Signature Authentication in the Internet Key Exchange Version 2 (IKEv2) using PQC
draft-ietf-ipsecme-ikev2-pqc-auth-11

ipsecme                                                         T. Reddy
Internet-Draft                                                     Nokia
Intended status: Standards Track                              V. Smyslov
Expires: 6 February 2027                                      ELVIS-PLUS
                                                              S. Fluhrer
                                                           Cisco Systems
                                                           5 August 2026

Signature Authentication in the Internet Key Exchange Version 2 (IKEv2)
                               using PQC
                  draft-ietf-ipsecme-ikev2-pqc-auth-11

Abstract

   Signature-based authentication methods are utilized in the Internet
   Key Exchange Version 2 (IKEv2).  The current version of the IKEv2
   protocol, specified in RFC 7296, supports traditional digital
   signatures.

   This document specifies a generic mechanism for integrating post-
   quantum cryptographic (PQC) digital signature algorithms into the
   IKEv2 protocol.  The approach allows for seamless inclusion of any
   PQC signature scheme within the existing authentication framework of
   IKEv2.  Additionally, it outlines how Module-Lattice-Based Digital
   Signatures (ML-DSA) and Stateless Hash-Based Digital Signatures (SLH-
   DSA), can be employed as authentication methods within the IKEv2
   protocol, as they have been standardized by US NIST.

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-ipsecme-ikev2-pqc/.

   Discussion of this document takes place on the ipsecme Working Group
   mailing list (mailto:ipsecme@ietf.org), which is archived at
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   https://www.ietf.org/mailman/listinfo/ipsecme/.

Status of This Memo

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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
   3.  General Framework for PQC Authentication in IKEv2 . . . . . .   4
     3.1.  Specifying PQC Signature Algorithms . . . . . . . . . . .   4
     3.2.  Signature Generation and Verification . . . . . . . . . .   5
       3.2.1.  Handling PQC Signatures in IKEv2  . . . . . . . . . .   6
     3.3.  Mechanisms for Signaling Supported Key Pair Types . . . .   7
   4.  Specifying ML-DSA within IKEv2  . . . . . . . . . . . . . . .   8
   5.  Specifying SLH-DSA within IKEv2 . . . . . . . . . . . . . . .   8
   6.  Use of ML-DSA and SLH-DSA . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   References  . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
     Normative References  . . . . . . . . . . . . . . . . . . . . .  11
     Informative References  . . . . . . . . . . . . . . . . . . . .  13
   Appendix A.  Implementation Alternatives for ML-DSA . . . . . . .  14
   Appendix B.  ASN.1 Objects  . . . . . . . . . . . . . . . . . . .  15
     B.1.  ML-DSA-44 . . . . . . . . . . . . . . . . . . . . . . . .  15
     B.2.  ML-DSA-65 . . . . . . . . . . . . . . . . . . . . . . . .  15

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     B.3.  ML-DSA-87 . . . . . . . . . . . . . . . . . . . . . . . .  15
     B.4.  SLH-DSA-128S-SHA2 . . . . . . . . . . . . . . . . . . . .  16
     B.5.  SLH-DSA-128F-SHA2 . . . . . . . . . . . . . . . . . . . .  16
     B.6.  SLH-DSA-192S-SHA2 . . . . . . . . . . . . . . . . . . . .  16
     B.7.  SLH-DSA-192F-SHA2 . . . . . . . . . . . . . . . . . . . .  16
     B.8.  SLH-DSA-256S-SHA2 . . . . . . . . . . . . . . . . . . . .  17
     B.9.  SLH-DSA-256F-SHA2 . . . . . . . . . . . . . . . . . . . .  17
     B.10. SLH-DSA-128S-SHAKE  . . . . . . . . . . . . . . . . . . .  17
     B.11. SLH-DSA-128F-SHAKE  . . . . . . . . . . . . . . . . . . .  17
     B.12. SLH-DSA-192S-SHAKE  . . . . . . . . . . . . . . . . . . .  18
     B.13. SLH-DSA-192F-SHAKE  . . . . . . . . . . . . . . . . . . .  18
     B.14. SLH-DSA-256S-SHAKE  . . . . . . . . . . . . . . . . . . .  18
     B.15. SLH-DSA-256F-SHAKE  . . . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   The Internet Key Exchange, or IKEv2 [RFC7296], is a key agreement and
   security negotiation protocol; it is used for key establishment in
   IPsec.  In the IKE_AUTH exchange, the initiator and responder
   independently select and use their preferred authentication method,
   which may differ between peers.  The most common authentication
   method is digital signatures using asymmetric cryptography.
   Currently, traditional digital signatures are defined for use within
   IKE_AUTH: RSA signatures, Elliptic Curve Digital Signature Algorithm
   (ECDSA) [RFC4754], and Edwards-curve Digital Signature Algorithm
   (EdDSA) [RFC8420].

