2. Generate CEK
        3. ENC(CEK, KEK)
        4. ENC(payload, CEK)

   This deployment option is strongly discouraged.  An attacker gaining
   access to the KEK will be able to encrypt and send payloads to all
   recipients configured to use this KEK.

   *  If recipients have different KEKs, then multiple COSE_recipient
      structures are included but only a single CEK is used.  Each
      COSE_recipient structure contains the CEK encrypted with the KEKs
      appropriate for a given recipient.  The benefit of this approach
      is that the payload is encrypted only once with a CEK while there
      is no sharing of the KEK across recipients.  Hence, authorized



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      recipients still use their individual KEK to decrypt the CEK and
      to subsequently obtain the plaintext.  The steps taken by the
      sender are:

       1.  Generate CEK
       2.  for i=1 to n
           {
       2a.    Fetch KEK[Ri, S]
       2b.    ENC(CEK, KEK[Ri, S])
           }
       3.  ENC(payload, CEK)

   *  The third option is to use different CEKs encrypted with KEKs of
      authorized recipients.  This approach is appropriate when no
      benefits can be gained from encrypting and transmitting payloads
      only once.  Assume there are n recipients with their unique KEKs -
      KEK[R1, S], ..., KEK[Rn, S] and unique CEKs.  The sender needs to
      execute the following steps:

       1.  for i=1 to n
           {
       1a.    Fetch KEK[Ri, S]
       1b.    Generate CEK[Ri, S]
       1c.    ENC(CEK[Ri, S], KEK[Ri, S])
       1d.    ENC(payload, CEK[Ri, S])
       2.  }

5.1.3.  The CDDL of SUIT_Encryption_Info for AES-KW binary

   The CDDL for the AES-KW binary is shown in Figure 5.
   empty_or_serialized_map and header_map are structures defined in
   [RFC9052].



















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   SUIT_Encryption_Info_AESKW = #6.96([
     protected   : outer_header_map_protected,
     unprotected : outer_header_map_unprotected,
     ciphertext  : bstr / nil,
     recipients  : [ + COSE_recipient_AESKW ]
   ])

   outer_header_map_protected = empty_or_serialized_map
   outer_header_map_unprotected = header_map

   COSE_recipient_AESKW = [
     protected   : bstr .size 0 / bstr .cbor empty_map,
     unprotected : recipient_header_unpr_map_aeskw,
     ciphertext  : bstr        ; CEK encrypted with KEK
   ]

   empty_map = {}

   recipient_header_unpr_map_aeskw =
   {
     ? 1 => int / tstr,  ; content encryption algorithm identifier
     ? 4 => bstr,        ; identifier of the KEK
                         ; pre-shared with the recipient
     * label => values   ; extension point
   }

          Figure 5: CDDL for AES-KW-based Content Key Distribution

   Note that the AES-KW algorithm, as defined in Section 2.2.3.1 of
   [RFC3394], does not have public parameters that vary on a per-
   invocation basis.  Hence, the protected header in the COSE_recipient
   structure is a byte string of zero length.

5.2.  Content Key Distribution with Ephemeral-Static Diffie-Hellman

5.2.1.  Introduction

   Ephemeral-Static Diffie-Hellman (ES-DH) is a public key encryption
   scheme that enables encryption using the recipient's public key.
   There are several variations of this scheme; this document adopts the
   version specified in Section 8.5.5 of [RFC9052].

   The structure is composed of two layers:

   *  Layer 0: Contains content encrypted with a Content Encryption Key
      (CEK).  The content may be provided separately.





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   *  Layer 1: Uses the AES Key Wrap (AES-KW) algorithm to encrypt the
      randomly generated CEK with a Key Encryption Key (KEK) derived via
      ES-DH.  The resulting symmetric key is processed through an HKDF-
      based key derivation function [RFC5869].

   This two-layer structure combines ES-DH with AES-KW and HKDF,
   referred to as ECDH-ES + AES-KW.  An example can be found in
   Figure 10.

   Another variant of the ES-DH algorithm, called ECDH-ES + HKDF, does
   not utilize AES Key Wrap.  However, this version is not covered in
   this document.

5.2.2.  Deployment Options

   This approach supports only two deployment options, as it assumes
   that each recipient is always equipped with a device-specific public/
   private key pair.

   *  When a sender transmits a payload to multiple recipients, all
      recipients receive the same encrypted payload, meaning the same
      CEK is used to encrypt the content.  For each recipient, a
      separate COSE_recipient structure is used, which contains the CEK
      encrypted with the recipient-specific KEK.  To derive the KEK,
      each COSE_recipient structure includes a COSE_recipient_inner
      structure that carries the sender's ephemeral key and an
      identifier for the recipient's public key.

   The steps taken by the sender are:

       1.  Generate CEK
       2.  for i=1 to n
           {
       2a.     Generate KEK[Ri, S] using ES-DH
       2b.     ENC(CEK, KEK[Ri, S])
           }
       3.  ENC(payload,CEK)

   *  The alternative is to encrypt each device specific payload with a
      unique content encryption key (CEK), resulting in a manifest per
      device specific payload. his approach is useful when payloads
      contain device-specific information or when the optimization in
      previous approach are not applicable or not valuable enough.  In
      this case, the encryption operation becomes ENC(payload_i, CEK[Ri,
      S]) where each recipient Ri receives a unique CEK.  Assume that
      KEK[R1, S],..., KEK[Rn, S] have been generated for the recipients
      using ES-DH.  The sender must then follow these steps:




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       1.  for i=1 to n
           {
       1a.     Generate KEK[Ri, S] using ES-DH
       1b.     Generate CEK[Ri, S]
       1c.     ENC(CEK[Ri, S], KEK[Ri, S])
       1d.     ENC(payload, CEK[Ri, S])
           }

5.2.3.  The CDDL of SUIT_Encryption_Info for ES-DH binary

   The CDDL for the ECDH-ES+AES-KW binary is provided in Figure 6.  Only
   the essential parameters are included.  The structures
   empty_or_serialized_map and header_map are defined in [RFC9052].

   SUIT_Encryption_Info_ESDH = #6.96([
     protected   : outer_header_map_protected,
     unprotected : outer_header_map_unprotected,
     ciphertext  : bstr / nil,
     recipients  : [ + COSE_recipient_ESDH ]
   ])

   outer_header_map_protected = empty_or_serialized_map
   outer_header_map_unprotected = header_map

   COSE_recipient_ESDH = [
     protected   : bstr .cbor recipient_header_map_esdh,
     unprotected : recipient_header_unpr_map_esdh,
     ciphertext  : bstr        ; CEK encrypted with KEK
   ]

   recipient_header_map_esdh =
   {
     ?  1 => int / tstr, ; content encryption algorithm identifier
     * label => values   ; extension point
   }

   recipient_header_unpr_map_esdh =
   {
     ? 4 => bstr,        ; identifier of the recipient public key
      -1 => COSE_Key,    ; ephemeral public key for the sender
     * label => values   ; extension point
   }

          Figure 6: CDDL for ES-DH-based Content Key Distribution

   See Section 6 for a description on how to encrypt the payload.





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5.2.4.  Context Information Structure

   The context information structure ensures that the derived keying
   material is "bound" to the specific context of the transaction.  This
   specification reuses the structure defined in Section 5.2 of
   [RFC9053], with modifications to fit the current use case.

   The following elements are bound to the context:

   *  the protocol employing the key-derivation method,

   *  information about the utilized AES Key Wrap algorithm, and the key
      length.

   *  the protected header field, which contains the content key
      encryption algorithm.

   The sender and recipient identities are left empty.

   The following fields in Figure 7 require an explanation:

   *  The COSE_KDF_Context.AlgorithmID field MUST contain the identifier
      for the AES Key Wrap algorithm being used.  This specification
      uses the following values: A128KW (value -3), A192KW (value -4),
      or A256KW (value -5)

   *  The COSE_KDF_Context.SuppPubInfo.keyDataLength field MUST specify
      the key length, in bits, corresponding to the algorithm in the
      AlgorithmID field.  For A128KW the value is 128, for A192KW the
      value is 192, and for A256KW the value 256.

   *  The COSE_KDF_Context.SuppPubInfo.other field captures the protocol
      that uses the ES-DH content key distribution algorithm.  It MUST
      be set to the constant string "SUIT Payload Encryption".

   *  The COSE_KDF_Context.SuppPubInfo.protected field MUST contain the
      serialized content of the recipient_header_map_esdh field, which
      contains (among other elements) the identifier of the content key
      distribution method.












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   COSE_KDF_Context = [
       AlgorithmID : int,
       PartyUInfo : [ PartyInfoSender ],
       PartyVInfo : [ PartyInfoRecipient ],
       SuppPubInfo : [
           keyDataLength : uint,
           protected : bstr,
           other: 'SUIT Payload Encryption'
       ],
       ? SuppPrivInfo : bstr
   ]

   PartyInfoSender = (
       identity : nil,
       nonce : nil,
       other : nil
   )

   PartyInfoRecipient = (
       identity : nil,
       nonce : nil,
       other : nil
   )

               Figure 7: CDDL for COSE_KDF_Context Structure

   The HKDF-based key derivation function MAY contain a salt value, as
   described in Section 5.1 of [RFC9053].  This optional value
   influences the key generation process, though this specification does
   not require the use of a salt.  If the salt is public and included in
   the message, the "salt" algorithm header parameter MUST be used.  The
   salt adds extra randomness to the KDF context.  When the salt is
   transmitted via the "salt" algorithm header parameter, the receiver
   MUST be capable of processing it and MUST pass it into the key
   derivation function.  For more details on salt usage, refer to
   [RFC5869] and NIST SP800-56 [SP800-56].

   Profiles of this specification MAY define an extended version of the
   context information structure or MAY employ a different context
   information structure.

6.  Content Encryption

   This section summarizes the steps involved in content encryption,
   applicable to both content key distribution methods.






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   When using AEAD ciphers, such as AES-GCM or ChaCha20/Poly1305, the
   COSE specification requires a consistent byte stream to create the
   authenticated data structure.  This structure is illustrated in
   Figure 8 and defined in Section 5.3 of [RFC9052].

    Enc_structure = [
      context : "Encrypt",
      protected : empty_or_serialized_map,
      external_aad : bstr
    ]

              Figure 8: CDDL for Enc_structure Data Structure

   This Enc_structure must be populated as follows:

   *  The protected field in the Enc_structure from Figure 8 refers to
      the content of the protected field in the COSE_Encrypt structure.

   *  The value of external_aad MUST be set to a zero-length byte
      string, represented as h'' in diagnostic notation and encoded as
      0x40.

   Some ciphers, such as AES-CTR, provide confidentiality without
   integrity protection (see [RFC9459]).  For these ciphers, the
   Enc_structure shown in Figure 8 cannot be used, as the Additional
   Authenticated Data (AAD) byte string is only applicable to AEAD
   ciphers.  Therefore, the AAD structure is not passed to the API for
   these ciphers, and the protected header in the SUIT_Encryption_Info
   structure MUST be a zero-length byte string.

6.1.  AES-GCM

6.1.1.  Introduction

   AES-GCM is an AEAD cipher and provides confidentiality and integrity
   protection.

   Examples in this section use the following parameters:

   *  Algorithm for payload encryption: AES-GCM-128

      -  k: h'15F785B5C931414411B4B71373A9C0F7'

      -  IV: h'F14AAB9D81D51F7AD943FE87AF4F70CD'

   *  Plaintext: "This is a real firmware image."





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      -  in hex:
         546869732069732061207265616C206669726D7761726520696D6167652E

6.1.2.  AES-KW + AES-GCM Example

   This example uses the following parameters:

   *  Algorithm id for key wrap: A128KW

   *  KEK COSE_Key (Secret Key):

      -  kty: Symmetric

      -  k: 'aaaaaaaaaaaaaaaa'

      -  kid: 'kid-1'

   The COSE_Encrypt structure, in hex format, is (with a line break
   inserted):

   D8608443A10101A1054CF14AAB9D81D51F7AD943FE87F6818340A2012204
   456B69642D31581875603FFC9518D794713C8CA8A115A7FB32565A6D5953
   4D62

   The resulting COSE_Encrypt structure in a diagnostic format is shown
   in Figure 9.

   96([
     / protected: / << {
       / alg / 1: 1 / A128GCM /
     } >>,
     / unprotected: / {
       / IV / 5: h'F14AAB9D81D51F7AD943FE87'
     },
     / ciphertext: / null / detached ciphertext /,
     / recipients: / [
       [
         / protected: / h'',
         / unprotected: / {
           / alg / 1: -3 / A128KW /,
           / kid / 4: 'kid-1'
         },
         / ciphertext: /
           h'75603FFC9518D794713C8CA8A115A7FB32565A6D59534D62'
           / CEK encrypted with KEK /
       ]
     ]
   ])



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              Figure 9: COSE_Encrypt Example for AES Key Wrap

   The encrypted payload (with a line feed added) was:

   758C4B7BBAE2C4C1D462423E0F0DC3164FFA7B85BB94D4BD6D7ED26AB32F
   EB063385D4D3465927EC82CB5E198A59

6.1.3.  ECDH-ES+AES-KW + AES-GCM Example

   This example uses the following parameters:

   *  Algorithm for content key distribution: ECDH-ES + A128KW

   *  KEK COSE_Key (Receiver's Private Key):

      -  kty: EC2

      -  crv: P-256

      -  x: h'5886CD61DD875862E5AAA820E7A15274C968A9BC96048DDCACE32F50C3
         651BA3'

      -  y: h'9EED8125E932CD60C0EAD3650D0A485CF726D378D1B016ED4298B2961E
         258F1B'

      -  d: h'60FE6DD6D85D5740A5349B6F91267EEAC5BA81B8CB53EE249E4B4EB102
         C476B3'

      -  kid: 'kid-2'

   *  KDF Context

      -  Algorithm ID: -3 (A128KW)

      -  SuppPubInfo

         o  keyDataLength: 128

         o  protected: << { / alg / 1: -29 / ECDH-ES+A128KW / } >>

         o  other: 'SUIT Payload Encryption'

   The COSE_Encrypt structure, in hex format, is (with a line break
   inserted):







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   D8608443A10101A1054CF14AAB9D81D51F7AD943FE87F6818344A101381C
   A120A40102200121582073024F415AA51529A66CCEFD88F3F62A734492FF
   45F6AD37FD2888E73EAF19DA2258204005B48A6FD091AA6ABFE3CFBEEDE8
   8B347E521D43405FDBD7D2CFF0EBC21B265818A06B8E6550F308712B1DF0
   44B21B7D11D9B22792F1DE0997

   The resulting COSE_Encrypt structure in a diagnostic format is shown
   in Figure 10.

   96([
     / protected: / << {
       / alg / 1: 1 / A128GCM /
     } >>,
     / unprotected: / {
       / IV / 5: h'F14AAB9D81D51F7AD943FE87'
     },
     / ciphertext: / null / detached ciphertext /,
     / recipients: / [
       [
         / protected: / << {
           / alg / 1: -29 / ECDH-ES + A128KW /
         } >>,
         / unprotected: / {
           / ephemeral key / -1: {
             / kty / 1: 2 / EC2 /,
             / crv / -1: 1 / P-256 /,
             / x / -2: h'73024F415AA51529A66CCEFD88F3F62A
                         734492FF45F6AD37FD2888E73EAF19DA',
             / y / -3: h'4005B48A6FD091AA6ABFE3CFBEEDE88B
                         347E521D43405FDBD7D2CFF0EBC21B26'
           }
         },
         / ciphertext: /
           h'A06B8E6550F308712B1DF044B21B7D11D9B22792F1DE0997'
           / CEK encrypted with KEK /
       ]
     ]
   ])

                 Figure 10: COSE_Encrypt Example for ES-DH

   The encrypted payload (with a line feed added) was:

   758C4B7BBAE2C4C1D462423E0F0DC3164FFA7B85BB94D4BD6D7ED26AB32F
   EB063385D4D3465927EC82CB5E198A59

6.2.  AES-CTR




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6.2.1.  Introduction

   AES-CTR is a non-AEAD cipher that provides confidentiality but lacks
   integrity protection.  Unlike AES-CBC, AES-CTR uses an IV per block,
   as shown in Figure 11.  Hence, when an image is encrypted using AES-
   CTR-128 or AES-CTR-256, the counter value MUST start with the IV
   value and incremented by one for each 16-byte plaintext block.  The
   IV value MAY be provided by the COSE header field or is communicated
   via out-of-band means, for example by setting it to a given value
   (e.g. the value of zero).  Firmware authors MUST make sure that the
   same IV and AES content key encryption combination is not used more
   than once.  Communicating the IV value inside the COSE header is
   RECOMMENDED.

   The following abbreviations are used in Figure 11:

   *  Pi = Plaintext blocks

   *  Ci = Ciphertext blocks

   *  E = Encryption function

   *  k = Symmetric key

   *  ⊕ = XOR operation

            IV1            IV2
             |              |
             |              |
             |              |
         +---+---+      +---+---+
         |       |      |       |
         |       |      |       |
      k--+   E   |   k--+   E   |
         |       |      |       |
         +---+---+      +---+---+
             |              |
        P1---⊕         P2---⊕
             |              |
             |              |
             C1             C2

                        Figure 11: AES-CTR Operation

   Examples in this section use the following parameters:

   *  Algorithm for payload encryption: AES-CTR-128




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      -  k: h'261DE6165070FB8951EC5D7B92A065FE'

      -  IV: h'DAE613B2E0DC55F4322BE38BDBA9DC68'

   *  Plaintext: "This is a real firmware image."