   The existence of a Cryptographically Relevant Quantum Computer (CRQC)
   would render traditional asymmetric algorithms obsolete and insecure.
   This is because the assumptions about the intractability of the
   mathematical problems these algorithms rely on, which offer confident
   levels of security today, no longer apply in the existence of a CRQC.
   Consequently, there is a requirement to update protocols and
   infrastructure to use post-quantum algorithms.  Post-quantum
   algorithms are asymmetric algorithms designed to be secure against
   CRQCs as well as classical computers.  The traditional cryptographic
   primitives that need to be replaced by post-quantum cryptographic
   (PQC) algorithms are discussed in PQC for Engineers [RFC9958].

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   This document defines a general approach to incorporating PQC digital
   signature algorithms into IKEv2 while maintaining interoperability
   and backward compatibility, as it does not change the IKEv2 protocol
   but adds negotiable PQC signature algorithms.  Additionally, it
   outlines how Module-Lattice-Based Digital Signatures (ML-DSA)
   [FIPS204] and Stateless Hash-Based Digital Signatures (SLH-DSA)
   [FIPS205] can be employed as authentication methods within IKEv2, as
   they have been standardized by the US National Institute of Standards
   and Technology (NIST) PQC project.

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.

   For the purposes of this document, it is helpful to be able to divide
   cryptographic algorithms into two classes:

   "Asymmetric Traditional Cryptographic Algorithm": An asymmetric
   cryptographic algorithm based on integer factorisation, finite field
   discrete logarithms, elliptic curve discrete logarithms, or related
   mathematical problems.

   "Post-Quantum Algorithm": An asymmetric cryptographic algorithm that
   is believed to be secure against attacks using quantum computers as
   well as classical computers.  Post-quantum algorithms can also be
   called quantum-resistant or quantum-safe algorithms.  Examples of
   quantum-resistant digital signature schemes include ML-DSA and SLH-
   DSA.

3.  General Framework for PQC Authentication in IKEv2

   IKEv2 authentication commonly relies on digital signatures to verify
   the identity of communicating peers.  The mechanism described in this
   document enables the use of any PQC digital signature algorithm
   without modifying core IKEv2 operations.

3.1.  Specifying PQC Signature Algorithms

   *  IKEv2 can use arbitrary signature algorithms as described in
      Signature Authentication in IKEv2 [RFC7427], where the "Digital
      Signature" authentication method supersedes previously defined
      signature authentication methods.  Any PQC digital signature
      algorithm can be incorporated using the "Digital Signature"
      authentication method, as defined in [RFC7427].

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   *  Distinguished Encoding Rules (DER) encoded AlgorithmIdentifier
      ASN.1 objects will be used to uniquely identify the PQC signature
      algorithm scheme and the parameter set associated with it.  The
      AlgorithmIdentifier ASN.1 object is placed in the Authentication
      Data field of the Authentication payload (see Figure 2 of
      [RFC7427] for details).

3.2.  Signature Generation and Verification

   PQC signatures may be generated in either deterministic or hedged
   modes.  The terms deterministic and hedged used in this document are
   in accordance with ML-DSA [FIPS204] and SLH-DSA [FIPS205], which
   define the ML-DSA and SLH-DSA algorithms, respectively.  Future PQC
   signature algorithms may adopt different nomenclature, but will be
   expected to follow the same principles.

   In the deterministic mode, the signature is derived entirely from the
   message and the signer’s private key, without introducing fresh
   randomness at signing time.  While this eliminates reliance on an
   external random number generator, it increases susceptibility to
   side-channel attacks, particularly fault injection attacks.

   The hedged mode provides some resistance against this risk by
   including precomputed randomness in the signer's private key and
   incorporating fresh randomness generated at signing time.  This foils
   some side channel attack approaches, while adding no additional
   strength against others.  If protection against side-channel attacks
   is required, ML-DSA implementations that implement side-channel
   resistance should be used.