      -  in hex:
         546869732069732061207265616C206669726D7761726520696D6167652E

6.2.2.  AES-KW + AES-CTR Example

   This example uses the following parameters:

   *  Algorithm id for key wrap: A128KW

   *  KEK COSE_Key (Secret Key):

      -  kty: Symmetric

      -  k: 'aaaaaaaaaaaaaaaa'

      -  kid: 'kid-1'

   The COSE_Encrypt structure, in hex format, is (with a line break
   inserted):

   D8608440A20139FFFD0550DAE613B2E0DC55F4322BE38BDBA9DC68F68183
   40A2012204456B69642D315818CE34035CE5C2E2666E46D4C131FC561DD1
   90A6D26CFA1990

   The resulting COSE_Encrypt structure in a diagnostic format is shown
   in Figure 12.



















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   96([
     / protected: / h'',
     / unprotected: / {
       / alg / 1: -65534 / A128CTR /,
       / IV / 5: h'DAE613B2E0DC55F4322BE38BDBA9DC68'
     },
     / ciphertext: / null / detached ciphertext /,
     / recipients: / [
       [
         / protected: / h'',
         / unprotected: / {
           / alg / 1: -3 / A128KW /,
           / kid / 4: 'kid-1'
         },
         / ciphertext: /
           h'CE34035CE5C2E2666E46D4C131FC561DD190A6D26CFA1990'
           / CEK encrypted with KEK /
       ]
     ]
   ])

              Figure 12: COSE_Encrypt Example for AES Key Wrap

   The encrypted payload (with a line feed added) was:

   2BB8DB522AE978246CC775C3B0241BD4B0333FFDD2DB70C7EE7A4966E3B7

6.2.3.  ECDH-ES+AES-KW + AES-CTR Example

   This example uses the following parameters:

   *  Algorithm for content key distribution: ECDH-ES + A128KW

   *  KEK COSE_Key (Receiver's Private Key):

      -  kty: EC2

      -  crv: P-256

      -  x: h'5886CD61DD875862E5AAA820E7A15274C968A9BC96048DDCACE32F50C3
         651BA3'

      -  y: h'9EED8125E932CD60C0EAD3650D0A485CF726D378D1B016ED4298B2961E
         258F1B'

      -  d: h'60FE6DD6D85D5740A5349B6F91267EEAC5BA81B8CB53EE249E4B4EB102
         C476B3'




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      -  kid: 'kid-2'

   *  KDF Context

      -  Algorithm ID: -3 (A128KW)

      -  SuppPubInfo

         o  keyDataLength: 128

         o  protected: << { / alg / 1: -29 / ECDH-ES+A128KW / } >>

         o  other: 'SUIT Payload Encryption'

   The COSE_Encrypt structure, in hex format, is (with a line break
   inserted):

   D8608440A20139FFFD0550DAE613B2E0DC55F4322BE38BDBA9DC68F68183
   44A101381CA120A401022001215820EE0718F6B019C29CC611C18CEDE221
   4066DDCEDC2F0DBEF873CB224C715C1174225820279F2A88E4AB9E2ED30C
   0FCB69515B31B5D36725BFDB9AE02032ED4D5AB52CB85818E28B4502E4F5
   151884A995405579006E9465C3E94E3E0808

   The resulting COSE_Encrypt structure in a diagnostic format is shown
   in Figure 13.


























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   96([
     / protected: / h'',
     / unprotected: / {
       / alg / 1: -65534 / A128CTR /,
       / IV / 5: h'DAE613B2E0DC55F4322BE38BDBA9DC68'
     },
     / ciphertext: / null / detached ciphertext /,
     / recipients: / [
       [
         / protected: / << {
           / alg / 1: -29 / ECDH-ES + A128KW /
         } >>,
         / unprotected: / {
           / ephemeral key / -1: {
             / kty / 1: 2 / EC2 /,
             / crv / -1: 1 / P-256 /,
             / x / -2: h'EE0718F6B019C29CC611C18CEDE22140
                         66DDCEDC2F0DBEF873CB224C715C1174',
             / y / -3: h'279F2A88E4AB9E2ED30C0FCB69515B31
                         B5D36725BFDB9AE02032ED4D5AB52CB8'
           }
         },
         / ciphertext: /
           h'E28B4502E4F5151884A995405579006E9465C3E94E3E0808'
           / CEK encrypted with KEK /
       ]
     ]
   ])

                 Figure 13: COSE_Encrypt Example for ES-DH

   The encrypted payload (with a line feed added) was:

   2BB8DB522AE978246CC775C3B0241BD4B0333FFDD2DB70C7EE7A4966E3B7

7.  Integrity Check on Encrypted and Decrypted Payloads

   In addition to suit-condition-image-match (see Section 8.4.9.2 of
   [I-D.ietf-suit-manifest]), AEAD algorithms used for content
   encryption provides another way to validate the integrity of
   components.  This section provides a guideline to construct secure
   but not redundant SUIT Manifest for encrypted payloads.

7.1.  Validating Payload Integrity

   This sub-section explains three ways to validate the integrity of
   payloads.




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7.1.1.  Image Match after Decryption

   The suit-condition-image-match on the plaintext payload is used after
   decryption.  An example command sequence is shown in Figure 14.

   / directive-set-component-index / 12, 1,
   / directive-override-parameters / 20, {
     / parameter-uri / 21: "coaps://example.com/encrypted.bin"
   },
   / directive-fetch / 21, 15,

   / directive-set-component-index / 12, 0,
   / directive-override-parameters / 20, {
     / parameter-image-digest / 3: << {
       / algorithm-id: / -16 / SHA256 /,
       / digest-bytes: / h'3B1...92A' / digest of plaintext payload /
     } >>,
     / parameter-image-size / 14: 30 / size of plaintext payload /,
     / parameter-encryption-info / TBD19: h'369...50F',
     / parameter-source-component / 22: 1
   },
   / directive-copy / 22, 15,
   / condition-image-match / 3, 15 / check decrypted payload integrity /

               Figure 14: Check Image Match After Decryption

   RFC Editor's Note (TBD19): The value for the suit-parameter-
   encryption-info parameter is set to 19, as the proposed value.

7.1.2.  Image Match before Decryption

   The suit-condition-image-match can also be applied on encrypted
   payloads before decryption takes place.  An example command sequence
   is shown in Figure 15.

   This option mitigates battery exhaustion attacks discussed in
   Section 11.














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  / directive-set-component-index / 12, 1,
  / directive-override-parameters / 20, {
    / parameter-image-digest / 3: << {
      / algorithm-id: / -16 / SHA256 /,
      / digest-bytes: / h'8B4...D34' / digest of encrypted payload /
    } >>,
    / parameter-image-size / 14: 30 / size of encrypted payload /,
    / parameter-uri / 21: "coaps://example.com/encrypted.bin"
  },

  / directive-fetch / 21, 15,
  / condition-image-match / 3, 15 / check decrypted payload integrity /,

  / directive-set-component-index / 12, 0,
  / directive-override-parameters / 20, {
    / parameter-encryption-info / TBD19: h'D86...1F0',
    / parameter-source-component / 22: 1
  },
  / directive-copy / 22, 15

              Figure 15: Check Image Match Before Decryption

   RFC Editor's Note (TBD19): The value for the suit-parameter-
   encryption-info parameter is set to 19, as the proposed value.

7.1.3.  Checking Authentication Tag while Decrypting

   AEAD algorithms, such as AES-GCM and ChaCha20/Poly1305, verify the
   integrity of the encrypted concent.

7.2.  Payload Integrity Validation

   This subsection offers guidelines for validating the integrity of
   payloads within the SUIT manifest.  The decision tree in Figure 16
   illustrates the process for establishing payload integrity.
















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   +------------------------------------------------+
   |        Q1. How is the Payload delivered?       |
   +-+--------------------------------------------+-+
     |                                            |
     | in Content                          others |
     |                                            v
     |             +--------------------------------+
     |             |      Q2. Mitigate Battery      |
     |             |       Exhaustion Attacks?      |
     |             +-+----------------------------+-+
     |               |                            |
     |               | No                     Yes |
     |               v                            |
     | +-----------------------+                  |
     | | Q3. AEAD cipher used? |                  |
     | +----+-------------+----+                  |
     |      |             |                       |
     |      | Yes      No |                       |
     v      v             v                       v
    .+------+.      .-----+-----.      .----------+.
   |   Not    |    |  BEFORE or  |    |   BEFORE    |
   | Required |    |    AFTER    |    | Decryption  |
   |          |    | Decryption  |    |             |
    '--------'      '-----------'      '-----------'

              Figure 16: Decision Tree: Validating the Payload

   There are three questions to ask:

   *  Q1.  How does the recipient receive the encrypted payload?  If the
      encrypted payload is used as the value of the suit-parameter-
      content, its integrity is already verified by the suit-
      authentication-wrapper.  Therefore, no additional integrity check
      is required.  However, if the encrypted payload is delivered via
      suit-directive-fetch from an integrated payload or from outside
      the SUIT envelope, for example "coaps://example.com/
      encrypted.bin", additional considerations must be addressed.

   *  Q2.  Are battery exhaustion attacks a concern?  If yes, the
      integrity of the encrypted payload must be checked before the
      payload is decrypted.  If no, then other questions need to be
      asked.









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   *  Q3.  Is the payload encrypted with an AEAD cipher?  If yes, no
      additional integrity check is required, as the recipient verifies
      the payload's integrity during decryption.  If no, integrity
      validation can occur either before or after decryption.  However,
      validating integrity before decryption is RECOMMENDED especially
      for the AES-CTR mode (see Section 8 of [RFC9459]).

8.  Firmware Updates on IoT Devices with Flash Memory

   Embedded devices come in many forms, and the market is both large and
   fragmented.  As a result, some implementations and deployments may
   adopt firmware update procedures that differ from the descriptions
   provided here.  On a positive note, the SUIT manifest accommodates
   various deployment scenarios, thanks to the "scripting" functionality
   offered by its commands.

   This section specifically addresses firmware images on
   microcontrollers and does not pertain to generic software,
   configuration data, or machine learning models.  The differences
   arise from two main aspects:

   *  Use of Flash Memory: Flash memory in microcontrollers is a type of
      non-volatile memory that typically erases data in larger units
      called blocks, pages, or sectors, and rewrites data at the byte
      level (often 4 bytes) or larger units.  Furthermore, flash memory
      is segmented into different regions, storing the bootloader,
      various versions of firmware images (in designated slots), and
      configuration data.  An example layout of a microcontroller flash
      area is illustrated in Figure 17.

   *  Microcontroller Design: Code on microcontrollers typically cannot
      be executed from arbitrary locations in flash memory without
      additional software development and design efforts.  Consequently,
      developers often compile firmware so that the bootloader can
      execute code from a specific location in flash memory, commonly
      referred to as the "primary slot."

   Once the encrypted firmware image is transferred to the device, it is
   usually stored in a dedicated area known as the "secondary slot."

   During the next boot, the bootloader detects the new firmware image
   and begins decrypting it sector by sector, swapping it with the image
   located in the primary slot.  This method of swapping the newly
   downloaded image with the previously valid one requires two slots,
   allowing for a rollback if the new firmware fails to boot, thereby
   enhancing the robustness of the firmware update process.





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   The swap occurs only after verifying the signature on the plaintext.
   It is important to note that the plaintext firmware image is
   available in the primary slot only after the swap is completed,
   unless "dummy decrypt" is used to compute the hash over the plaintext
   prior to executing the decryption during the swap.  In this context,
   dummy decryption refers to decrypting the firmware image in the
   secondary slot sector by sector while computing a rolling hash over
   the resulting plaintext (also sector by sector) without performing
   the swap operation.  Although performance optimizations, such as
   conveying hashes for each sector in the manifest rather than a hash
   of the entire firmware image, are possible, these optimizations are
   not detailed in this specification.

   Without hardware-based, on-the-fly decryption, the image in the
   primary slot is available in cleartext and may need to be re-
   encrypted before copying it to the secondary slot.  This step might
   be necessary if the secondary slot has different access permissions
   or is located in off-chip flash memory, which tends to be more
   vulnerable to physical attacks.
































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   +--------------------------------------------------+
   | Bootloader                                       |
   +--------------------------------------------------+
   | Primary Slot                                     |
   |                                        (sector 0)|
   |..................................................|
   |                                                  |
   |                                        (sector 1)|
   |..................................................|
   |                                                  |
   |                                        (sector 2)|
   |..................................................|
   |                                                  |
   |                                           ...    |
   +--------------------------------------------------+
   | Secondary Slot                                   |
   |                                        (sector 0)|
   |..................................................|
   |                                                  |
   |                                        (sector 1)|
   |..................................................|
   |                                                  |
   |                                        (sector 2)|
   |..................................................|
   |                                                  |
   |                                           ...    |
   +--------------------------------------------------+
   | Swap Area                                        |
   |                                                  |
   +--------------------------------------------------+
   | Configuration Data                               |
   +--------------------------------------------------+

                    Figure 17: Example Flash Area Layout

   The ability to resume an interrupted firmware update is often
   essential for unattended devices, including low-end, constrained IoT
   devices.  To meet this requirement, a firmware image must be divided
   into sectors, with each sector encrypted individually using a cipher
   that does not increase the size of the resulting ciphertext (i.e., by
   avoiding the addition of an authentication tag after each encrypted
   block).

   If an update is aborted while the bootloader is decrypting the newly
   received image and swapping the sectors, the bootloader can restart
   from where it left off.  This technique enhances robustness and
   performance.




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   For this purpose, ciphers without integrity protection are employed
   to encrypt the firmware image.  It is crucial that integrity
   protection for the firmware image is provided, and the suit-
   parameter-image-digest, defined in Section 8.4.8.6 of
   [I-D.ietf-suit-manifest], MUST be utilized.

   [RFC9459] specifies the AES Counter (AES-CTR) mode and AES Cipher
   Block Chaining (AES-CBC) ciphers, both of which do not provide
   integrity protection.  These ciphers are suitable for firmware
   encryption in IoT devices.  However, for many other scenarios
   involving software packages, configuration information, or
   personalization data, the use of AEAD ciphers is RECOMMENDED.

   The following subsections offer additional information on the
   selection of initialization vectors (IVs) for use with AES-CTR in the
   context of firmware encryption.  A random CEK MUST be used with every
   plaintexts, as specified in Section 5, since the IVs are not random
   but are instead based on the slot/sector combination in flash memory.
   The discussion assumes that the block size of AES is significantly
   smaller than the sector size.  Typically, flash memory sectors are
   measured in KiB, necessitating the decryption of multiple AES blocks
   to complete the decryption of an entire sector.

   To offer a specific example, let us assume the slot size of a
   specific flash controller on an IoT device is 64 KiB, the sector size
   4096 bytes (4 KiB) and an AES plaintext block size of 16 bytes.  The
   counter values used with AES-CTR range from IV+0 to IV+255 in the
   first sector, and 16 * 256 counter values are required for the slot.
   This

   IV value is either communicated in the COSE header or via out-of-band
   means.

9.  Complete Examples

   The following manifests illustrate how to deliver an encrypted
   payload along with its encryption information to devices.

   In the AES-KW examples, HMAC-256 MACs are included, utilizing the
   following secret key:

     'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'
     (616161... in hex, and its length is 32)

   ES-DH examples are signed using the following ECDSA secp256r1 key:






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   -----BEGIN PRIVATE KEY-----
   MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgApZYjZCUGLM50VBC
   CjYStX+09jGmnyJPrpDLTz/hiXOhRANCAASEloEarguqq9JhVxie7NomvqqL8Rtv
   P+bitWWchdvArTsfKktsCYExwKNtrNHXi9OB3N+wnAUtszmR23M4tKiW
   -----END PRIVATE KEY-----

   The corresponding public key can be used to verify these examples:

   -----BEGIN PUBLIC KEY-----
   MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEhJaBGq4LqqvSYVcYnuzaJr6qi/Eb
   bz/m4rVlnIXbwK07HypLbAmBMcCjbazR14vTgdzfsJwFLbM5kdtzOLSolg==
   -----END PUBLIC KEY-----

   Each example uses SHA-256 as the digest function.

9.1.  AES Key Wrap Example with Write Directive

   The following SUIT manifest instructs a parser to authenticate the
   manifest using COSE_Mac0 with HMAC256.  It also directs the parser to
   write and decrypt the encrypted payload into a component using the
   suit-directive-write directive.

   The SUIT manifest in diagnostic notation (with line breaks added for
   clarity) is displayed below:

   /  1/ / SUIT_Envelope_Tagged / 107({
   /  2/   / authentication-wrapper / 2: << [
   /  3/     << [
   /  4/       / digest-algorithm-id: / -16 / SHA256 /,
   /  5/       / digest-bytes: / h'037A5C325CE14078A0AADF007428EAC6
   /  6/                           59361AD9402A732410BDA542FAE94E2C'
   /  7/     ] >>,
   /  8/     << / COSE_Mac0_Tagged / 17([
   /  9/       / protected: / << {
   / 10/         / algorithm-id / 1: 5 / HMAC256 /
   / 11/       } >>,
   / 12/       / unprotected: / {},
   / 13/       / payload: / null,
   / 14/       / tag: / h'8D92599011C451A4C5FB69709FA6CA6C
   / 15/                  0F846D692BDBB3F624EC91F82F9F620A'
   / 16/     ]) >>
   / 17/   ] >>,
   / 18/   / manifest / 3: << {
   / 19/     / manifest-version / 1: 1,
   / 20/     / manifest-sequence-number / 2: 1,
   / 21/     / common / 3: << {
   / 22/       / components / 2: [
   / 23/         ['plaintext-firmware']



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   / 24/       ]
   / 25/     } >>,
   / 26/     / install / 20: << [
   / 27/       / fetch encrypted firmware /
   / 28/       / directive-override-parameters / 20, {
   / 29/         / parameter-content / 18:
   / 30/           h'758C4B7BBAE2C4C1D462423E0F0DC3164FFA7B85BB94D4
   / 31/             BD6D7ED26AB32FEB063385D4D3465927EC82CB5E198A59',
   / 32/         / parameter-encryption-info / 19: << 96([
   / 33/           / protected: / << {
   / 34/             / alg / 1: 1 / A128GCM /
   / 35/           } >>,
   / 36/           / unprotected: / {
   / 37/             / IV / 5: h'F14AAB9D81D51F7AD943FE87'
   / 38/           },
   / 39/           / ciphertext: / null / detached ciphertext /,
   / 40/           / recipients: / [
   / 41/             [
   / 42/               / protected: / h'',
   / 43/               / unprotected: / {
   / 44/                 / alg / 1: -3 / A128KW /,
   / 45/                 / kid / 4: 'kid-1'
   / 46/               },
   / 47/               / ciphertext: /
   / 48/                 h'75603FFC9518D794713C8CA8
   / 49/                   A115A7FB32565A6D59534D62'
   / 50/                 / CEK encrypted with KEK /
   / 51/             ]
   / 52/           ]
   / 53/         ]) >>
   / 54/       },
   / 55/
   / 56/       / decrypt encrypted firmware /
   / 57/       / directive-write / 18, 15
   / 58/         / consumes the SUIT_Encryption_Info above /
   / 59/     ] >>
   / 60/   } >>
   / 61/ })

   In hex format, the SUIT manifest is:











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   D86BA2025853825824822F5820037A5C325CE14078A0AADF007428EAC659
   361AD9402A732410BDA542FAE94E2C582AD18443A10105A0F658208D9259
   9011C451A4C5FB69709FA6CA6C0F846D692BDBB3F624EC91F82F9F620A03
   5898A4010102010357A102818152706C61696E746578742D6669726D7761
   72651458778414A212582E758C4B7BBAE2C4C1D462423E0F0DC3164FFA7B
   85BB94D4BD6D7ED26AB32FEB063385D4D3465927EC82CB5E198A5913583E
   D8608443A10101A1054CF14AAB9D81D51F7AD943FE87F6818340A2012204
   456B69642D31581875603FFC9518D794713C8CA8A115A7FB32565A6D5953
   4D62120F

9.2.  AES Key Wrap Example with Fetch + Copy Directives

   The following SUIT manifest instructs a parser to fetch and store the
   encrypted payload.  Subsequently, the payload is decrypted and copied
   into another component using the suit-directive-copy directive.  This
   approach is particularly effective for constrained devices with
   execute-in-place (XIP) flash memory.

   The SUIT manifest in diagnostic notation (with line breaks added for
   clarity) is displayed below:

   /  1/ / SUIT_Envelope_Tagged / 107({
   /  2/   / authentication-wrapper / 2: << [
   /  3/     << [
   /  4/       / digest-algorithm-id: / -16 / SHA256 /,
   /  5/       / digest-bytes: / h'3C92AECEAA7225DDD5129A83B2842BF2
   /  6/                           8CC53B2C9467C5BF256E7108F2DA7C9C'
   /  7/     ] >>,
   /  8/     << / COSE_Mac0_Tagged / 17([
   /  9/       / protected: / << {
   / 10/         / algorithm-id / 1: 5 / HMAC256 /
   / 11/       } >>,
   / 12/       / unprotected: / {},
   / 13/       / payload: / null,
   / 14/       / tag: / h'46CB34181A04B967023D4C9E136DC5DC
   / 15/                  591D8A9BE9365DE4D282C9D6168C01FB'
   / 16/     ]) >>
   / 17/   ] >>,
   / 18/   / manifest / 3: << {
   / 19/     / manifest-version / 1: 1,
   / 20/     / manifest-sequence-number / 2: 1,
   / 21/     / common / 3: << {
   / 22/       / components / 2: [
   / 23/         ['plaintext-firmware'],
   / 24/         ['encrypted-firmware']
   / 25/       ]
   / 26/     } >>,
   / 27/     / install / 20: << [



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   / 28/       / fetch encrypted firmware /
   / 29/       / directive-set-component-index / 12,
   / 30/         1 / ['encrypted-firmware'] /,
   / 31/       / directive-override-parameters / 20, {
   / 32/         / parameter-image-size / 14: 46,
   / 33/         / parameter-uri / 21:
   / 34/           "coaps://example.com/encrypted-firmware"
   / 35/       },
   / 36/       / directive-fetch / 21, 15,
   / 37/
   / 38/       / decrypt encrypted firmware /
   / 39/       / directive-set-component-index / 12,
   / 40/         0 / ['plaintext-firmware'] /,
   / 41/       / directive-override-parameters / 20, {
   / 42/         / parameter-encryption-info / 19: << 96([
   / 43/           / protected: / << {
   / 44/             / alg / 1: 1 / A128GCM /
   / 45/           } >>,
   / 46/           / unprotected: / {
   / 47/             / IV / 5: h'F14AAB9D81D51F7AD943FE87'
   / 48/           },
   / 49/           / ciphertext: / null / detached ciphertext /,
   / 50/           / recipients: / [
   / 51/             [
   / 52/               / protected: / h'',
   / 53/               / unprotected: / {
   / 54/                 / alg / 1: -3 / A128KW /,
   / 55/                 / kid / 4: 'kid-1'
   / 56/               },
   / 57/               / ciphertext: /
   / 58/                 h'75603FFC9518D794713C8CA8
   / 59/                   A115A7FB32565A6D59534D62'
   / 60/                 / CEK encrypted with KEK /
   / 61/             ]
   / 62/           ]
   / 63/         ]) >>,
   / 64/         / parameter-source-component / 22:
   / 65/           1 / ['encrypted-firmware'] /
   / 66/       },
   / 67/       / directive-copy / 22,
   / 68/         15 / consumes the SUIT_Encryption_Info above /
   / 69/     ] >>
   / 70/   } >>
   / 71/ })







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   The default storage area is defined by the component identifier (see
   Section 8.4.5.1 of [I-D.ietf-suit-manifest]).  In this example, the
   component identifier for component #0 is ['plaintext-firmware'] and
   the file path "/plaintext-firmware" is the expected location.

   While parsing the manifest, the behavior of SUIT manifest processor
   would be

   *  [L2-L17] authenticates the manifest part on [L18-L68]

   *  [L22-L25] gets two component identifiers; ['plaintext-firmware']
      for component #0, and ['encrypted-firmware'] for component # 1
      respectively

   *  [L29] sets current component index # 1 (the lasting directives
      target ['encrypted-firmware'])

   *  [L33-L34] sets source uri parameter "coaps://example.com/
      encrypted-firmware"

   *  [L36] fetches content from source uri into ['encrypted-firmware']

   *  [L39] sets current component index # 0 (the lasting directives
      target ['plaintext-firmware'])

   *  [L42-L62] sets SUIT encryption info parameter

   *  [L63-L64] sets source component index parameter # 1

   *  [L66] decrypts component # 1 (source component index) and stores
      the result into component # 0 (current component index)

   Table 1 lists the features from the SUIT manifest specification,
   which are re-used by this specification.

















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        +===============================+=========+===============+
        | Feature Name                  | Abbr.   | Manifest Ref. |
        +===============================+=========+===============+
        | component identifier          | CI      | Sec. 8.4.5.1  |
        +-------------------------------+---------+---------------+
        | (destination) component index | dst-CI  | Sec. 8.4.10.1 |
        +-------------------------------+---------+---------------+
        | (destination) component slot  | dst-CS  | Sec. 8.4.8.8  |
        | OPTIONAL param                |         |               |
        +-------------------------------+---------+---------------+
        | (source) uri OPTIONAL         | src-URI | Sec. 8.4.8.10 |
        | parameter                     |         |               |
        +-------------------------------+---------+---------------+
        | source component index        | src-CI  | Sec. 8.4.8.11 |
        | OPTIONAL parameter            |         |               |
        +-------------------------------+---------+---------------+

                     Table 1: Example Flash Area Layout

   The resulting state of the SUIT manifest processor is shown in
   Table 2.

    +==============+========================+========================+
    | Abbreviation | Plaintext              | Ciphertext             |
    +==============+========================+========================+
    | CI           | ['plaintext-firmware'] | ['encrypted-firmware'] |
    +--------------+------------------------+------------------------+
    | dst-CI       | 0                      | 1                      |
    +--------------+------------------------+------------------------+
    | dst-CS       | N/A                    | N/A                    |
    +--------------+------------------------+------------------------+
    | src-URI      | N/A                    | "coaps://example.com/  |
    |              |                        | encrypted-firmware"    |
    +--------------+------------------------+------------------------+
    | src-CI       | 1                      | N/A                    |
    +--------------+------------------------+------------------------+

                    Table 2: Manifest Processor State

   In hex format, the SUIT manifest shown above is:











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   D86BA2025853825824822F58203C92AECEAA7225DDD5129A83B2842BF28C
   C53B2C9467C5BF256E7108F2DA7C9C582AD18443A10105A0F6582046CB34
   181A04B967023D4C9E136DC5DC591D8A9BE9365DE4D282C9D6168C01FB03
   58B2A40101020103582BA102828152706C61696E746578742D6669726D77
   6172658152656E637279707465642D6669726D7761726514587C8C0C0114
   A20E182E157826636F6170733A2F2F6578616D706C652E636F6D2F656E63
   7279707465642D6669726D77617265150F0C0014A213583ED8608443A101
   01A1054CF14AAB9D81D51F7AD943FE87F6818340A2012204456B69642D31
   581875603FFC9518D794713C8CA8A115A7FB32565A6D59534D621601160F

   The encrypted payload (with a line feed added) to be fetched from
   "coaps://example.com/encrypted-firmware" is:

   758C4B7BBAE2C4C1D462423E0F0DC3164FFA7B85BB94D4BD6D7ED26AB32F
   EB063385D4D3465927EC82CB5E198A59

   The previous example does not utilize storage slots.  However, it is
   possible to implement this functionality for devices that support
   slots in flash memory.  In the enhanced example below, we reference
   the slots using [h'00'] and [h'01'].  In this context, the component
   identifier [h'00'] designates component slot #0.

   /  1/ / SUIT_Envelope_Tagged / 107({
   /  2/   / authentication-wrapper / 2: << [
   /  3/     << [
   /  4/       / digest-algorithm-id: / -16 / SHA256 /,
   /  5/       / digest-bytes: / h'6D74BD3110A2573236E03DD78693D5B2
   /  6/                           1C299C917A4327D9939DDF3582A41DE3'
   /  7/     ] >>,
   /  8/     << / COSE_Mac0_Tagged / 17([
   /  9/       / protected: / << {
   / 10/         / algorithm-id / 1: 5 / HMAC256 /
   / 11/       } >>,
   / 12/       / unprotected: / {},
   / 13/       / payload: / null,
   / 14/       / tag: / h'E6837A54A9B5813F8D5EDAD48AB96D5D
   / 15/                  7388D9D1C89AB29EC55AE964F67E01ED'
   / 16/     ]) >>
   / 17/   ] >>,
   / 18/   / manifest / 3: << {
   / 19/     / manifest-version / 1: 1,
   / 20/     / manifest-sequence-number / 2: 1,
   / 21/     / common / 3: << {
   / 22/       / components / 2: [
   / 23/         [h'00'],
   / 24/         [h'01']
   / 25/       ]
   / 26/     } >>,



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   / 27/     / install / 20: << [
   / 28/       / fetch encrypted firmware /
   / 29/       / directive-set-component-index / 12, 1 / [h'01'] /,
   / 30/       / directive-override-parameters / 20, {
   / 31/         / parameter-image-size / 14: 46,
   / 32/         / parameter-uri / 21:
   / 33/           "coaps://example.com/encrypted-firmware"
   / 34/       },
   / 35/       / directive-fetch / 21, 15,
   / 36/
   / 37/       / decrypt encrypted firmware /
   / 38/       / directive-set-component-index / 12, 0 / ['00'] /,
   / 39/       / directive-override-parameters / 20, {
   / 40/         / parameter-encryption-info / 19: << 96([
   / 41/           / protected: / << {
   / 42/             / alg / 1: 1 / A128GCM /
   / 43/           } >>,
   / 44/           / unprotected: / {
   / 45/             / IV / 5: h'F14AAB9D81D51F7AD943FE87'
   / 46/           },
   / 47/           / ciphertext: / null / detached ciphertext /,
   / 48/           / recipients: / [
   / 49/             [
   / 50/               / protected: / h'',
   / 51/               / unprotected: / {
   / 52/                 / alg / 1: -3 / A128KW /,
   / 53/                 / kid / 4: 'kid-1'
   / 54/               },
   / 55/               / ciphertext: /
   / 56/                 h'75603FFC9518D794713C8CA8
   / 57/                   A115A7FB32565A6D59534D62'
   / 58/                 / CEK encrypted with KEK /
   / 59/             ]
   / 60/           ]
   / 61/         ]) >>,
   / 62/         / parameter-source-component / 22: 1 / [h'01'] /
   / 63/       },
   / 64/       / directive-copy / 22, 15
   / 65/         / consumes the SUIT_Encryption_Info above /
   / 66/     ] >>
   / 67/   } >>
   / 68/ })









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9.3.  ES-DH Example with Write + Copy Directives

   The following SUIT manifest instructs a parser to authenticate the
   manifest using COSE_Sign1 with ES256.  It also directs the parser to
   write and decrypt the encrypted payload into a component via the
   suit-directive-write directive.

   The SUIT manifest in diagnostic notation (formatted with line breaks
   for clarity) is presented below:

   /  1/ / SUIT_Envelope_Tagged / 107({
   /  2/   / authentication-wrapper / 2: << [
   /  3/     << [
   /  4/       / digest-algorithm-id: / -16 / SHA256 /,
   /  5/       / digest-bytes: / h'1DB69EF1477E9942815F29F78E09957B
   /  6/                           26B4ADD03902BDB3D1EDF3DA2075F593'
   /  7/     ] >>,
   /  8/     << / COSE_Sign1_Tagged / 18([
   /  9/       / protected: / << {
   / 10/         / algorithm-id / 1: -9 / ESP256 /
   / 11/       } >>,
   / 12/       / unprotected: / {},
   / 13/       / payload: / null,
   / 14/       / signature: / h'2B20A797AC7DBEBC53147592BB110AEC
   / 15/                        43A2489AC19A169BB59FF6BD429300A9
   / 16/                        719FEB7DF277E4B8D1D821C816854229
   / 17/                        F266AC62AFD9DB52114F608EE66B187B'
   / 18/     ]) >>
   / 19/   ] >>,
   / 20/   / manifest / 3: << {
   / 21/     / manifest-version / 1: 1,
   / 22/     / manifest-sequence-number / 2: 1,
   / 23/     / common / 3: << {
   / 24/       / components / 2: [
   / 25/         ['decrypted-firmware']
   / 26/       ]
   / 27/     } >>,
   / 28/     / install / 20: << [
   / 29/       / directive-set-component-index / 12,
   / 30/         0 / ['plaintext-firmware'] /,
   / 31/       / directive-override-parameters / 20, {
   / 32/         / parameter-content / 18:
   / 33/           h'758C4B7BBAE2C4C1D462423E0F0DC3164FFA7B85BB94D4
   / 34/             BD6D7ED26AB32FEB063385D4D3465927EC82CB5E198A59',
   / 35/         / parameter-encryption-info / 19: << 96([
   / 36/           / protected: / << {
   / 37/             / alg / 1: 1 / A128GCM /
   / 38/           } >>,



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   / 39/           / unprotected: / {
   / 40/             / IV / 5: h'F14AAB9D81D51F7AD943FE87'
   / 41/           },
   / 42/           / ciphertext: / null / detached ciphertext /,
   / 43/           / recipients: / [
   / 44/             [
   / 45/               / protected: / << {
   / 46/                 / alg / 1: -29 / ECDH-ES + A128KW /
   / 47/               } >>,
   / 48/               / unprotected: / {
   / 49/                 / ephemeral key / -1: {
   / 50/                   / kty / 1: 2 / EC2 /,
   / 51/                   / crv / -1: 1 / P-256 /,
   / 52/                   / x / -2:
   / 53/                     h'73024F415AA51529A66CCEFD88F3F62A
   / 54/                       734492FF45F6AD37FD2888E73EAF19DA',
   / 55/                   / y / -3:
   / 56/                     h'4005B48A6FD091AA6ABFE3CFBEEDE88B
   / 57/                       347E521D43405FDBD7D2CFF0EBC21B26'
   / 58/                 },
   / 59/                 / kid / 4: 'kid-2'
   / 60/               },
   / 61/               / ciphertext: /
   / 62/                 h'A06B8E6550F308712B1DF044
   / 63/                   B21B7D11D9B22792F1DE0997'
   / 64/                 / CEK encrypted with KEK /
   / 65/             ]
   / 66/           ]
   / 67/         ]) >>
   / 68/       },
   / 69/       / directive-write / 18,
   / 70/         15 / consumes the SUIT_Encryption_Info above /
   / 71/     ] >>
   / 72/   } >>
   / 73/ })

   In hex format, the SUIT manifest is this:














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   D86BA2025873825824822F58201DB69EF1477E9942815F29F78E09957B26
   B4ADD03902BDB3D1EDF3DA2075F593584AD28443A10128A0F658402B20A7
   97AC7DBEBC53147592BB110AEC43A2489AC19A169BB59FF6BD429300A971
   9FEB7DF277E4B8D1D821C816854229F266AC62AFD9DB52114F608EE66B18
   7B0358E8A4010102010357A1028181526465637279707465642D6669726D
   776172651458C7860C0014A212582E758C4B7BBAE2C4C1D462423E0F0DC3
   164FFA7B85BB94D4BD6D7ED26AB32FEB063385D4D3465927EC82CB5E198A
   5913588CD8608443A10101A1054CF14AAB9D81D51F7AD943FE87F6818344
   A101381CA220A40102200121582073024F415AA51529A66CCEFD88F3F62A
   734492FF45F6AD37FD2888E73EAF19DA2258204005B48A6FD091AA6ABFE3
   CFBEEDE88B347E521D43405FDBD7D2CFF0EBC21B2604456B69642D325818
   A06B8E6550F308712B1DF044B21B7D11D9B22792F1DE0997120F

9.4.  ES-DH Example with Dependency

   The following SUIT manifest requests a parser to resolve the
   dependency.