   In the context of signature-based authentication in IKEv2, the data
   used for generating a digital signature is unique for each session,
   as it includes session-specific information such as nonces.  PQC
   signature algorithms can leverage the hedged variant within IKEv2 to
   enhance security against side-channel attacks.  The choice between
   deterministic and hedged signing modes does not impact
   interoperability because the verification process remains the same
   for both variants.

   If the PQC signature algorithm uses a 'context' input parameter, it
   MUST be set to an empty string.

   Certain digital signature algorithms support two modes: "pure" mode
   and "pre-hash" mode.  For example, ML-DSA and SLH-DSA support both
   modes.  In pure mode, the content is signed directly along with some
   domain separation information.  In contrast, pre-hash mode involves
   signing a digest of the message.  This document specifies the use of
   pure mode for signature-based authentication in IKEv2, where the

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   message is signed directly along with domain separation information.
   The data used for authentication in IKEv2, as described in
   Section 2.15 of IKEv2 [RFC7296], consists of elements such as nonces,
   SPIs, and initial exchange messages (messages preceding IKE_AUTH),
   which are typically within device memory constraints.

3.2.1.  Handling PQC Signatures in IKEv2

   As specified in Signature Authentication in IKEv2 [RFC7427], both the
   initiator and responder MUST send the SIGNATURE_HASH_ALGORITHMS
   notify payload in the IKE_SA_INIT exchange to indicate the set of
   hash algorithms they support for signature generation and
   verification.  The SIGNATURE_HASH_ALGORITHMS notify payload contains
   a list of 2-octet hash algorithm identifiers, defined in the IANA
   "IKEv2 Hash Algorithms" registry [IANA-IKEv2-Hash].

   For PQC signature algorithms that inherently operate directly on the
   raw message without hashing, such as ML-DSA and SLH-DSA, only the
   'Identity' hash function is applicable.  The 'Identity' hash function
   (value 5) is defined in Section 2 of "Using the Edwards-Curve Digital
   Signature Algorithm (EdDSA) in the Internet Key Exchange Protocol
   Version 2 (IKEv2)" [RFC8420] and indicates that the input message is
   used as-is, without any hash function applied.  Therefore,
   implementations supporting such PQC signature algorithms MUST include
   the 'Identity' hash (5) in the SIGNATURE_HASH_ALGORITHMS
   notification.  Furthermore, PQC signature algorithms requiring the
   'Identity' hash MUST NOT be used with a peer that has not indicated
   support for the Identity hash in its notify payload.

   When generating a signature with a PQC signature algorithm, the IKEv2
   implementation takes the InitiatorSignedOctets string or the
   ResponderSignedOctets string (as appropriate), logically sends it to
   the identity hash (which leaves it unchanged), and then passes it
   into the PQC signer as the message to be signed (with empty context
   string, if applicable).  The resulting signature is placed into the
   Signature Value field of the Authentication Payload.

   When verifying a signature with a PQC signature algorithm, the IKEv2
   implementation takes the InitiatorSignedOctets string or the
   ResponderSignedOctets string (as appropriate), logically sends it to
   the identity hash (which leaves it unchanged), and then passes it
   into the PQC signature verifier as the message to be verified (with
   empty context string, if applicable).

   IKEv2 peers supporting the PQC authentication mechanism defined in
   this specification MUST implement IKEv2 message fragmentation
   [RFC7383], unless IKEv2 runs over a reliable transport (e.g.,
   [RFC9329]) or the underlying network is known to support sufficiently

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   large MTUs without fragmentation issues, since PQC public keys and
   signatures can be significantly larger than those used in traditional
   algorithms.  For example, ML-DSA-44 requires a public key of 1,312
   bytes and a signature of 2,420 bytes, while even the smallest SLH-DSA
   signature is around 7,856 bytes.  As guidance, IKEv2 peers should
   assume a minimum PMTU of 1280 bytes for IPv6 (per [RFC8200]) and,
   where legacy IPv4 networks are a consideration, an effective MTU of
   576 bytes for IPv4 (per [RFC1122]).

3.3.  Mechanisms for Signaling Supported Key Pair Types

   The following mechanisms can be used by peers to signal the types of
   digital signature algorithms and parameters they support:

   *  Certificate Request Payload: One method to ascertain that the key
      pair type the initiator wants the responder to use is through a
      Certificate Request payload (defined in Section 3.7 of IKEv2
      [RFC7296]) sent by the initiator.  For example, the initiator can
      specify that it trusts certificates issued by a certificate
      authority (CA) that signs with a particular PQC signature
      algorithm.  This implies that the initiator can process signatures
      generated using that algorithm, thereby allowing the responder to
      authenticate itself using a key pair associated with the specified
      PQC signature scheme.

   *  Authentication Method Announcement: Using "Announcing Supported
      Authentication Methods in the Internet Key Exchange Protocol
      Version 2 (IKEv2)" [RFC9593], which enables peers to declare their
      supported authentication methods.  This improves interoperability
      when IKEv2 peers are configured with multiple credential types to
      authenticate each other.  The responder includes a
      SUPPORTED_AUTH_METHODS notification in the IKE_SA_INIT response
      message, listing the signature scheme(s) it supports under the
      Digital Signature authentication method.  The initiator includes
      the SUPPORTED_AUTH_METHODS notification in either the IKE_AUTH
      request message or in the IKE_INTERMEDIATE request.  This
      notification lists the digital signature scheme(s) supported by
      the initiator, ordered by preference.

   In traditional IKEv2 deployments, peers often implicitly know the
   signature algorithms in use based on pre-configured certificates,
   trusted CAs, and IKEv2 policies.  However, cryptographic agility, the
   ability to negotiate and use different cryptographic algorithms, is
   gaining increased attention for ensuring long-term security and
   interoperability.  This requirement becomes even more relevant with
   the introduction of PQC algorithms, where multiple signature
   algorithms with varying security levels and performance
   characteristics may need to be supported over time.

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4.  Specifying ML-DSA within IKEv2

   ML-DSA [FIPS204] is a digital signature algorithm based on the
   hardness lattice problems over module lattices (i.e., the Module
   Learning with Errors problem (commonly referred to as MLWE)).  The
   design of the algorithm is based on the "Fiat-Shamir with Aborts"
   [Lyu09] framework introduced by Lyubashevsky that leverages rejection
   sampling to render lattice-based Fiat-Shamir (FS) schemes compact and
   secure.  ML-DSA uses a uniform distribution over small integers for
   computing coefficients in error vectors, which simplifies
   implementation compared to schemes requiring discrete Gaussian
   sampling.

   ML-DSA is instantiated with three parameter sets for the PQ Security
   Levels 2, 3, and 5 (see Table 2 in Section 11 of PQC for Engineers
   [RFC9958]).  Security properties of ML-DSA are discussed in Section 9
   of PKIX Algorithm Identifiers for ML-DSA [RFC9881].  This document
   specifies the use of the ML-DSA algorithm in IKEv2 at three security
   levels: ML-DSA-44, ML-DSA-65, and ML-DSA-87.  The DER encodings of
   the AlgorithmIdentifier objects for ML-DSA-44, ML-DSA-65, and ML-
   DSA-87 are listed in Appendix B.

5.  Specifying SLH-DSA within IKEv2

   SLH-DSA [FIPS205] utilizes the concept of stateless hash-based
   signatures.  In contrast to stateful signature algorithms such as the
   eXtended Merkle Signature Scheme (XMSS) [RFC8391] or Hierarchical
   Signature System/Leighton-Micali Signature (HSS/LMS) [RFC8554], SLH-
   DSA eliminates the need for maintaining state information during the
   signing process.  SLH-DSA is designed to sign up to 2^64 messages and
   it offers three security levels.  The parameters for PQ Security
   Levels 1, 3, and 5 were chosen to provide AES-128, AES-192, and
   AES-256 bits of security respectively (see Table 2 in Section 11 of
   PQC for Engineers [RFC9958]).  This document specifies the use of the
   SLH-DSA algorithm in IKEv2 at each level.

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   Each security level (1, 3, and 5) defines two variants of the
   algorithm: a small (S) version and a fast (F) version.  The small
   version prioritizes smaller signature sizes, making them suitable for
   resource-constrained IoT devices.  Conversely, the fast version
   prioritizes speed over signature size, minimizing the time required
   to generate signatures.  However, signature verification with the
   small version is faster than with the fast version.  For hash
   function selection, the algorithm uses SHA-256 ([FIPS180]) for
   security level 1 and both SHA-256 and SHA-512 ([FIPS180]) for
   security levels 3 and 5.  Alternatively, SHAKE256 ([FIPS202]) can be
   used across all security levels.  Those hash function selections are
   internal to SLH-DSA implementations, and are not to be confused with
   those in the SIGNATURE_HASH_ALGORITHMS notification payload.