   The dependent manifest is signed with another key:

   -----BEGIN EC PRIVATE KEY-----
   MHcCAQEEIIQa67e56m8CYL5zVaJFiLl30j0qxb8ray2DeUMqH+qYoAoGCCqGSM49
   AwEHoUQDQgAEDpCKqPBm2x8ITgw2UsY5Ur2Z8qW9si+eATZ6rQOrpot32hvYrE8M
   tJC6IQZIv3mrFk1JrTVR1x0xSydJ7kLSmg==
   -----END EC PRIVATE KEY-----

   The dependency manifest is embedded as an integrated-dependency and
   referred to by the "#dependency-manifest" URI.

   The SUIT manifest in diagnostic notation (with line breaks added for
   readability) is shown here:

   /  1/ / SUIT_Envelope_Tagged / 107({
   /  2/   / authentication-wrapper / 2: << [
   /  3/     << [
   /  4/       / digest-algorithm-id: / -16 / SHA256 /,
   /  5/       / digest-bytes: / h'A00CB6C85515C1EF471B50B542FACDD8
   /  6/                           8B71B3C7EA2A43DE13D32C4A99056FE9'
   /  7/     ] >>,
   /  8/     << / COSE_Sign1_Tagged / 18([
   /  9/       / protected: / << {
   / 10/         / algorithm-id / 1: -9 / ESP256 /
   / 11/       } >>,
   / 12/       / unprotected: / {},
   / 13/       / payload: / null,
   / 14/       / signature: / h'3000301B7C54B3383CC4723C4B7BE667
   / 15/                        C6760C504213A105DD38401BED5EEF8E
   / 16/                        B915F8313420104F59467D76790A0EA2



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   / 17/                        20B6021B4ED87051B3B4A8D05F7E0254'
   / 18/     ]) >>
   / 19/   ] >>,
   / 20/   / manifest / 3: << {
   / 21/     / manifest-version / 1: 1,
   / 22/     / manifest-sequence-number / 2: 1,
   / 23/     / common / 3: << {
   / 24/       / dependencies / 1: {
   / 25/         / component-index / 1: {
   / 26/           / dependency-prefix / 1: [
   / 27/              'dependency-manifest.suit'
   / 28/           ]
   / 29/         }
   / 30/       },
   / 31/       / components / 2: [
   / 32/         ['decrypted-firmware']
   / 33/       ]
   / 34/     } >>,
   / 35/     / manifest-component-id / 5: [
   / 36/       'dependent-manifest.suit'
   / 37/     ],
   / 38/     / install / 20: << [
   / 39/       / NOTE: set SUIT_Encryption_Info /
   / 40/       / directive-set-component-index / 12,
   / 41/         0 / ['decrypted-firmware'] /,
   / 42/       / directive-override-parameters / 20, {
   / 43/         / parameter-content / 18:
   / 44/           h'758C4B7BBAE2C4C1D462423E0F0DC3164FFA7B85BB94D4
   / 45/             BD6D7ED26AB32FEB063385D4D3465927EC82CB5E198A59',
   / 46/         / parameter-encryption-info / 19: << 96([
   / 47/           / protected: / << {
   / 48/             / alg / 1: 1 / A128GCM /
   / 49/           } >>,
   / 50/           / unprotected: / {
   / 51/             / IV / 5: h'F14AAB9D81D51F7AD943FE87'
   / 52/           },
   / 53/           / ciphertext: / null / detached ciphertext /,
   / 54/           / recipients: / [
   / 55/             [
   / 56/               / protected: / << {
   / 57/                 / alg / 1: -29 / ECDH-ES + A128KW /
   / 58/               } >>,
   / 59/               / unprotected: / {
   / 60/                 / ephemeral key / -1: {
   / 61/                   / kty / 1: 2 / EC2 /,
   / 62/                   / crv / -1: 1 / P-256 /,
   / 63/                   / x / -2:
   / 64/                     h'73024F415AA51529A66CCEFD88F3F62A



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   / 65/                       734492FF45F6AD37FD2888E73EAF19DA',
   / 66/                   / y / -3:
   / 67/                     h'4005B48A6FD091AA6ABFE3CFBEEDE88B
   / 68/                       347E521D43405FDBD7D2CFF0EBC21B26'
   / 69/                 },
   / 70/                 / kid / 4: 'kid-2'
   / 71/               },
   / 72/               / ciphertext: /
   / 73/                 h'A06B8E6550F308712B1DF044
   / 74/                   B21B7D11D9B22792F1DE0997'
   / 75/                 / CEK encrypted with KEK /
   / 76/             ]
   / 77/           ]
   / 78/         ]) >>
   / 79/       },
   / 80/
   / 81/       / NOTE: call dependency-manifest /
   / 82/       / directive-set-component-index / 12,
   / 83/         1 / ['dependenty-manifest.suit'] /,
   / 84/       / directive-override-parameters / 20, {
   / 85/         / parameter-image-digest / 3: << [
   / 86/           / algorithm-id / -16 / SHA256 /,
   / 87/           / digest-bytes / h'4B15C90FBD776A820E7E733DF040D90B
   / 88/                              356B5C75982ECAECE8673818179BDF16'
   / 89/         ] >>,
   / 90/         / parameter-image-size / 14: 247,
   / 91/         / parameter-uri / 21: "#dependency-manifest"
   / 92/       },
   / 93/       / directive-fetch / 21, 15,
   / 94/       / condition-dependency-integrity / 7, 15,
   / 95/       / directive-process-dependency / 11, 15
   / 96/     ] >>
   / 97/   } >>,
   / 98/   "#dependency-manifest": <<
   / 99/     / SUIT_Envelope_Tagged / 107({
   /100/       / authentication-wrapper / 2: << [
   /101/         << [
   /102/           / digest-algorithm-id: / -16 / SHA256 /,
   /103/           / digest-bytes: /
   /104/             h'4B15C90FBD776A820E7E733DF040D90B
   /105/               356B5C75982ECAECE8673818179BDF16'
   /106/         ] >>,
   /107/         << / COSE_Sign1_Tagged / 18([
   /108/           / protected: / << {
   /109/             / algorithm-id / 1: -9 / ESP256 /
   /110/           } >>,
   /111/           / unprotected: / {},
   /112/           / payload: / null,



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   /113/           / signature: / h'BF95C29295B45470EF819E7F4E3C9084
   /114/                            F4534E26469C0A0F2B8B9664881A5359
   /115/                            D500F81BD3A6436A025C3E92E51CD714
   /116/                            8F83DF47D29FF253F8D41B4D350A2B75'
   /117/         ]) >>
   /118/       ] >>,
   /119/       / manifest / 3: << {
   /120/         / manifest-version / 1: 1,
   /121/         / manifest-sequence-number / 2: 1,
   /122/         / common / 3: << {
   /123/           / components / 2: [
   /124/             ['decrypted-firmware']
   /125/           ],
   /126/           / shared-sequence / 4: << [
   /127/             / directive-set-componnt-index / 12,
   /128/               0 / ['decrypted-firmware'] /,
   /129/             / directive-override-parameters / 20, {
   /130/               / parameter-image-digest / 3: << [
   /131/                 / algorithm-id / -16 / SHA256 /,
   /132/                 / digest-bytes /
   /133/                   h'36921488FE6680712F734E11F58D87EE
   /134/                     B66D4B21A8A1AD3441060814DA16D50F'
   /135/               ] >>,
   /136/               / parameter-image-size / 14: 30
   /137/             }
   /138/           ] >>
   /139/         } >>,
   /140/         / manifest-component-id / 5: [
   /141/           'dependency-manifest.suit'
   /142/         ],
   /143/         / validate / 7: << [
   /144/           / condition-image-match / 3, 15
   /145/         ] >>,
   /146/         / install / 20: << [
   /147/           / directive-set-component-index / 12,
   /148/             0 / ['decrypted-firmware'] /,
   /149/           / directive-write / 18, 15
   /150/             / consumes the SUIT_Encryption_Info /
   /151/             / set by the dependent /,
   /152/           / condition-image-match / 3, 15
   /153/             / check the integrity of the decrypted payload /
   /154/         ] >>
   /155/       } >>
   /156/     })
   /157/   >>
   /158/ })

   In hex format, the SUIT manifest is this:



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   D86BA3025873825824822F5820A00CB6C85515C1EF471B50B542FACDD88B
   71B3C7EA2A43DE13D32C4A99056FE9584AD28443A10128A0F65840300030
   1B7C54B3383CC4723C4B7BE667C6760C504213A105DD38401BED5EEF8EB9
   15F8313420104F59467D76790A0EA220B6021B4ED87051B3B4A8D05F7E02
   540359016CA501010201035837A201A101A101815818646570656E64656E
   63792D6D616E69666573742E73756974028181526465637279707465642D
   6669726D77617265058157646570656E64656E742D6D616E69666573742E
   737569741459010F8E0C0014A212582E758C4B7BBAE2C4C1D462423E0F0D
   C3164FFA7B85BB94D4BD6D7ED26AB32FEB063385D4D3465927EC82CB5E19
   8A5913588CD8608443A10101A1054CF14AAB9D81D51F7AD943FE87F68183
   44A101381CA220A40102200121582073024F415AA51529A66CCEFD88F3F6
   2A734492FF45F6AD37FD2888E73EAF19DA2258204005B48A6FD091AA6ABF
   E3CFBEEDE88B347E521D43405FDBD7D2CFF0EBC21B2604456B69642D3258
   18A06B8E6550F308712B1DF044B21B7D11D9B22792F1DE09970C0114A303
   5824822F58204B15C90FBD776A820E7E733DF040D90B356B5C75982ECAEC
   E8673818179BDF160E18F7157423646570656E64656E63792D6D616E6966
   657374150F070F0B0F7423646570656E64656E63792D6D616E6966657374
   58F7D86BA2025873825824822F58204B15C90FBD776A820E7E733DF040D9
   0B356B5C75982ECAECE8673818179BDF16584AD28443A10128A0F65840BF
   95C29295B45470EF819E7F4E3C9084F4534E26469C0A0F2B8B9664881A53
   59D500F81BD3A6436A025C3E92E51CD7148F83DF47D29FF253F8D41B4D35
   0A2B7503587BA601010201035849A2028181526465637279707465642D66
   69726D7761726504582F840C0014A2035824822F582036921488FE668071
   2F734E11F58D87EEB66D4B21A8A1AD3441060814DA16D50F0E181E058158
   18646570656E64656E63792D6D616E69666573742E73756974074382030F
   1447860C00120F030F

10.  Operational Considerations

   The algorithms outlined in this document assume that the party
   responsible for payload encryption:

   *  shares a key-encryption key (KEK) with the recipient (for use with
      the AES Key Wrap scheme), or

   *  possesses the recipient's public key (for use with ES-DH).

   Both scenarios necessitate initial communication to distribute these
   keys among the involved parties.  This interaction can be facilitated
   by a device management protocol, as described in [RFC9019], or may
   occur earlier in the device lifecycle, such as during manufacturing
   or commissioning.  In addition to the keying material, key
   identifiers and algorithm information must also be provisioned.  This
   specification does not impose any requirements on the structure of
   the key identifier.






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   In certain situations, third-party companies analyze binaries for
   known security vulnerabilities.  However, encrypted payloads hinder
   this type of analysis.  Consequently, these third-party companies
   must either be granted access to the plaintext binary before
   encryption or be authorized recipients of the encrypted payloads.

11.  Security Considerations

   This entire document focuses on security.

   It is considered best security practice to use different keys for
   different purposes.  For instance, the key-encryption key (KEK)
   utilized in an AES-KW-based content key distribution method for
   encryption should be distinct from the long-term symmetric key
   employed for authentication in a communication security protocol.

   The recipient MUST verify that the algorithm identifiers carried in
   both the outer header of the COSE_Encrypt structure and within each
   recipient structure correspond to the algorithm configuration
   expected at the recipient, as defined by local policy.  If any
   mismatch is detected between the algorithm identifiers and the
   configured algorithms, the recipient MUST reject the message.  This
   prevents an attacker from modifying the algorithm field to perform a
   downgrade attack (for example, changing an AEAD cipher to a non-AEAD
   cipher) or to cause the recipient to use a key for an unintended
   purpose.

   To further minimize the attack surface, it may be advantageous to use
   different long-term keys for encrypting various types of payloads.
   For example, KEK_1 could be used with an AES-KW content key
   distribution method to encrypt a firmware image, while KEK_2 would
   encrypt configuration data.

   A substantial part of this document focuses on content key
   distribution, utilizing two primary methods: AES Key Wrap (AES-KW)
   and Ephemeral-Static Diffie-Hellman (ES-DH).  The key properties
   associated with their deployment are summarized in Table 3.














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   +=================+=====================+============+==============+
   | Number ofLong-  | Number of           |Use Case    | Recommended? |
   | TermKeys        | ContentEncryption   |            |              |
   |                 | Keys (CEKs)         |            |              |
   +=================+=====================+============+==============+
   | Same key        | Single CEK per      |Legacy Usage| No, bad      |
   | for all         | payload shared      |            | practice     |
   | devices         | with all devies     |            |              |
   +-----------------+---------------------+------------+--------------+
   | One key         | Single CEK per      |Efficient   | Yes          |
   | per device      | payload shared      |Payload     |              |
   |                 | with all devies     |Distribution|              |
   +-----------------+---------------------+------------+--------------+
   | One Key         | One CEK per         |Point-to-   | Yes          |
   | per device      | payload             |Point       |              |
   |                 | encryption          |Payload     |              |
   |                 | transaction         |Distribution|              |
   |                 | per device          |            |              |
   +-----------------+---------------------+------------+--------------+

               Table 3: Content Key Distribution: Comparison

   The use of firmware encryption in battery-powered IoT devices
   introduces the risk of a battery exhaustion attack.  This attack
   exploits the high energy cost of flash memory operations.  To execute
   this attack, the adversary must be able to swap detached payloads and
   trick the device into processing an incorrect payload.  Payload
   swapping is feasible only if there is no communication security
   protocol between the device and the distribution system or if the
   distribution system itself has been compromised.

   While the security features provided by the manifest can detect this
   attack and prevent the device from booting with an incorrectly
   supplied payload, the energy-intensive flash operations will have
   already occurred.  As a result, these operations can diminish the
   lifespan of the devices, making battery-powered IoT devices
   particularly susceptible to such attacks.  For further discussion on
   IoT devices using flash memory, see Section 8.

   Including the digest of the encrypted firmware in the manifest
   enables the device to detect a battery exhaustion attack before
   energy-consuming decryption and flash memory copy or swap operations
   take place.

   As specified in Section 8 of [RFC9459], recipients must perform
   integrity checks before decryption to mitigate padding oracle
   vulnerabilities, particularly when using the AES-CTR mode.  This
   practice not only prevents padding oracle attacks but also protects



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   against format and decryption oracles, as decryption is skipped if
   the integrity check fails.  For further details on payload integrity
   validation, see Section 7.2.

   The same combination of IV and AES key MUST NOT be reused.  This
   requirement applies not only to AES-CTR mode, as specified in
   Section 4 of [RFC9459], but also to other content encryption
   algorithms, including AEAD ciphers like AES-GCM.

   Although the examples in this document use the coaps scheme for
   payload retrieval, alternative URI schemes like coap and http can
   also be used.  This flexibility is possible because the SUIT manifest
   and this extension do not rely on the TLS layer for security.

   Confidentiality, integrity, and authentication are ensured by the
   SUIT manifest and the extensions defined in this document.  For
   details on how the SUIT manifest meets the security requirements
   outlined in [RFC9124], refer to Section 12 of
   [I-D.ietf-suit-manifest].  Additional security considerations for the
   cryptographic primitives used in these extensions are discussed in
   Section 11 of [RFC9053] and Section 8 of [RFC9459].

12.  IANA Considerations

   IANA is asked to add the following value to the SUIT Parameters
   registry at [iana-suit], which is established by Section 11.5 of
   [I-D.ietf-suit-manifest]:

   Label      Name                 Reference
   -----------------------------------------
   TBD19      Encryption Info      Section 4

   RFC Editor's Note (TBD19): The value for the Encryption Info
   parameter is set to 19, as the proposed value.

13.  References

13.1.  Normative References

   [I-D.ietf-suit-manifest]
              Moran, B., Tschofenig, H., Birkholz, H., Zandberg, K., and
              O. Rønningstad, "A Concise Binary Object Representation
              (CBOR)-based Serialization Format for the Software Updates
              for Internet of Things (SUIT) Manifest", Work in Progress,
              Internet-Draft, draft-ietf-suit-manifest-34, 28 May 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-suit-
              manifest-34>.




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   [I-D.ietf-suit-mti]
              Moran, B., Rønningstad, O., and A. Tsukamoto,
              "Cryptographic Algorithms for Internet of Things (IoT)
              Devices", Work in Progress, Internet-Draft, draft-ietf-
              suit-mti-23, 22 July 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-suit-
              mti-23>.

   [I-D.ietf-suit-trust-domains]
              Moran, B. and K. Takayama, "Software Update for the
              Internet of Things (SUIT) Manifest Extensions for Multiple
              Trust Domain", Work in Progress, Internet-Draft, draft-
              ietf-suit-trust-domains-12, 22 July 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-suit-
              trust-domains-12>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC3394]  Schaad, J. and R. Housley, "Advanced Encryption Standard
              (AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394,
              September 2002, <https://www.rfc-editor.org/rfc/rfc3394>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC9052]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Structures and Process", STD 96, RFC 9052,
              DOI 10.17487/RFC9052, August 2022,
              <https://www.rfc-editor.org/rfc/rfc9052>.

   [RFC9053]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
              August 2022, <https://www.rfc-editor.org/rfc/rfc9053>.

   [RFC9459]  Housley, R. and H. Tschofenig, "CBOR Object Signing and
              Encryption (COSE): AES-CTR and AES-CBC", RFC 9459,
              DOI 10.17487/RFC9459, September 2023,
              <https://www.rfc-editor.org/rfc/rfc9459>.

13.2.  Informative References

   [I-D.ietf-teep-usecase-for-cc-in-network]
              Chen, M., Yang, P., Su, L., and T. Pang, "TEEP Usecase for
              Confidential Computing in Network", Work in Progress,



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              Internet-Draft, draft-ietf-teep-usecase-for-cc-in-network-
              11, 30 June 2025, <https://datatracker.ietf.org/doc/html/
              draft-ietf-teep-usecase-for-cc-in-network-11>.

   [iana-suit]
              Internet Assigned Numbers Authority, "IANA SUIT Manifest
              Registry", 2023, <TBD>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/rfc/rfc5280>.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <https://www.rfc-editor.org/rfc/rfc5652>.

   [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
              Key Derivation Function (HKDF)", RFC 5869,
              DOI 10.17487/RFC5869, May 2010,
              <https://www.rfc-editor.org/rfc/rfc5869>.

   [RFC8937]  Cremers, C., Garratt, L., Smyshlyaev, S., Sullivan, N.,
              and C. Wood, "Randomness Improvements for Security
              Protocols", RFC 8937, DOI 10.17487/RFC8937, October 2020,
              <https://www.rfc-editor.org/rfc/rfc8937>.

   [RFC9019]  Moran, B., Tschofenig, H., Brown, D., and M. Meriac, "A
              Firmware Update Architecture for Internet of Things",
              RFC 9019, DOI 10.17487/RFC9019, April 2021,
              <https://www.rfc-editor.org/rfc/rfc9019>.

   [RFC9124]  Moran, B., Tschofenig, H., and H. Birkholz, "A Manifest
              Information Model for Firmware Updates in Internet of
              Things (IoT) Devices", RFC 9124, DOI 10.17487/RFC9124,
              January 2022, <https://www.rfc-editor.org/rfc/rfc9124>.

   [RFC9397]  Pei, M., Tschofenig, H., Thaler, D., and D. Wheeler,
              "Trusted Execution Environment Provisioning (TEEP)
              Architecture", RFC 9397, DOI 10.17487/RFC9397, July 2023,
              <https://www.rfc-editor.org/rfc/rfc9397>.

   [ROP]      Wikipedia, "Return-Oriented Programming", March 2023,
              <https://en.wikipedia.org/wiki/Return-
              oriented_programming>.





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   [SP800-56] NIST, "Recommendation for Pair-Wise Key Establishment
              Schemes Using Discrete Logarithm Cryptography, NIST
              Special Publication 800-56A Revision 3", April 2018,
              <http://nvlpubs.nist.gov/nistpubs/SpecialPublications/
              NIST.SP.800-56Ar3.pdf>.

Appendix A.  Full CDDL

   The following CDDL must be appended to the SUIT Manifest CDDL.  The
   SUIT CDDL is defined in Appendix A of [I-D.ietf-suit-manifest]

   SUIT_Encryption_Info = #6.96(COSE_Encrypt)

   $$SUIT_Parameters //= (suit-parameter-encryption-info =>
       bstr .cbor SUIT_Encryption_Info)

   suit-parameter-encryption-info = 19

Acknowledgements

   We would like to thank Henk Birkholz for his feedback on the CDDL
   description in this document.  Additionally, we would like to thank
   Michael Richardson, Dick Brooks, Øyvind Rønningstad, Dave Thaler,
   Laurence Lundblade, Christian Amsüss, Ruud Derwig, Martin Thomson.
   Kris Kwiatkowski, Suresh Krishnan and Carsten Bormann for their
   review feedback.

   We would like to thank the IESG, in particular Deb Cooley, Éric
   Vyncke and Roman Danyliw, for their help to improve the quality of
   this document.

Authors' Addresses

   Hannes Tschofenig
   University of Applied Sciences Bonn-Rhein-Sieg
   Email: Hannes.Tschofenig@gmx.net


   Russ Housley
   Vigil Security, LLC
   Email: housley@vigilsec.com


   Brendan Moran
   Arm Limited
   Email: Brendan.Moran@arm.com





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   David Brown
   Linaro
   Email: david.brown@linaro.org


   Ken Takayama
   SECOM CO., LTD.
   Email: ken.takayama.ietf@gmail.com











































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name: draft-ietf-tls-deprecate-obsolete-kex
rev: 08
title: Deprecating Obsolete Key Exchange Methods in (D)TLS 1.2
time: 2026-01-23T18:29:16Z
group_uri: /api/v1/group/group/1326/
expires: 2026-07-16T17:28:09Z
ad: /api/v1/person/person/112723/
shepherd: /api/v1/person/email/joe@salowey.net/
categories: ["Policy/governance"]
tags: []
fetched_at: 2026-02-27T22:56:09.014935+00:00
abstract:
For (D)TLS 1.2, this document deprecates the use of two key
   exchanges, namely Diffie-Hellman over a finite field and RSA, and it
   discourages the use of static elliptic curve Diffie-Hellman cipher
   suites.

   These prescriptions apply only to (D)TLS 1.2 since (D)TLS 1.0 and TLS
   1.1 are deprecated by RFC 8996 and (D)TLS 1.3 either does not use the
   affected algorithms or does not share the relevant configuration
   options.  (There is no DTLS version 1.1.)

   This document updates RFCs 9325, 4346, 5246, 4162, 6347, 5932, 5288,
   6209, 6367, 8422, 5289, 5469, 4785, 4279, 5487, 6655, and 7905, to
   deprecate or discourage - i.e., change to MUST NOT or SHOULD NOT, as
   listed in Section 5.3, Section 5.2, Section 5.3, Section 5.4, and
   Section 5.5 - the use of cipher suites using the above key exchange
   methods in (D)TLS 1.2 connections.

states:
["/api/v1/doc/state/1/", "/api/v1/doc/state/108/", "/api/v1/doc/state/115/", "/api/v1/doc/state/17/", "/api/v1/doc/state/117/", "/api/v1/doc/state/44/"]

full_text:
TLS Working Group                                              N. Aviram
Internet-Draft                                           12 January 2026
Updates: 9325, 4346, 5246, 4162, 6347, 5932,                            
         5288, 6209, 6367, 8422, 5289, 5469,                            
         4785, 4279, 5487, 6655, 7905 (if                               
         approved)                                                      
Intended status: Standards Track                                        
Expires: 16 July 2026


        Deprecating Obsolete Key Exchange Methods in (D)TLS 1.2
                draft-ietf-tls-deprecate-obsolete-kex-08

Abstract

   For (D)TLS 1.2, this document deprecates the use of two key
   exchanges, namely Diffie-Hellman over a finite field and RSA, and it
   discourages the use of static elliptic curve Diffie-Hellman cipher
   suites.

   These prescriptions apply only to (D)TLS 1.2 since (D)TLS 1.0 and TLS
   1.1 are deprecated by RFC 8996 and (D)TLS 1.3 either does not use the
   affected algorithms or does not share the relevant configuration
   options.  (There is no DTLS version 1.1.)

   This document updates RFCs 9325, 4346, 5246, 4162, 6347, 5932, 5288,
   6209, 6367, 8422, 5289, 5469, 4785, 4279, 5487, 6655, and 7905, to
   deprecate or discourage - i.e., change to MUST NOT or SHOULD NOT, as
   listed in Section 5.3, Section 5.2, Section 5.3, Section 5.4, and
   Section 5.5 - the use of cipher suites using the above key exchange
   methods in (D)TLS 1.2 connections.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 16 July 2026.



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Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Non-Ephemeral Diffie-Hellman  . . . . . . . . . . . . . . . .   5
   3.  Ephemeral Finite Field Diffie-Hellman . . . . . . . . . . . .   5
   4.  RSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Updates to Cipher Suites and TLS ClientCertificateType
           Identifiers . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  DH Cipher Suites Deprecated by This Document  . . . . . .   5
     5.2.  ECDH Cipher Suites Whose Use Is Discouraged by This
           Document  . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.3.  DHE Cipher Suites deprecated by This Document . . . . . .  10
     5.4.  RSA Cipher Suites Deprecated by This Document . . . . . .  13
     5.5.  TLS ClientCertificateType Identifiers Deprecated by This
           Document  . . . . . . . . . . . . . . . . . . . . . . . .  16
   6.  Updating RFC 9325 . . . . . . . . . . . . . . . . . . . . . .  16
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  18
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     10.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   (D)TLS 1.2 supports a variety of key exchange algorithms, including
   RSA, Diffie-Hellman over a finite field, and elliptic curve Diffie-
   Hellman (ECDH).

   Diffie-Hellman key exchange, over any group, comes in ephemeral and
   non-ephemeral varieties.  Non-ephemeral DH algorithms use static DH
   public keys included in the authenticating peer's certificate; see



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   [RFC4492] for discussion.  In contrast, ephemeral DH algorithms use
   ephemeral DH public keys sent in the handshake and authenticated by
   the peer's certificate.  Ephemeral and non-ephemeral finite field DH
   algorithms are called DHE and DH (or FFDHE and FFDH), respectively,
   and ephemeral and non-ephemeral elliptic curve DH algorithms are
   called ECDHE and ECDH, respectively [RFC4492].

   In general, non-ephemeral cipher suites are not recommended due to
   their lack of forward secrecy.  Moreover, as demonstrated by the
   [Raccoon] attack on finite-field DH, public key reuse, either via
   non-ephemeral cipher suites or reused keys with ephemeral cipher
   suites, can lead to timing side channels that may leak connection
   secrets.  For elliptic curve DH, invalid curve attacks similarly
   exploit secret reuse in order to break security [ICA], further
   demonstrating the risk of reusing public keys.  While both side
   channels can be avoided in implementations, experience shows that in
   practice, implementations may fail to thwart such attacks due to the
   complexity and number of the required mitigations.

   Additionally, RSA key exchange suffers from security problems that
   are independent of implementation choices as well as problems that
   stem purely from the difficulty of implementing security
   countermeasures correctly.

   At a rough glance, the problems affecting FFDHE in (D)TLS 1.2 are as
   follows:

   1.  FFDHE suffers from interoperability problems because there is no
       mechanism for negotiating the group, and some implementations
       only support small group sizes (see [RFC7919], Section 1).

   2.  FFDHE groups may have small subgroups, which enables several
       attacks [subgroups].  When presented with a custom, non-
       standardized FFDHE group, a handshaking client cannot practically
       verify that the group chosen by the server does not suffer from
       this problem.  There is also no mechanism for such handshakes to
       fall back to other key exchange parameters that are acceptable to
       the client.  Custom FFDHE groups are widespread (as a result of
       advice based on [weak-dh]).  Therefore, clients cannot simply
       reject handshakes that present custom, and thus potentially
       dangerous, groups.

   3.  In practice, some operators use 1024-bit FFDHE groups since this
       is the maximum size that ensures wide support (see [RFC7919],
       Section 1).  This size leaves only a small security margin vs.
       the current discrete log record, which stands at 795 bits
       [DLOG795].




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   4.  Expanding on the previous point, just a handful of very large
       computations allow an attacker to cheaply decrypt a relatively
       large fraction of FFDHE traffic (namely, traffic encrypted using
       particular standardized groups) [weak-dh].

   5.  When secrets are not fully ephemeral, FFDHE suffers from the
       [Raccoon] side channel attack.  (Note that FFDH is inherently
       vulnerable to the Raccoon attack unless constant-time mitigations
       are employed.)

   The problems affecting RSA key exchange in (D)TLS 1.2 are as follows:

   1.  RSA key exchange offers no forward secrecy, by construction.

   2.  RSA key exchange may be vulnerable to Bleichenbacher's attack
       [BLEI].  Experience shows that variants of this attack arise
       every few years because implementing the relevant countermeasure
       correctly is difficult (see [ROBOT], [NEW-BLEI], [DROWN]).

   3.  In addition to the above point, there is no convenient mechanism
       in (D)TLS 1.2 for the domain separation of keys.  Therefore, a
       single endpoint that is vulnerable to Bleichenbacher's attack
       would affect all endpoints sharing the same RSA key (see [XPROT],
       [DROWN]).

   This document updates [RFC9325], [RFC4346], [RFC5246], [RFC4162],
   [RFC6347], [RFC5932], [RFC5288], [RFC6209], [RFC6367], [RFC8422],
   [RFC5289], [RFC4785], [RFC4279], [RFC5487], [RFC6655], [RFC7905] and
   [RFC5469] to remediate the above problems, by deprecating and
   discouraging the use of affected cipher suites, as listed in
   Section 5.3 Section 5.2 Section 5.3 Section 5.4 Section 5.5.

   BCP 195 [RFC8996][RFC9325] contains the latest IETF recommendations
   for users of the (D)TLS protocol (and specifically, (D)TLS 1.2) and
   this document supersedes it in several points.  Section 6 details the
   exact differences.  All other recommendations of the BCP document
   remain valid.

1.1.  Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.






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2.  Non-Ephemeral Diffie-Hellman

   Clients MUST NOT offer and servers MUST NOT select non-ephemeral FFDH
   cipher suites in (D)TLS 1.2 connections.  (Note that (D)TLS 1.0 and
   TLS 1.1 are deprecated by [RFC8996] and (D)TLS 1.3 does not support
   FFDH [I-D.ietf-tls-rfc8446bis][RFC9147].)  This includes all cipher
   suites listed in the table in Section 5.1.

   Clients SHOULD NOT offer and servers SHOULD NOT select non-ephemeral
   ECDH cipher suites in (D)TLS 1.2 connections.  (This requirement is
   already present in [RFC9325].  Note that (D)TLS 1.0 and TLS 1.1 are
   deprecated by [RFC8996] and (D)TLS 1.3 does not support ECDH
   [I-D.ietf-tls-rfc8446bis][RFC9147].)  This includes all cipher suites
   listed in the table in Section 5.2.

   In addition, to avoid the use of non-ephemeral Diffie-Hellman,
   clients SHOULD NOT use and servers SHOULD NOT accept certificates
   with fixed DH parameters.  These certificate types are rsa_fixed_dh,
   dss_fixed_dh, rsa_fixed_ecdh and ecdsa_fixed_ecdh as listed in
   Section 5.5.  These values only apply to (D)TLS versions of 1.2 and
   below.

3.  Ephemeral Finite Field Diffie-Hellman

   Clients MUST NOT offer and servers MUST NOT select FFDHE cipher
   suites in (D)TLS 1.2 connections.  This includes all cipher suites
   listed in the table in Section 5.3.  (Note that (D)TLS 1.0 and TLS
   1.1 are deprecated by [RFC8996].)  FFDHE cipher suites in (D)TLS 1.3
   do not suffer from the problems presented in Section 1; see
   [I-D.ietf-tls-rfc8446bis] and [RFC9147].  Therefore, clients and
   servers MAY offer FFDHE cipher suites in (D)TLS 1.3 connections.

4.  RSA

   Clients MUST NOT offer and servers MUST NOT select RSA cipher suites
   in (D)TLS 1.2 connections.  (Note that (D)TLS 1.0 and TLS 1.1 are
   deprecated by [RFC8996], and (D)TLS 1.3 does not support static RSA
   [I-D.ietf-tls-rfc8446bis][RFC9147].)  This includes all cipher suites
   listed in the table in Section 5.4.  Note that these cipher suites
   are already marked as not recommended in the "TLS Cipher Suites"
   registry [tls-registry].