   ML-DSA outperforms SLH-DSA in both signature generation and
   validation time, as well as signature size.  SLH-DSA, in contrast,
   offers smaller key sizes but larger signature sizes.

   The following combinations are defined in SLH-DSA [FIPS205]:

   *  SLH-DSA-128S-SHA2

   *  SLH-DSA-128F-SHA2

   *  SLH-DSA-192S-SHA2

   *  SLH-DSA-192F-SHA2

   *  SLH-DSA-256S-SHA2

   *  SLH-DSA-256F-SHA2

   *  SLH-DSA-128S-SHAKE

   *  SLH-DSA-128F-SHAKE

   *  SLH-DSA-192S-SHAKE

   *  SLH-DSA-192F-SHAKE

   *  SLH-DSA-256S-SHAKE

   *  SLH-DSA-256F-SHAKE

   SLH-DSA does not introduce a new hardness assumption beyond those
   inherent to the underlying hash functions.  It builds upon
   established foundations in cryptography, making it a reliable and
   robust digital signature scheme in the face of a CRQC.  While attacks

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   on lattice-based schemes like ML-DSA are hypothetical as of 2026,
   such attacks, if realized, could compromise their security.  SLH-DSA
   would remain unaffected by these attacks due to its distinct
   mathematical foundations.  This ensures the continued security of
   systems and protocols that utilize SLH-DSA for digital signatures.

   The DER encodings of the AlgorithmIdentifier objects for each SLH-DSA
   variant are listed in Appendix B.

6.  Use of ML-DSA and SLH-DSA

   Both ML-DSA [FIPS204] and SLH-DSA [FIPS205] define deterministic and
   hedged signing modes, where the hedged mode incorporates fresh
   randomness into the signing procedure.  IKEv2 peers can use either
   mode of ML-DSA and SLH-DSA for authentication in IKEv2, with a
   preference for the hedged mode (Section 3.2).  The signing mode is a
   local decision made by the signer; it is not negotiated between the
   peers, and the verifier neither knows nor needs to know which mode
   was used, since verification is identical in both cases.

   The three security levels of ML-DSA are identified via
   AlgorithmIdentifier ASN.1 objects, as specified in NIST [CSOR] and
   referenced in PKIX Algorithm Identifiers for the ML-DSA [RFC9881].
   [FIPS204] defines both a pure and a pre-hash variant of ML-DSA, but
   PKIX Algorithm Identifiers for the ML-DSA [RFC9881] specifies only
   the pure variant.

   The different parameter sets of SLH-DSA are identified via
   AlgorithmIdentifier ASN.1 objects, as specified in NIST [CSOR] and
   referenced in PKIX Algorithm Identifiers for the SLH-DSA [RFC9909].
   [FIPS205] defines both a pure and a pre-hash mode of SLH-DSA, but
   this document specifies the use of only Pure SLH-DSA, consistent with
   Section 3.2.

7.  IANA Considerations

   This document makes no requests to IANA.

8.  Security Considerations

   PQC signature algorithms are generally modeled to achieve strong
   unforgeability under adaptive chosen-message attacks (SUF-CMA; see
   Section 10.1.1 of PQC for Engineers [RFC9958]).  For example, ML-DSA
   provides SUF-CMA security.  However, some algorithms, such as SLH-
   DSA, achieve existential unforgeability under chosen-message attacks
   (EUF-CMA; see Section 10.1.1 of PQC for Engineers [RFC9958]).  This
   distinction does not impact IKEv2, as the signed data in each session
   is unique due to the inclusion of nonces.  Consequently, the oracle-

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   based forgery attack scenarios in the EUF-CMA model do not arise in
   IKEv2.

   Different PQC signature schemes are designed to provide security
   levels comparable to well-established cryptographic primitives.  For
   example, some schemes align with the US NIST post-quantum security
   categories (Categories 1 through 5) as discussed in ML-DSA [FIPS204]
   and SLH-DSA [FIPS205].  These categories specify target security
   strengths that correspond approximately to exhaustive key-search
   resistance for AES-128, AES-192, and AES-256, and collision-search
   resistance for SHA-256, SHA-384, and SHA-512.  The choice of a PQC
   signature algorithm should be guided by the desired security level
   and performance requirements.