5.  Updates to Cipher Suites and TLS ClientCertificateType Identifiers

5.1.  DH Cipher Suites Deprecated by This Document

   This document requests IANA to set the “recommended” column to “D”
   for the following entries:



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     +==========================================+====================+
     | Ciphersuite                              | Reference          |
     +==========================================+====================+
     | TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA     | [RFC4346]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_DES_CBC_SHA              | [RFC5469]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA         | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA     | [RFC4346]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_DES_CBC_SHA              | [RFC5469]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA         | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_EXPORT_WITH_RC4_40_MD5       | [RFC4346][RFC6347] |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_RC4_128_MD5             | [RFC5246][RFC6347] |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA    | [RFC4346]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_DES_CBC_SHA             | [RFC5469]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_3DES_EDE_CBC_SHA        | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_AES_128_CBC_SHA          | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_AES_128_CBC_SHA          | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_AES_128_CBC_SHA         | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_AES_256_CBC_SHA          | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_AES_256_CBC_SHA          | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_AES_256_CBC_SHA         | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_AES_128_CBC_SHA256       | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_AES_128_CBC_SHA256       | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_CAMELLIA_128_CBC_SHA     | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_CAMELLIA_128_CBC_SHA     | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_CAMELLIA_128_CBC_SHA    | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_AES_256_CBC_SHA256       | [RFC5246]          |



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     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_AES_256_CBC_SHA256       | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_AES_128_CBC_SHA256      | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_AES_256_CBC_SHA256      | [RFC5246]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_CAMELLIA_256_CBC_SHA     | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_CAMELLIA_256_CBC_SHA     | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_CAMELLIA_256_CBC_SHA    | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_SEED_CBC_SHA             | [RFC4162]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_SEED_CBC_SHA             | [RFC4162]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_SEED_CBC_SHA            | [RFC4162]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_AES_128_GCM_SHA256       | [RFC5288]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_AES_256_GCM_SHA384       | [RFC5288]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_AES_128_GCM_SHA256       | [RFC5288]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_AES_256_GCM_SHA384       | [RFC5288]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_AES_128_GCM_SHA256      | [RFC5288]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_AES_256_GCM_SHA384      | [RFC5288]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_CAMELLIA_128_CBC_SHA256  | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_CAMELLIA_128_CBC_SHA256  | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_CAMELLIA_128_CBC_SHA256 | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_CAMELLIA_256_CBC_SHA256  | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_CAMELLIA_256_CBC_SHA256  | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_CAMELLIA_256_CBC_SHA256 | [RFC5932]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_ARIA_128_CBC_SHA256      | [RFC6209]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_ARIA_256_CBC_SHA384      | [RFC6209]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_ARIA_128_CBC_SHA256      | [RFC6209]          |



Aviram                    Expires 16 July 2026                  [Page 7]

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     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_ARIA_256_CBC_SHA384      | [RFC6209]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_ARIA_128_CBC_SHA256     | [RFC6209]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_ARIA_256_CBC_SHA384     | [RFC6209]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_ARIA_128_GCM_SHA256      | [RFC6209]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_ARIA_256_GCM_SHA384      | [RFC6209]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_ARIA_128_GCM_SHA256      | [RFC6209]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_ARIA_256_GCM_SHA384      | [RFC6209]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_ARIA_128_GCM_SHA256     | [RFC6209]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_ARIA_256_GCM_SHA384     | [RFC6209]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_CAMELLIA_128_GCM_SHA256  | [RFC6367]          |
     +------------------------------------------+--------------------+
     | TLS_DH_RSA_WITH_CAMELLIA_256_GCM_SHA384  | [RFC6367]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_CAMELLIA_128_GCM_SHA256  | [RFC6367]          |
     +------------------------------------------+--------------------+
     | TLS_DH_DSS_WITH_CAMELLIA_256_GCM_SHA384  | [RFC6367]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_CAMELLIA_128_GCM_SHA256 | [RFC6367]          |
     +------------------------------------------+--------------------+
     | TLS_DH_anon_WITH_CAMELLIA_256_GCM_SHA384 | [RFC6367]          |
     +------------------------------------------+--------------------+

                                  Table 1

5.2.  ECDH Cipher Suites Whose Use Is Discouraged by This Document

   [RFC9325] already specifies that implementations SHOULD NOT negotiate
   the following cipher suites; accordingly, they appear with
   "Recommended: N" in the IANA TLS Cipher Suites registry
   [tls-registry].  This document updates them to "Recommended: D" to
   align with [I-D.ietf-tls-rfc8447bis].  It also records the rationale
   for discouraging use of these cipher suites, and cites prior analyses
   and attacks that demonstrate the associated risks.








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   +=============================================+====================+
   | Ciphersuite                                 | Reference          |
   +=============================================+====================+
   | TLS_ECDH_ECDSA_WITH_NULL_SHA                | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_RC4_128_SHA             | [RFC8422][RFC6347] |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_3DES_EDE_CBC_SHA        | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA         | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA         | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_NULL_SHA                  | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_RC4_128_SHA               | [RFC8422][RFC6347] |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_3DES_EDE_CBC_SHA          | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_AES_128_CBC_SHA           | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_AES_256_CBC_SHA           | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_anon_WITH_NULL_SHA                 | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_anon_WITH_RC4_128_SHA              | [RFC8422][RFC6347] |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_anon_WITH_3DES_EDE_CBC_SHA         | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_anon_WITH_AES_128_CBC_SHA          | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_anon_WITH_AES_256_CBC_SHA          | [RFC8422]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA256      | [RFC5289]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA384      | [RFC5289]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_AES_128_CBC_SHA256        | [RFC5289]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_AES_256_CBC_SHA384        | [RFC5289]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_AES_128_GCM_SHA256      | [RFC5289]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384      | [RFC5289]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_AES_128_GCM_SHA256        | [RFC5289]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_AES_256_GCM_SHA384        | [RFC5289]          |



Aviram                    Expires 16 July 2026                  [Page 9]

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   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_ARIA_128_CBC_SHA256     | [RFC6209]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_ARIA_256_CBC_SHA384     | [RFC6209]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_ARIA_128_CBC_SHA256       | [RFC6209]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_ARIA_256_CBC_SHA384       | [RFC6209]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_ARIA_128_GCM_SHA256     | [RFC6209]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_ARIA_256_GCM_SHA384     | [RFC6209]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_ARIA_128_GCM_SHA256       | [RFC6209]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_ARIA_256_GCM_SHA384       | [RFC6209]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_CAMELLIA_128_CBC_SHA256 | [RFC6367]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_CAMELLIA_256_CBC_SHA384 | [RFC6367]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_CAMELLIA_128_CBC_SHA256   | [RFC6367]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_CAMELLIA_256_CBC_SHA384   | [RFC6367]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_CAMELLIA_128_GCM_SHA256 | [RFC6367]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_ECDSA_WITH_CAMELLIA_256_GCM_SHA384 | [RFC6367]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_CAMELLIA_128_GCM_SHA256   | [RFC6367]          |
   +---------------------------------------------+--------------------+
   | TLS_ECDH_RSA_WITH_CAMELLIA_256_GCM_SHA384   | [RFC6367]          |
   +---------------------------------------------+--------------------+

                                 Table 2

5.3.  DHE Cipher Suites deprecated by This Document

   This document requests IANA to set the “recommended” column to “D”
   for the following entries:

    +===========================================+=====================+
    | Ciphersuite                               | Reference           |
    +===========================================+=====================+
    | TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA     | [RFC4346]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_DES_CBC_SHA              | [RFC5469] [RFC8996] |
    +-------------------------------------------+---------------------+



Aviram                    Expires 16 July 2026                 [Page 10]

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    | TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA         | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA     | [RFC4346]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_DES_CBC_SHA              | [RFC5469] [RFC8996] |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA         | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_NULL_SHA                 | [RFC4785]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_AES_128_CBC_SHA          | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_AES_128_CBC_SHA          | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_AES_256_CBC_SHA          | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_AES_256_CBC_SHA          | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_AES_128_CBC_SHA256       | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_CAMELLIA_128_CBC_SHA     | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA     | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_AES_128_CBC_SHA256       | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_AES_256_CBC_SHA256       | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_AES_256_CBC_SHA256       | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_CAMELLIA_256_CBC_SHA     | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA     | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_RC4_128_SHA              | [RFC4279][RFC6347]  |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA         | [RFC4279]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_AES_128_CBC_SHA          | [RFC4279]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_AES_256_CBC_SHA          | [RFC4279]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_SEED_CBC_SHA             | [RFC4162]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_SEED_CBC_SHA             | [RFC4162]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_AES_128_GCM_SHA256       | [RFC5288]           |
    +-------------------------------------------+---------------------+



Aviram                    Expires 16 July 2026                 [Page 11]

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    | TLS_DHE_RSA_WITH_AES_256_GCM_SHA384       | [RFC5288]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_AES_128_GCM_SHA256       | [RFC5288]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_AES_256_GCM_SHA384       | [RFC5288]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_AES_128_GCM_SHA256       | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_AES_256_GCM_SHA384       | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_AES_128_CBC_SHA256       | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_AES_256_CBC_SHA384       | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_NULL_SHA256              | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_NULL_SHA384              | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_CAMELLIA_128_CBC_SHA256  | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA256  | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_CAMELLIA_256_CBC_SHA256  | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA256  | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_ARIA_128_CBC_SHA256      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_ARIA_256_CBC_SHA384      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_ARIA_128_CBC_SHA256      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_ARIA_256_CBC_SHA384      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_ARIA_128_GCM_SHA256      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_ARIA_256_GCM_SHA384      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_ARIA_128_GCM_SHA256      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_ARIA_256_GCM_SHA384      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_ARIA_128_CBC_SHA256      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_ARIA_256_CBC_SHA384      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_ARIA_128_GCM_SHA256      | [RFC6209]           |
    +-------------------------------------------+---------------------+



Aviram                    Expires 16 July 2026                 [Page 12]

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    | TLS_DHE_PSK_WITH_ARIA_256_GCM_SHA384      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_CAMELLIA_128_GCM_SHA256  | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_CAMELLIA_256_GCM_SHA384  | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_CAMELLIA_128_GCM_SHA256  | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_DSS_WITH_CAMELLIA_256_GCM_SHA384  | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_CAMELLIA_128_GCM_SHA256  | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_CAMELLIA_256_GCM_SHA384  | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_CAMELLIA_128_CBC_SHA256  | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_CAMELLIA_256_CBC_SHA384  | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_AES_128_CCM              | [RFC6655]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_AES_256_CCM              | [RFC6655]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_AES_128_CCM_8            | [RFC6655]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_AES_256_CCM_8            | [RFC6655]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_AES_128_CCM              | [RFC6655]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_AES_256_CCM              | [RFC6655]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256 | [RFC7905]           |
    +-------------------------------------------+---------------------+
    | TLS_DHE_PSK_WITH_CHACHA20_POLY1305_SHA256 | [RFC7905]           |
    +-------------------------------------------+---------------------+
    | TLS_PSK_DHE_WITH_AES_128_CCM_8            | [RFC6655]           |
    +-------------------------------------------+---------------------+
    | TLS_PSK_DHE_WITH_AES_256_CCM_8            | [RFC6655]           |
    +-------------------------------------------+---------------------+

                                  Table 3

5.4.  RSA Cipher Suites Deprecated by This Document

   This document requests IANA to set the “recommended” column to “D”
   for the following entries:






Aviram                    Expires 16 July 2026                 [Page 13]

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    +===========================================+=====================+
    | Ciphersuite                               | Reference           |
    +===========================================+=====================+
    | TLS_RSA_WITH_NULL_MD5                     | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_NULL_SHA                     | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_EXPORT_WITH_RC4_40_MD5            | [RFC4346][RFC6347]  |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_RC4_128_MD5                  | [RFC5246][RFC6347]  |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_RC4_128_SHA                  | [RFC5246][RFC6347]  |
    +-------------------------------------------+---------------------+
    | TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5        | [RFC4346]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_IDEA_CBC_SHA                 | [RFC5469] [RFC8996] |
    +-------------------------------------------+---------------------+
    | TLS_RSA_EXPORT_WITH_DES40_CBC_SHA         | [RFC4346]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_DES_CBC_SHA                  | [RFC5469] [RFC8996] |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_3DES_EDE_CBC_SHA             | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_NULL_SHA                 | [RFC4785]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_AES_128_CBC_SHA              | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_AES_256_CBC_SHA              | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_NULL_SHA256                  | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_AES_128_CBC_SHA256           | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_AES_256_CBC_SHA256           | [RFC5246]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA         | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA         | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_RC4_128_SHA              | [RFC4279][RFC6347]  |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_3DES_EDE_CBC_SHA         | [RFC4279]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_AES_128_CBC_SHA          | [RFC4279]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_AES_256_CBC_SHA          | [RFC4279]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_SEED_CBC_SHA                 | [RFC4162]           |



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    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_AES_128_GCM_SHA256           | [RFC5288]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_AES_256_GCM_SHA384           | [RFC5288]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_AES_128_GCM_SHA256       | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_AES_256_GCM_SHA384       | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_AES_128_CBC_SHA256       | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_AES_256_CBC_SHA384       | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_NULL_SHA256              | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_NULL_SHA384              | [RFC5487]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA256      | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA256      | [RFC5932]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_ARIA_128_CBC_SHA256          | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_ARIA_256_CBC_SHA384          | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_ARIA_128_GCM_SHA256          | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_ARIA_256_GCM_SHA384          | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_ARIA_128_CBC_SHA256      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_ARIA_256_CBC_SHA384      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_ARIA_128_GCM_SHA256      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_ARIA_256_GCM_SHA384      | [RFC6209]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_CAMELLIA_128_GCM_SHA256      | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_CAMELLIA_256_GCM_SHA384      | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_CAMELLIA_128_GCM_SHA256  | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_CAMELLIA_256_GCM_SHA384  | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_CAMELLIA_128_CBC_SHA256  | [RFC6367]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_CAMELLIA_256_CBC_SHA384  | [RFC6367]           |



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    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_AES_128_CCM                  | [RFC6655]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_AES_256_CCM                  | [RFC6655]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_AES_128_CCM_8                | [RFC6655]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_WITH_AES_256_CCM_8                | [RFC6655]           |
    +-------------------------------------------+---------------------+
    | TLS_RSA_PSK_WITH_CHACHA20_POLY1305_SHA256 | [RFC7905]           |
    +-------------------------------------------+---------------------+

                                  Table 4

5.5.  TLS ClientCertificateType Identifiers Deprecated by This Document

   This document requests IANA to set the “recommended” column to “D”
   for the following entries:

                   +=======================+===========+
                   | Certificate Type      | Reference |
                   +=======================+===========+
                   | rsa_fixed_dh (3)      | [RFC5246] |
                   +-----------------------+-----------+
                   | dss_fixed_dh (4)      | [RFC5246] |
                   +-----------------------+-----------+
                   | rsa_fixed_ecdh (65)   | [RFC8422] |
                   +-----------------------+-----------+
                   | ecdsa_fixed_ecdh (66) | [RFC8422] |
                   +-----------------------+-----------+

                                  Table 5

6.  Updating RFC 9325

   This document updates [RFC9325] with respect to the use of (D)TLS
   1.2, and the table below lists the exact changes.  All changes should
   be made in Section 4.1 of [RFC9325].


   // Note to RFC Editor: please replace XXX below by the current RFC
   // number.









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         +============================+=============+============+
         |                            | RFC 9325    |    RFC XXX |
         +============================+=============+============+
         | Non-ephemeral FFDH         | SHOULD NOT  |   MUST NOT |
         +----------------------------+-------------+------------+
         | Non-ephemeral ECDH         | SHOULD NOT  |  No change |
         +----------------------------+-------------+------------+
         | Fixed DH certificate types | Unspecified | SHOULD NOT |
         +----------------------------+-------------+------------+
         | Ephemeral FFDH             | SHOULD NOT  |   MUST NOT |
         +----------------------------+-------------+------------+
         | Static RSA                 | SHOULD NOT  |   MUST NOT |
         +----------------------------+-------------+------------+

                                  Table 6

7.  IANA Considerations

   This document requests IANA to mark the cipher suites from the "TLS
   Cipher Suites" registry [tls-registry], under “Transport Layer
   Security (TLS) Parameters” registry group, listed in Section 5.1,
   Section 5.2, Section 5.3, Section 5.4, and the certificate types from
   the "TLS ClientCertificateType Identifiers" registry listed in
   Section 5.5 as "D" in the "Recommended" column, see
   [I-D.ietf-tls-rfc8447bis].

   For each registry entry in Section 5.1, Section 5.2, Section 5.3,
   Section 5.4, and Section 5.5, IANA is also requested to update the
   registry entry's Reference column to refer to this document.

8.  Security Considerations

   Non-ephemeral finite field DH cipher suites (TLS_DH_*), as well as
   ephemeral key reuse for finite field DH cipher suites, are prohibited
   due to the [Raccoon] attack.  Both are already considered bad
   practice since they do not provide forward secrecy.  However, Raccoon
   revealed that timing side channels in processing TLS premaster
   secrets may be exploited to reveal the encrypted premaster secret.

   As for non-ephemeral elliptic curve DH cipher suites (TLS_ECDH_*),
   forgoing forward secrecy not only allows retroactive decryption in
   the event of key compromise but may also enable a broad category of
   attacks where the attacker exploits key reuse to repeatedly query a
   cryptographic secret.

   This category includes, but is not necessarily limited to, the
   following examples:




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   1.  Invalid curve attacks, where the attacker exploits key reuse to
       repeatedly query and eventually learn the key itself.  These
       attacks have been shown to be practical against real-world TLS
       implementations [ICA].

   2.  Side channel attacks, where the attacker exploits key reuse and
       an additional side channel to learn a cryptographic secret.  As
       one example of such attacks, refer to [MAY4].

   3.  Fault attacks, where the attacker exploits key reuse and
       incorrect calculations to learn a cryptographic secret.  As one
       example of such attacks, see [PARIS256].

   Such attacks are often implementation-dependent, including the above
   examples.  However, these examples demonstrate that building a system
   that reuses keys and avoids this category of attacks is difficult in
   practice.  In contrast, avoiding key reuse not only prevents
   decryption in the event of key compromise, but also precludes this
   category of attacks altogether.  Therefore, this document discourages
   the reuse of elliptic curve DH public keys.

   As for ephemeral finite field Diffie-Hellman in (D)TLS 1.2 (TLS_DHE_*
   and TLS_PSK_DHE_*), as explained above, clients have no practical way
   to support these cipher suites while ensuring they only negotiate
   security parameters that are acceptable to them.  In (D)TLS 1.2, the
   server chooses the Diffie-Hellman group, and custom groups are
   prevalent.  Therefore, once the client includes these cipher suites
   in its handshake and the server presents a custom group, the client
   cannot complete the handshake while ensuring security.  Verifying the
   group structure is prohibitively expensive for the client.  Using a
   safelist of known-good groups is also impractical, since server
   operators were encouraged to generate their own custom group.
   Further, there is no mechanism for the handshake to fall back to
   other parameters, that are acceptable to both the client and server.

9.  Acknowledgments

   This document includes many important contributions from Carrie
   Bartle, who wrote much of the prose, and presented it several times
   at the IETF TLS WG.