   ML-DSA-44, ML-DSA-65, and ML-DSA-87 are designed to offer security
   comparable with the SHA-256/SHA3-256 collision resistance (which is a
   harder problem than AES-128 key search), AES-192 key search, and
   AES-256 key search, respectively.  Similarly, SLH-DSA-
   128{S,F}-{SHA2,SHAKE}, SLH-DSA-192{S,F}-{SHA2,SHAKE}, and SLH-DSA-
   256{S,F}-{SHA2,SHAKE} are designed to offer security comparable with
   the AES-128, AES-192, and AES-256 respectively.

   The Security Considerations section of PKIX Algorithm Identifiers for
   ML-DSA [RFC9881] and PKIX Algorithm Identifiers for SLH-DSA [RFC9909]
   apply to this specification as well.

   SLH-DSA keys are limited to 2^64 signatures.  This upper bound is so
   large that even a IKEv2 server establishing IKEv2 sessions at an
   extremely high rate could not realistically reach it (at 10 billion
   signatures per second, it would still take over 58 years).  The limit
   is therefore of theoretical interest only, but implementations may
   still track signature usage as a precautionary security measure.  ML-
   DSA does not have a built-in signature limit, allowing for an
   arbitrary number of signatures to be made with the same key.

Acknowledgements

   Thanks to Stefaan De Cnodder, Loganaden Velvindron, Paul Wouters,
   Andreas Steffen, Dan Wing, Wang Guilin, Rebecca Guthrie, Jonathan
   Hammell, Eric Vyncke, John Mattsson, Russ Housley, Tony Li, Tero
   Kivinen and Daniel Van Geest for the discussion and comments.

References

Normative References

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   [CSOR]     US NIST, "Computer Security Objects Register", 20 August
              2024, <https://csrc.nist.gov/projects/computer-security-
              objects-register/algorithm-registration>.

   [FIPS180]  "US NIST, Secure Hash Standard (SHS), FIPS PUB 180-4,
              August 2015", <https://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.180-4.pdf>.

   [FIPS202]  "US NIST, SHA-3 Standard: Permutation-Based Hash and
              Extendable-Output Functions, FIPS PUB 202, August 2015.",
              <https://nvlpubs.nist.gov/nistpubs/fips/
              nist.fips.202.pdf>.

   [FIPS204]  "FIPS 204: Module-Lattice-Based Digital Signature
              Standard", <https://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.204.pdf>.

   [FIPS205]  "FIPS 205: Stateless Hash-Based Digital Signature
              Standard", <https://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.205.pdf>.

   [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>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <https://www.rfc-editor.org/rfc/rfc7296>.

   [RFC7383]  Smyslov, V., "Internet Key Exchange Protocol Version 2
              (IKEv2) Message Fragmentation", RFC 7383,
              DOI 10.17487/RFC7383, November 2014,
              <https://www.rfc-editor.org/rfc/rfc7383>.

   [RFC7427]  Kivinen, T. and J. Snyder, "Signature Authentication in
              the Internet Key Exchange Version 2 (IKEv2)", RFC 7427,
              DOI 10.17487/RFC7427, January 2015,
              <https://www.rfc-editor.org/rfc/rfc7427>.

   [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>.

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   [RFC8420]  Nir, Y., "Using the Edwards-Curve Digital Signature
              Algorithm (EdDSA) in the Internet Key Exchange Protocol
              Version 2 (IKEv2)", RFC 8420, DOI 10.17487/RFC8420, August
              2018, <https://www.rfc-editor.org/rfc/rfc8420>.

   [RFC9593]  Smyslov, V., "Announcing Supported Authentication Methods
              in the Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 9593, DOI 10.17487/RFC9593, July 2024,
              <https://www.rfc-editor.org/rfc/rfc9593>.

Informative References

   [IANA-IKEv2-Hash]
              IANA, "Internet Key Exchange Version 2 (IKEv2) Parameters.
              IKEv2 Hash Algorithms", <https://www.iana.org/assignments/
              ikev2-parameters/ikev2-parameters.xhtml#hash-algorithms>.

   [Lyu09]    "V. Lyubashevsky, “Fiat-Shamir With Aborts: Applications
              to Lattice and Factoring-Based Signatures“, ASIACRYPT
              2009", <https://www.iacr.org/archive/
              asiacrypt2009/59120596/59120596.pdf>.

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,
              <https://www.rfc-editor.org/rfc/rfc1122>.

   [RFC4754]  Fu, D. and J. Solinas, "IKE and IKEv2 Authentication Using
              the Elliptic Curve Digital Signature Algorithm (ECDSA)",
              RFC 4754, DOI 10.17487/RFC4754, January 2007,
              <https://www.rfc-editor.org/rfc/rfc4754>.

   [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>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/rfc/rfc8200>.

   [RFC8391]  Huelsing, A., Butin, D., Gazdag, S., Rijneveld, J., and A.
              Mohaisen, "XMSS: eXtended Merkle Signature Scheme",
              RFC 8391, DOI 10.17487/RFC8391, May 2018,
              <https://www.rfc-editor.org/rfc/rfc8391>.

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   [RFC8554]  McGrew, D., Curcio, M., and S. Fluhrer, "Leighton-Micali
              Hash-Based Signatures", RFC 8554, DOI 10.17487/RFC8554,
              April 2019, <https://www.rfc-editor.org/rfc/rfc8554>.

   [RFC9329]  Pauly, T. and V. Smyslov, "TCP Encapsulation of Internet
              Key Exchange Protocol (IKE) and IPsec Packets", RFC 9329,
              DOI 10.17487/RFC9329, November 2022,
              <https://www.rfc-editor.org/rfc/rfc9329>.

   [RFC9881]  Massimo, J., Kampanakis, P., Turner, S., and B. E.
              Westerbaan, "Internet X.509 Public Key Infrastructure --
              Algorithm Identifiers for the Module-Lattice-Based Digital
              Signature Algorithm (ML-DSA)", RFC 9881,
              DOI 10.17487/RFC9881, October 2025,
              <https://www.rfc-editor.org/rfc/rfc9881>.

   [RFC9909]  Bashiri, K., Fluhrer, S., Gazdag, S., Van Geest, D., and
              S. Kousidis, "Internet X.509 Public Key Infrastructure --
              Algorithm Identifiers for the Stateless Hash-Based Digital
              Signature Algorithm (SLH-DSA)", RFC 9909,
              DOI 10.17487/RFC9909, December 2025,
              <https://www.rfc-editor.org/rfc/rfc9909>.

   [RFC9958]  Banerjee, A., Reddy.K, T., Schoinianakis, D., Hollebeek,
              T., and M. Ounsworth, "Post-Quantum Cryptography for
              Engineers", RFC 9958, DOI 10.17487/RFC9958, June 2026,
              <https://www.rfc-editor.org/rfc/rfc9958>.

Appendix A.  Implementation Alternatives for ML-DSA

   With ML-DSA, there are two different approaches to implementing the
   signature process.  The first one is to provide the SignedOctets
   string to the cryptographic library to generate the full signature;
   this works for SLH-DSA as well.

   The second approach involves using the Externalμ-ML-DSA API allowed
   by [FIPS204]; specifically by the comment to line 6 of algorithm 7 of
   FIPS 204.  In this method, the implementation calls the External μ
   pre-hashing mode with the SignedOctets string and the ML-DSA public
   key, which externalizes the message pre-hashing originally performed
   inside the signing operation (see Appendix D of [RFC9881] for ML-DSA
   pre-hashing).  The resulting μ value is then passed to the
   cryptographic library to execute the Externalμ-ML-DSA.Sign API, which
   uses μ and the ML-DSA private key to produce the signature.  This
   document specifies only the use of ML-DSA's External μ mode and does
   not use HashML-DSA.  This approach avoids requiring large message
   inputs to be processed within potentially constrained cryptographic
   modules, such as Hardware Security Modules (HSMs).

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   Both approaches are considered "pure" mode and produce the same ML-
   DSA signature and are fully interoperable.  The choice between them
   depends on implementation preferences, such as whether the External μ
   pre-hashing step is handled internally by the cryptographic module or
   performed explicitly by the IKEv2 implementation.

Appendix B.  ASN.1 Objects

   This section lists AlgorithmIdentifier ASN.1 objects for algorithms
   mentioned in the document in binary form.
   This section is not normative, and these values should only be used
   as examples.  If the ASN.1 object listed in this section and the
   ASN.1 object specified by the algorithm differ, then the algorithm
   specification must be used.

   The generic format for the AlgorithmIdentifier ASN.1 object is
   defined in Section 4.1.1.2 of PKIX [RFC5280].

B.1.  ML-DSA-44

   id-ml-dsa-44 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16)
   us(840) organization(1) gov(101) csor(3) nistAlgorithm(4) sigAlgs(3)
   id-ml-dsa-44(17) }

   Parameters are absent.