   The document was inspired by discussions on the TLS WG mailing list
   and a suggestion by Filippo Valsorda following the release of the
   [Raccoon] attack.  Thanks to Christopher A.  Wood for writing up the
   initial draft of this document.  Thanks also to Thomas Fossati, Sean
   Turner, Joe Salowey, Yaron Sheffer, Christian Buchgraber, John Preuß
   Mattsson and Manuel Pégourié-Gonnard for comments and suggestions.




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10.  References

10.1.  Normative References

   [I-D.ietf-tls-rfc8446bis]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", Work in Progress, Internet-Draft, draft-
              ietf-tls-rfc8446bis-14, 13 September 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              rfc8446bis-14>.

   [I-D.ietf-tls-rfc8447bis]
              Salowey, J. A. and S. Turner, "IANA Registry Updates for
              TLS and DTLS", Work in Progress, Internet-Draft, draft-
              ietf-tls-rfc8447bis-15, 21 July 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              rfc8447bis-15>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC4162]  Lee, H.J., Yoon, J.H., and J.I. Lee, "Addition of SEED
              Cipher Suites to Transport Layer Security (TLS)",
              RFC 4162, DOI 10.17487/RFC4162, August 2005,
              <https://www.rfc-editor.org/rfc/rfc4162>.

   [RFC4279]  Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
              Ciphersuites for Transport Layer Security (TLS)",
              RFC 4279, DOI 10.17487/RFC4279, December 2005,
              <https://www.rfc-editor.org/rfc/rfc4279>.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346,
              DOI 10.17487/RFC4346, April 2006,
              <https://www.rfc-editor.org/rfc/rfc4346>.

   [RFC4785]  Blumenthal, U. and P. Goel, "Pre-Shared Key (PSK)
              Ciphersuites with NULL Encryption for Transport Layer
              Security (TLS)", RFC 4785, DOI 10.17487/RFC4785, January
              2007, <https://www.rfc-editor.org/rfc/rfc4785>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/rfc/rfc5246>.




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   [RFC5288]  Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
              Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
              DOI 10.17487/RFC5288, August 2008,
              <https://www.rfc-editor.org/rfc/rfc5288>.

   [RFC5289]  Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
              256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
              DOI 10.17487/RFC5289, August 2008,
              <https://www.rfc-editor.org/rfc/rfc5289>.

   [RFC5469]  Eronen, P., Ed., "DES and IDEA Cipher Suites for Transport
              Layer Security (TLS)", RFC 5469, DOI 10.17487/RFC5469,
              February 2009, <https://www.rfc-editor.org/rfc/rfc5469>.

   [RFC5487]  Badra, M., "Pre-Shared Key Cipher Suites for TLS with SHA-
              256/384 and AES Galois Counter Mode", RFC 5487,
              DOI 10.17487/RFC5487, March 2009,
              <https://www.rfc-editor.org/rfc/rfc5487>.

   [RFC5932]  Kato, A., Kanda, M., and S. Kanno, "Camellia Cipher Suites
              for TLS", RFC 5932, DOI 10.17487/RFC5932, June 2010,
              <https://www.rfc-editor.org/rfc/rfc5932>.

   [RFC6209]  Kim, W., Lee, J., Park, J., and D. Kwon, "Addition of the
              ARIA Cipher Suites to Transport Layer Security (TLS)",
              RFC 6209, DOI 10.17487/RFC6209, April 2011,
              <https://www.rfc-editor.org/rfc/rfc6209>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/rfc/rfc6347>.

   [RFC6367]  Kanno, S. and M. Kanda, "Addition of the Camellia Cipher
              Suites to Transport Layer Security (TLS)", RFC 6367,
              DOI 10.17487/RFC6367, September 2011,
              <https://www.rfc-editor.org/rfc/rfc6367>.

   [RFC6655]  McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
              Transport Layer Security (TLS)", RFC 6655,
              DOI 10.17487/RFC6655, July 2012,
              <https://www.rfc-editor.org/rfc/rfc6655>.

   [RFC7905]  Langley, A., Chang, W., Mavrogiannopoulos, N.,
              Strombergson, J., and S. Josefsson, "ChaCha20-Poly1305
              Cipher Suites for Transport Layer Security (TLS)",
              RFC 7905, DOI 10.17487/RFC7905, June 2016,
              <https://www.rfc-editor.org/rfc/rfc7905>.




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   [RFC7919]  Gillmor, D., "Negotiated Finite Field Diffie-Hellman
              Ephemeral Parameters for Transport Layer Security (TLS)",
              RFC 7919, DOI 10.17487/RFC7919, August 2016,
              <https://www.rfc-editor.org/rfc/rfc7919>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC8422]  Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
              Curve Cryptography (ECC) Cipher Suites for Transport Layer
              Security (TLS) Versions 1.2 and Earlier", RFC 8422,
              DOI 10.17487/RFC8422, August 2018,
              <https://www.rfc-editor.org/rfc/rfc8422>.

   [RFC8996]  Moriarty, K. and S. Farrell, "Deprecating TLS 1.0 and TLS
              1.1", BCP 195, RFC 8996, DOI 10.17487/RFC8996, March 2021,
              <https://www.rfc-editor.org/rfc/rfc8996>.

   [RFC9147]  Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
              <https://www.rfc-editor.org/rfc/rfc9147>.

   [RFC9325]  Sheffer, Y., Saint-Andre, P., and T. Fossati,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
              2022, <https://www.rfc-editor.org/rfc/rfc9325>.

10.2.  Informative References

   [BLEI]     Bleichenbacher, D., "Chosen Ciphertext Attacks against
              Protocols Based on RSA Encryption Standard PKCS #1",
              Advances in Cryptology -- CRYPTO'98, LNCS vol. 1462,
              pages: 1-12 , 1998.

   [DLOG795]  Boudot, F., Gaudry, P., Guillevic, A., Heninger, N.,
              Thomé, E., and P. Zimmermann, "Comparing the difficulty of
              factorization and discrete logarithm: a 240-digit
              experiment", 17 August 2020,
              <https://eprint.iacr.org/2020/697>.









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   [DROWN]    Aviram, N., Schinzel, S., Somorovsky, J., Heninger, N.,
              Dankel, M., Steube, J., Valenta, L., Adrian, D.,
              Halderman, J. A., Dukhovni, V., Käsper, E., Cohney, S.,
              Engels, S., Paar, C., and Y. Shavitt, "DROWN: Breaking TLS
              using SSLv2", August 2016,
              <https://drownattack.com/drown-attack-paper.pdf>.

   [ICA]      Jager, T., Schwenk, J., and J. Somorovsky, "Practical
              invalid curve attacks on TLS-ECDH", 21 September 2015,
              <https://citeseerx.ist.psu.edu/viewdoc/
              download?doi=10.1.1.704.7932&rep=rep1&type=pdf>.

   [MAY4]     Genkin, D., Valenta, L., and Y. Yarom, "May the fourth be
              with you: A microarchitectural side channel attack on
              several real-world applications of curve25519", n.d.,
              <https://dl.acm.org/doi/pdf/10.1145/3133956.3134029>.

   [NEW-BLEI] Meyer, C., Somorovsky, J., Weiss, E., Schwenk, J.,
              Schinzel, S., and E. Tews, "Revisiting SSL/TLS
              Implementations: New Bleichenbacher Side Channels and
              Attacks", August 2014,
              <https://www.usenix.org/system/files/conference/
              usenixsecurity14/sec14-paper-meyer.pdf>.

   [PARIS256] Devlin, S. and F. Valsorda, "The PARIS256 Attack", n.d.,
              <https://i.blackhat.com/us-18/Wed-August-8/us-18-Valsorda-
              Squeezing-A-Key-Through-A-Carry-Bit-wp.pdf>.

   [Raccoon]  Merget, R., Brinkmann, M., Aviram, N., Somorovsky, J.,
              Mittmann, J., and J. Schwenk, "Raccoon Attack: Finding and
              Exploiting Most-Significant-Bit-Oracles in TLS-DH(E)", 9
              September 2020,
              <https://raccoon-attack.com/RacoonAttack.pdf>.

   [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
              Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
              for Transport Layer Security (TLS)", RFC 4492,
              DOI 10.17487/RFC4492, May 2006,
              <https://www.rfc-editor.org/rfc/rfc4492>.

   [ROBOT]    Boeck, H., Somorovsky, J., and C. Young, "Return Of
              Bleichenbacher's Oracle Threat (ROBOT)", 27th USENIX
              Security Symposium , 2018.








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   [subgroups]
              Valenta, L., Adrian, D., Sanso, A., Cohney, S., Fried, J.,
              Hastings, M., Halderman, J. A., and N. Heninger,
              "Measuring small subgroup attacks against Diffie-Hellman",
              15 October 2016,
              <https://eprint.iacr.org/2016/995/20161017:193515>.

   [tls-registry]
              "Transport Layer Security (TLS) Parameters", n.d.,
              <https://www.iana.org/assignments/tls-parameters/tls-
              parameters.xhtml>.

   [weak-dh]  Adrian, D., Bhargavan, K., Durumeric, Z., Gaudry, P.,
              Green, M., Halderman, J. A., Heninger, N., Springall, D.,
              Thomé, E., Valenta, L., VanderSloot, B., Wustrow, E.,
              Zanella-Béguelin, S., and P. Zimmermann, "Weak Diffie-
              Hellman and the Logjam Attack", October 2015,
              <https://weakdh.org/>.

   [XPROT]    Jager, T., Schwenk, J., and J. Somorovsky, "On the
              Security of TLS 1.3 and QUIC Against Weaknesses in PKCS#1
              v1.5 Encryption", Proceedings of the 22nd ACM SIGSAC
              Conference on Computer and Communications Security , 2015.

Author's Address

   Nimrod Aviram
   Email: nimrod.aviram@gmail.com























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name: draft-ietf-emu-hybrid-pqc-eapaka
rev: 01
title: Enhancing Security in EAP-AKA' with Hybrid Post-Quantum Cryptography
time: 2026-02-26T10:21:30Z
group_uri: /api/v1/group/group/1674/
expires: 2026-08-30T10:21:30Z
states: ["/api/v1/doc/state/1/", "/api/v1/doc/state/150/", "/api/v1/doc/state/38/"]
categories: ["Agent identity/auth"]
tags: []
fetched_at: 2026-02-27T22:56:09.014947+00:00
abstract:
Forward Secrecy for the Extensible Authentication Protocol Method for
   Authentication and Key Agreement (EAP-AKA' FS) is specified in
   [RFC9678], providing updates to [RFC9048] with an optional extension
   that offers ephemeral key exchange using the traditional Ephemeral
   Elliptic Curve Diffie-Hellman (ECDHE) key agreement algorithm for
   achieving perfect forward secrecy (PFS).  However, it is susceptible
   to future threats from Cryptographically Relevant Quantum Computers,
   which could potentially compromise a traditional ephemeral public
   key.  If the adversary has also obtained knowledge of the long-term
   key and ephemeral public key, it could compromise session keys
   generated as part of the authentication run in EAP-AKA'.

   This draft aims to enhance the security of EAP-AKA' FS protocol by
   leveraging PQ/T Hybrid [I-D.ietf-pquip-pqt-hybrid-terminology]
   algorithms to make it quantum-safe.

full_text:
EMU                                                          A. Banerjee
Internet-Draft                                                  T. Reddy
Intended status: Standards Track                                   Nokia
Expires: 30 August 2026                                 26 February 2026


  Enhancing Security in EAP-AKA' with Hybrid Post-Quantum Cryptography
                  draft-ietf-emu-hybrid-pqc-eapaka-01

Abstract

   Forward Secrecy for the Extensible Authentication Protocol Method for
   Authentication and Key Agreement (EAP-AKA' FS) is specified in
   [RFC9678], providing updates to [RFC9048] with an optional extension
   that offers ephemeral key exchange using the traditional Ephemeral
   Elliptic Curve Diffie-Hellman (ECDHE) key agreement algorithm for
   achieving perfect forward secrecy (PFS).  However, it is susceptible
   to future threats from Cryptographically Relevant Quantum Computers,
   which could potentially compromise a traditional ephemeral public
   key.  If the adversary has also obtained knowledge of the long-term
   key and ephemeral public key, it could compromise session keys
   generated as part of the authentication run in EAP-AKA'.

   This draft aims to enhance the security of EAP-AKA' FS protocol by
   leveraging PQ/T Hybrid [I-D.ietf-pquip-pqt-hybrid-terminology]
   algorithms to make it quantum-safe.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-emu-hybrid-pqc-eapaka/.

   Discussion of this document takes place on the emu Working Group
   mailing list (mailto:emu@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/emu/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/emu/.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.



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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 30 August 2026.

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   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Background on EAP-AKA' with perfect forward secrecy . . . . .   4
   5.  Hybrid Enhancements by Design . . . . . . . . . . . . . . . .   5
   6.  Message Fragmentation and Reassembly  . . . . . . . . . . . .   5
   7.  Protocol Construction . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Protocol Call Flow  . . . . . . . . . . . . . . . . . . .   6
     7.2.  Key Steps in protocol construction  . . . . . . . . . . .   8
   8.  Extensions to EAP-AKA' FS . . . . . . . . . . . . . . . . . .   9
     8.1.  AT_PUB_HYBRID . . . . . . . . . . . . . . . . . . . . . .   9
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     11.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13










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1.  Introduction

   Forward Secrecy for the Extensible Authentication Protocol Method for
   Authentication and Key Agreement (EAP-AKA' FS) defined in [RFC9678]
   updates the improved Extensible Authentication Protocol Method for
   3GPP Mobile Network Authentication and Key Agreement (EAP-AKA')
   specified in [RFC9048], with an optional extension providing
   ephemeral key exchange.  This prevents an attacker who has gained
   access to the long term key from obtaining session keys established
   in the past, assuming these have been properly deleted.  EAP-AKA' FS
   mitigates passive attacks (e.g., large scale pervasive monitoring)
   against future sessions.

   Nevertheless, EAP-AKA' FS uses traditional algorithms public-key
   algorithms (e.g., ECDH) which will be broken by a Cryptographically
   Relevant Quantum Computer (CRQC) using Shor's algorithm.  The
   presence of a CRQC would render state-of-the-art, traditional public-
   key algorithms deployed today obsolete and insecure, since the
   assumptions about the intractability of the mathematical problems for
   these algorithms that offer confident levels of security today no
   longer apply in the presence of a CRQC.  A CRQC could recover the
   SHARED_SECRET from the ECDHE public keys (Section 6.3 of [RFC9678]).
   If the adversary has also obtained knowledge of the long-term key, it
   could then compute CK', IK', and the SHARED_SECRET, and any derived
   output keys.  This means that the CRQC would disable the forward
   security capability provided by [RFC9678].

   The migration to PQC is unique in the history of modern digital
   cryptography in that neither the traditional algorithms nor the post-
   quantum algorithms are fully trusted to protect data for the required
   data lifetimes.  The post-quantum algorithms face uncertainty about
   the underlying mathematics, compliance issues, unknown
   vulnerabilities, hardware and software implementations that have not
   had sufficient maturing time to rule out classical cryptanalytic
   attacks and implementation bugs.  During the transition from
   traditional to post-quantum algorithms, there is a desire or a
   requirement for protocols that use both algorithm types.

   This specification defines HPKE [I-D.ietf-hpke-pq]
   [I-D.irtf-cfrg-hybrid-kems] for use with EAP-AKA' FS.  HPKE offers a
   variant of public-key encryption of arbitrary-sized plaintexts for a
   recipient public key.  HPKE works for any combination of an
   asymmetric key encapsulation mechanism (KEM), key derivation function
   (KDF), and authenticated encryption with additional data (AEAD)
   function.  HPKE can be extended to support hybrid post-quantum Key
   Encapsulation Mechanisms (KEMs) as defined in [I-D.ietf-hpke-pq].





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2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Terminology

   This document makes use of the terms defined in
   [I-D.ietf-pquip-pqt-hybrid-terminology].  For the purposes of this
   document, it is helpful to be able to divide cryptographic algorithms
   into two classes:

   "Traditional Algorithm": An asymmetric cryptographic algorithm based
   on integer factorisation, finite field discrete logarithms or
   elliptic curve discrete logarithms.  In the context of JOSE, examples
   of traditional key exchange algorithms include Elliptic Curve Diffie-
   Hellman Ephemeral Static [RFC6090] [RFC8037].  In the context of
   COSE, examples of traditional key exchange algorithms include
   Ephemeral-Static (ES) DH and Static-Static (SS) DH [RFC9052].

   "Post-Quantum Algorithm": An asymmetric cryptographic algorithm that
   is believed to be secure against attacks using quantum computers as
   well as classical computers.  Examples of PQC key exchange algorithms
   include Kyber.

   "Hybrid" key exchange, in this context, means the use of two key
   exchange algorithms based on different cryptographic assumptions,
   e.g., one traditional algorithm and one Post-Quantum algorithm, with
   the purpose of the final shared secret key being secure as long as at
   least one of the component key exchange algorithms remains unbroken.
   It is referred to as PQ/T Hybrid Scheme in
   [I-D.ietf-pquip-pqt-hybrid-terminology].

   PQ/T Hybrid Key Encapsulation Mechanism: A Key Encapsulation
   mechanism (KEM) made up of two or more component KEM algorithms where
   at least one is a post-quantum algorithm and at least one is a
   traditional algorithm.

4.  Background on EAP-AKA' with perfect forward secrecy

   In EAP-AKA', The authentication vector (AV) contains a random part
   RAND, an authenticator part AUTN used for authenticating the network
   to the USIM, an expected result part XRES, a 128-bit session key for
   integrity check IK, and a 128-bit session key for encryption CK.




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   As described in the draft [RFC9678], the server has the EAP identity
   of the peer.  The server asks the AD to run AKA algorithm to generate
   RAND, AUTN, XRES, CK and IK.  Further it also derives CK’ and IK’
   keys which are tied to a particular network name.  The server now
   generates the ephemeral key pair and sends the public key of that key
   pair and the first EAP method message to the peer.  In this EAP
   message, AT_PUB_ECDHE (carries public key) and the AT_KDF_FS(carries
   other FS related parameters).  Both of these might be ignored of USIM
   doesn’t support the Forward Secrecy extension.  The peer checks if it
   wants to have a Forward extension in EAP AKA'.  If yes, then it will
   eventually respond with AT_PUB_ECDHE and MAC.  If not, it will ignore
   AT_PUB_ECDHE.  If the peer wants to participate in FS extension, it
   will then generate its ECDH key pair, calculate a shared key based on
   its private key and server public key.  The server will receive the
   RES from peer and AT_PUB_ECDHE.  The shared key will be generated
   both in the peer and the server with key pairs exchanged, and later
   master key is also generated.

   MK_ECDHE = PRF'(IK'| CK'|SHARED_SECRET,"EAP-AKA' FS"|Identity)

5.  Hybrid Enhancements by Design

   We suggest the following changes and enhancements:

   *  A new attribute, AT_PUB_HYBRID, is defined to carry the public
      key, which is the concatenation of traditional and PQC KEM public
      keys from the EAP server.  The AT_PUB_HYBRID attribute will carry
      the encapsulated key, which is formed by concatenating the
      encapsulated key (enc) from the traditional KEM algorithm and the
      ciphertext (ct) from the PQC KEM Encapsulation function from the
      EAP peer.

   *  The AT_KDF_FS attribute is updated to indicate the PQ/T Hybrid KEM
      in HPKE and HKDF for generating the Hybrid Master Key MK_HYBRID.

   *  Multiple AT_KDF_FS attributes is included in the EAP-Request to
      handle the EAP peer not supporting PQ/T Hybrid KEM in HPKE.

   *  The Hybrid key derivation function will be included first in the
      EAP-Request to indicate a higher priority than the traditional key
      derivation function.

6.  Message Fragmentation and Reassembly

   The message fragmentation and reassembly will be similar to as
   outlined in [I-D.ietf-emu-pqc-eapaka].  For brevity, the authors
   would like to defer the reader to [I-D.ietf-emu-pqc-eapaka] for
   details.



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7.  Protocol Construction

   This section defines the construction for hybrid key exchange in EAP-
   AKA' FS.  Hybrid key exchange refers to using multiple key exchange
   algorithms simultaneously and combining the result with the goal of
   providing security even if all but one of the component algorithms is
   broken.  It is motivated by transition to post-quantum cryptography.

7.1.  Protocol Call Flow

    USIM           Peer                        Server              AD
     |              |                            |                |
     |              |           EAP-Req/Identity |                |
     |              |<---------------------------+                |
     |              |                            |                |
     |              | EAP-Resp/Identity          |                |
     |              | (Privacy-Friendly)         |                |
     |              +--------------------------->|                |
     |      +-------+----------------------------+----------------+--+
     |      | Server now has an identity for the peer. The server    |
     |      | then asks the help of AD to run AKA algorithms,        |
     |      | generating RAND, AUTN, XRES, CK, IK. Typically, the    |
     |      | AD performs the first part of key derivations so that  |
     |      | the authentication server gets the CK' and IK' keys    |
     |      | already tied to a particular network name.             |
     |      +-------+----------------------------+----------------+--+
     |              |                            |                |
     |              |                            | ID, key deriv. |
     |              |                            | function,      |
     |              |                            | network name   |
     |              |                            +--------------->|
     |              |                            |                |
     |              |                            |    RAND, AUTN, |
     |              |                            | XRES, CK', IK' |
     |              |                            |<---------------+
     |      +-------+----------------------------+----------------+--+
     |      | Server now has the needed authentication vector. It    |
     |      | generates a PQC KEM key pair, an ephemeral ECDHE key   |
     |      | pair, sends the hybrid (PQC + ECDHE) public key of that|
     |      | key pair and the first EAP method message to the peer  |
     |      | In the message the AT_PUB_HYBRID attribute             |
     |      | carries the concatenation of PQC KEM and ECDHE public  |
     |      | keys and the AT_KDF_FS attribute carries other         |
     |      | FS-related parameters. Both of these are               |
     |      | skippable attributes that can be ignored if the peer   |
     |      | does not support this extension.                       |
     |      +-------+----------------------------+----------------+--+
     |              |                            |                |



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     |              | EAP-Req/AKA'-Challenge (1),|                |
     |              |  EAP-Req/AKA'-Challenge (2)|                |
     |              |  AT_RAND, AT_AUTN, AT_KDF, |                |
     |              |   AT_KDF_FS, AT_KDF_INPUT, |                |
     |              |       AT_PUB_HYBRID, AT_MAC|                |
     |              |<---------------------------+                |
   +--+--------------+----------------------------+---------+     |
   | The peer checks if it wants to do the FS extension. If |     |
   | yes, it will eventually respond with AT_PUB_HYBRID and |     |
   | AT_MAC. If not, it will ignore AT_PUB_HYBRID and       |     |
   | AT_KDF_FS and base all calculations on basic EAP-AKA'  |     |
   | attributes, continuing just as in EAP-AKA' per RFC     |     |
   | 9048 rules. In any case, the peer needs to query the   |     |
   | auth parameters from the USIM card.                    |     |
   +--+--------------+----------------------------+---------+     |
     |              |                            |                |
     |   RAND, AUTN |                            |                |
     |<-------------+                            |                |
     |              |                            |                |
     | CK, IK, RES  |                            |                |
     +------------->|                            |                |
   +--+--------------+----------------------------+---------+     |
   | The peer now has everything to respond. If it wants to |     |
   | participate in the FS extension, it will then generate |     |
   | its ECDHE key pair, calculate a hybrid shared secret   |     |
   | key based on the server's PQC KEM public key, its ECDHE|     |
   | key pair and the server's ECDHE public key. Finally,   |     |
   | it proceeds to derive all EAP-AKA' key values and      |     |
   | constructs a full response.                            |     |
   +--+--------------+----------------------------+---------+     |
     |              |                            |                |
     |              | EAP-Resp/AKA'-Challenge    |                |
     |              |  EAP-Req/AKA'-Challenge (2)|                |
     |              | AT_RES, AT_PUB_HYBRID,     |                |
     |              | AT_MAC                     |                |
     |              +--------------------------->|                |
     |      +-------+----------------------------+----------------+--+
     |      | The server now has all the necessary values. It        |
     |      | generates the Hybrid shared secret and checks the RES  |
     |      | and MAC values received in AT_RES and AT_MAC,          |
     |      | respectively. Success requires both to be found        |
     |      | correct. Note that when this document is used,         |
     |      | the keys generated from EAP-AKA' are based on CK, IK,  |
     |      | and the ECDHE and PQC KEM values. Even if there was an |
     |      | attacker who held the long-term key, only an active    |
     |      | attacker could have determined the generated session   |
     |      | keys; additionally an attacker with a cryptographically|
     |      | relevant quantum computer cannot get access to the     |



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     |      | server KEM private key and decrypt the data.           |
     |      +-------+----------------------------+----------------+--+
     |              |                            |                |
     |              |                EAP-Success |                |
     |              |<---------------------------+                |
     |              |                            |                |

7.2.  Key Steps in protocol construction

   We outline the following key steps in the protocol:

   *  Server generates the PQC KEM Public key(pq_PK), private key
      (pq_SK) pair and the ECDH public key (trad_PK), private key
      (trad_SK) pair.  The server will generate and send the EAP AKA'
      Authentication Vector (AV).

   *  The server will store the expected response XRES, the ECDH private
      key trad_SK and the PQC KEM private key pq_SK.  The server will
      forward the EAP AKA' AV to peer along with pq_PK and trad_PK.

   *  The USIM will validate the AUTH received, also verifies the MAC.
      After the verification is successful and if the peer also supports
      the Forward secrecy, peer will invoke Encapsulate using
      concat(pq_PK, trad_PK) as defined in section 5.4 of
      [I-D.irtf-cfrg-hybrid-kems].

   "ct" is the concatenation of the ciphertext from PQC KEM and
   encapsulated key from ECDH whereas "ss" is hybrid shared secret key.
   Hybrid shared key ss is generated by the peer using the Encapsulate()
   ([I-D.irtf-cfrg-hybrid-kems]).

   *  The peer will send the Authentication response RES and ct to the
      server.

   *  The server will verify the RES with XRES.  The server will use the
      ct, PQC KEM private key pq_SK and ECDH private key trad_SK to
      generate shared secret.

   The generated ss from Decapsulate is the hybrid shared secret key
   derived from PQC KEM and traditional ECDH.  The peer and the server
   first generate the MK_HYBRID and subsequently generate MSK, EMSK as
   shown below:









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   MK = PRF'(IK'|CK',"EAP-AKA'"|Identity)
   HYBRID_SHARED_SECRET, ct = Encapsulate(pKR)
   MK_HYBRID = PRF'(IK'|CK'| HYBRID_SHARED_SECRET,"EAP-AKA' FS"| Identity)
   K_encr = MK[0..127]
   K_aut = MK[128..383]
   K_re = MK_HYBRID [0..255]
   MSK = MK_HYBRID [256..767]
   EMSK = MK_HYBRID [768..1279]

   where, pkR is concatenation of PQC KEM and traditional public keys of
   the receiver, ct is concatenation of the ciphertext from the PQC KEM
   and encapsulated key from ECDH; the Encapsulate() function is
   perfomed by the peer only.

8.  Extensions to EAP-AKA' FS

8.1.  AT_PUB_HYBRID

   The format of the AT_PUB_HYBRID attribute is shown below.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | AT_PUB_HYBRID    |   Reserved    |      Length (in bytes)     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                       Value (variable)                        |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields are as follows:

   AT_PUB_HYBID:

   This is set to TBA1 BY IANA.

   Reserved:

   A 1-byte field reserved for future use.  Including this field ensures
   that the fixed header (Type, Reserved, Length) is 4 bytes long,
   maintaining 4-byte alignment for the following Value field.  The
   Reserved field MUST be set to 0 on transmission and ignored on
   receipt.

   Length:






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   A 2-byte unsigned integer indicating the total length of the
   attribute in bytes, including the Type, Reserved, Length, and Value
   fields, as well as any padding.  The length is expressed in multiples
   of 4 bytes.

   This differs from the attribute format used in EAP-AKA [RFC4187],
   where the Length field is 1 byte.  The modification is necessary
   because PQ/T Hybrid KEM public keys, such as X25519 and ML-KEM-768
   (e.g., X-Wing), would exceed the 1024-byte limit imposed by the
   original EAP-AKA format.

   Value:

  *  EAP-Request: It contains the public key, which is the concatenation of
     traditional and PQC KEM public keys from the EAP server.
  *  EAP-Response: It contains the encapsulated key, which is formed by
     concatenating the ciphertext (ct) from the PQC KEM Encapsulation function
     and the encapsulated key (enc) from the traditional KEM algorithm and from the
     EAP peer.

   Because the length of the attribute must be a multiple of 4 bytes,
   the sender pads the Value field with zero bytes when necessary.  To
   retain the security of the keys, the sender SHALL generate a fresh
   value for each run of the protocol.

9.  Security Considerations

   ML-KEM is IND-CCA2 secure based on multiple analyses.  The ML-KEM
   variant and its underlying components should be selected consistently
   with the desired security level.  For further clarity on the sizes
   and security levels of ML-KEM variants, please refer to the tables in
   Sections 12 and 13 of [I-D.ietf-pquip-pqc-engineers].

   The security of the ML-KEM algorithm depends on a high-quality
   pseudo-random number generator.  For further discussion on random
   number generation, see [RFC4086].

   In general, good cryptographic practice dictates that a given ML-KEM
   key pair should be used in only one EAP session.  This practice
   mitigates the risk that compromising one EAP session will not
   compromise the security of another EAP session and is essential for
   maintaining forward security.

   For security properties of traditional ECDHE for EAP-AKA FS, see
   section 7 of [RFC9678].  The overall Hybrid scheme needs to be IND-
   CCA2 robust; i.e., atleast one of the schemes should be IND-CCA2
   secure.




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10.  IANA Considerations

   Two new values (TBA2) and (TBA3) in the skippable range need to be
   assigned by IANA for AT_PUB_HYBRID (Section 8.1) in the "Attribute
   Types" registry under the "EAP-AKA and EAP-SIM Parameters" group.

   IANA is requested to update the registry "EAP-AKA' AT_KDF_FS Key
   Derivation Function Values" with the Hybrid key derivation function
   entry:

   +=========+========================================================+=====================================+
   | Value   | Description                                                        | Reference               |
   +=========+========================================================+=====================================+
   | TBA2    | QSF-KEM(ML-KEM-768,P-256)-XOF(SHAKE256)-KDF(SHA3-256)              | [TBD BY IANA: THIS RFC] |
   +=========+===============================+========================+=====================================+
   | TBA3    | KitchenSink-KEM(ML-KEM-768,X25519)-XOF(SHAKE256)-KDF(HKDF-SHA-256) | [TBD BY IANA: THIS RFC] |
   +=========+===============================+========================+=====================================+

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC4187]  Arkko, J. and H. Haverinen, "Extensible Authentication
              Protocol Method for 3rd Generation Authentication and Key
              Agreement (EAP-AKA)", RFC 4187, DOI 10.17487/RFC4187,
              January 2006, <https://www.rfc-editor.org/rfc/rfc4187>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC9048]  Arkko, J., Lehtovirta, V., Torvinen, V., and P. Eronen,
              "Improved Extensible Authentication Protocol Method for
              3GPP Mobile Network Authentication and Key Agreement (EAP-
              AKA')", RFC 9048, DOI 10.17487/RFC9048, October 2021,
              <https://www.rfc-editor.org/rfc/rfc9048>.

   [RFC9180]  Barnes, R., Bhargavan, K., Lipp, B., and C. Wood, "Hybrid
              Public Key Encryption", RFC 9180, DOI 10.17487/RFC9180,
              February 2022, <https://www.rfc-editor.org/rfc/rfc9180>.






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   [RFC9678]  Arkko, J., Norrman, K., and J. Preuß Mattsson, "Forward
              Secrecy Extension to the Improved Extensible
              Authentication Protocol Method for Authentication and Key
              Agreement (EAP-AKA' FS)", RFC 9678, DOI 10.17487/RFC9678,
              March 2025, <https://www.rfc-editor.org/rfc/rfc9678>.

11.2.  Informative References

   [FIPS203]  "FIPS-203: Module-Lattice-based Key-Encapsulation
              Mechanism Standard",
              <https://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.203.pdf>.

   [I-D.ietf-emu-pqc-eapaka]
              Reddy.K, T. and A. Banerjee, "Post-Quantum Key
              Encapsulation Mechanisms (PQ KEMs) in EAP-AKA prime", Work
              in Progress, Internet-Draft, draft-ietf-emu-pqc-eapaka-01,
              26 February 2026, <https://datatracker.ietf.org/doc/html/
              draft-ietf-emu-pqc-eapaka-01>.

   [I-D.ietf-hpke-pq]
              Barnes, R. and D. Connolly, "Post-Quantum and Post-
              Quantum/Traditional Hybrid Algorithms for HPKE", Work in
              Progress, Internet-Draft, draft-ietf-hpke-pq-03, 6
              November 2025, <https://datatracker.ietf.org/doc/html/
              draft-ietf-hpke-pq-03>.

   [I-D.ietf-pquip-pqc-engineers]
              Banerjee, A., Reddy.K, T., Schoinianakis, D., Hollebeek,
              T., and M. Ounsworth, "Post-Quantum Cryptography for
              Engineers", Work in Progress, Internet-Draft, draft-ietf-
              pquip-pqc-engineers-14, 25 August 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-pquip-
              pqc-engineers-14>.

   [I-D.ietf-pquip-pqt-hybrid-terminology]
              D, F., P, M., and B. Hale, "Terminology for Post-Quantum
              Traditional Hybrid Schemes", Work in Progress, Internet-
              Draft, draft-ietf-pquip-pqt-hybrid-terminology-06, 10
              January 2025, <https://datatracker.ietf.org/doc/html/
              draft-ietf-pquip-pqt-hybrid-terminology-06>.

   [I-D.irtf-cfrg-hybrid-kems]
              Connolly, D., Barnes, R., and P. Grubbs, "Hybrid PQ/T Key
              Encapsulation Mechanisms", Work in Progress, Internet-
              Draft, draft-irtf-cfrg-hybrid-kems-08, 27 January 2026,
              <https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-
              hybrid-kems-08>.



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   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,
              <https://www.rfc-editor.org/rfc/rfc4086>.

   [RFC6090]  McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
              Curve Cryptography Algorithms", RFC 6090,
              DOI 10.17487/RFC6090, February 2011,
              <https://www.rfc-editor.org/rfc/rfc6090>.

   [RFC8037]  Liusvaara, I., "CFRG Elliptic Curve Diffie-Hellman (ECDH)
              and Signatures in JSON Object Signing and Encryption
              (JOSE)", RFC 8037, DOI 10.17487/RFC8037, January 2017,
              <https://www.rfc-editor.org/rfc/rfc8037>.

   [RFC9052]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Structures and Process", STD 96, RFC 9052,
              DOI 10.17487/RFC9052, August 2022,
              <https://www.rfc-editor.org/rfc/rfc9052>.

Appendix A.  Acknowledgements

   This draft leverages text from [RFC9678].

Authors' Addresses

   Aritra Banerjee
   Nokia
   London
   United Kingdom
   Email: aritra.banerjee@nokia.com


   Tirumaleswar Reddy
   Nokia
   Bangalore
   Karnataka
   India
   Email: kondtir@gmail.com












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