   Name = id-ml-dsa-44, oid = 2.16.840.1.101.3.4.3.17
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 11

B.2.  ML-DSA-65

   id-ml-dsa-65 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16)
   us(840) organization(1) gov(101) csor(3) nistAlgorithm(4) sigAlgs(3)
   id-ml-dsa-65(18) }

   Parameters are absent.

   Name = id-ml-dsa-65, oid = 2.16.840.1.101.3.4.3.18
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 12

B.3.  ML-DSA-87

   id-ml-dsa-87 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16)
   us(840) organization(1) gov(101) csor(3) nistAlgorithm(4) sigAlgs(3)
   id-ml-dsa-87(19) }

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   Parameters are absent.

   Name = id-ml-dsa-87, oid = 2.16.840.1.101.3.4.3.19
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 13

B.4.  SLH-DSA-128S-SHA2

   id-slh-dsa-sha2-128s OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-sha2-128s(20) }

   Parameters are absent.

   Name = id-slh-dsa-sha2-128s, oid = 2.16.840.1.101.3.4.3.20
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 14

B.5.  SLH-DSA-128F-SHA2

   id-slh-dsa-sha2-128f OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-sha2-128f(21) }

   Parameters are absent.

   Name = id-slh-dsa-sha2-128f, oid = 2.16.840.1.101.3.4.3.21
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 15

B.6.  SLH-DSA-192S-SHA2

   id-slh-dsa-sha2-192s OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-sha2-192s(22) }

   Parameters are absent.

   Name = id-slh-dsa-sha2-192s, oid = 2.16.840.1.101.3.4.3.22
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 16

B.7.  SLH-DSA-192F-SHA2

   id-slh-dsa-sha2-192f OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-sha2-192f(23) }

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   Parameters are absent.

   Name = id-slh-dsa-sha2-192f, oid = 2.16.840.1.101.3.4.3.23
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 17

B.8.  SLH-DSA-256S-SHA2

   id-slh-dsa-sha2-256s OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-sha2-256s(24) }

   Parameters are absent.

   Name = id-slh-dsa-sha2-256s, oid = 2.16.840.1.101.3.4.3.24
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 18

B.9.  SLH-DSA-256F-SHA2

   id-slh-dsa-sha2-256f OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-sha2-256f(25) }

   Parameters are absent.

   Name = id-slh-dsa-sha2-256f, oid = 2.16.840.1.101.3.4.3.25
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 19

B.10.  SLH-DSA-128S-SHAKE

   id-slh-dsa-shake-128s OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-shake-128s(26) }

   Parameters are absent.

   Name = id-slh-dsa-shake-128s, oid = 2.16.840.1.101.3.4.3.26
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 1a

B.11.  SLH-DSA-128F-SHAKE

   id-slh-dsa-shake-128f OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-shake-128f(27) }

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   Parameters are absent.

   Name = id-slh-dsa-shake-128f, oid = 2.16.840.1.101.3.4.3.27
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 1b

B.12.  SLH-DSA-192S-SHAKE

   id-slh-dsa-shake-192s OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-shake-192s(28) }

   Parameters are absent.

   Name = id-slh-dsa-shake-192s, oid = 2.16.840.1.101.3.4.3.28
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 1c

B.13.  SLH-DSA-192F-SHAKE

   id-slh-dsa-shake-192f OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-shake-192f(29) }

   Parameters are absent.

   Name = id-slh-dsa-shake-192f, oid = 2.16.840.1.101.3.4.3.29
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 1d

B.14.  SLH-DSA-256S-SHAKE

   id-slh-dsa-shake-256s OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-shake-256s(30) }

   Parameters are absent.

   Name = id-slh-dsa-shake-256s, oid = 2.16.840.1.101.3.4.3.30
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 1e

B.15.  SLH-DSA-256F-SHAKE

   id-slh-dsa-shake-256f OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
   country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4)
   sigAlgs(3) id-slh-dsa-shake-256f(31) }

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   Parameters are absent.

   Name = id-slh-dsa-shake-256f, oid = 2.16.840.1.101.3.4.3.31
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 1f

Authors' Addresses

   Tirumaleswar Reddy
   Nokia
   Bangalore
   Karnataka
   India
   Email: kondtir@gmail.com

   Valery Smyslov
   ELVIS-PLUS
   Russian Federation
   Email: svan@elvis.ru

   Scott Fluhrer
   Cisco Systems
   Email: sfluhrer@cisco.com

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