



sshm                                                           R. Petrov
Internet-Draft                                           19 October 2025
Updates: 4253 (if approved)                                             
Intended status: Standards Track                                        
Expires: 22 April 2026


    ML-DSA Public Key Algorithms for the Secure Shell (SSH) Protocol
                         draft-rpe-ssh-mldsa-02

Abstract

   This document describes the use of the ML-DSA digital signature
   algorithms in the Secure Shell (SSH) protocol.  Accordingly, this RFC
   updates RFC 4253.

Document and implementation details

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

   The datatracker status page of the draft is draft-rpe-ssh-mldsa
   (https://datatracker.ietf.org/doc/draft-rpe-ssh-mldsa).

   The source of this document is located at I-D ssh-mldsa
   (https://gitlab.com/secsh/pkixssh/-/blob/mldsa_demo/draft-rpe-ssh-
   mldsa.xml).  Implementation could be found at PKIX-SSHMLDSA-DEMO
   (https://gitlab.com/secsh/pkixssh/-/tree/mldsa_demo) branch.

   Discussion of this document takes place on the Secure Shell
   Maintenance (sshm)" (https://datatracker.ietf.org/group/sshm/about)
   mailing list (mailto:ssh@ietf.org) which is archived here
   (https://mailarchive.ietf.org/arch/browse/ssh/).

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."




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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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Public Key Algorithm  . . . . . . . . . . . . . . . . . . . .   3
   4.  Public Key Format . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Signature Algorithm . . . . . . . . . . . . . . . . . . . . .   4
   6.  Signature Format  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Verification Algorithm  . . . . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   5
     10.2.  Informative References . . . . . . . . . . . . . . . . .   6
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Secure Shell (SSH) [RFC4251] is a secure remote-login protocol.  It
   provides for an extensible variety of public key algorithms for
   identifying servers and users to one another.

   This document describes the use of ML-DSA algorithms to be
   implemented by Secure Shells (SSH) and standardize the use of names
   *mldsa-44*, *mldsa-65*, and *mldsa-87*. These algorithms correspond
   to the Table 1.  "ML-DSA parameter sets" defined in [FIPS-204]
   Section 4 "Parameter Sets".






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2.  Conventions Used in This Document

   The descriptions of key and signature formats use the notation
   introduced in [RFC4251], Section 3 and the string data type from
   [RFC4251], Section 5.

2.1.  Requirements Language

   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.  Public Key Algorithm

   This document describes a public key algorithms for use with SSH, as
   per [RFC4253], Section 6.6.  The name of the algorithms are *mldsa-
   44*, *mldsa-65*, and *mldsa-87*. These algorithms only supports
   signing and not encryption.  Keys are generated according to the
   procedure described in [FIPS-204] Algorithm 1 step 5.

   Standard implementations of SSH SHOULD implement *mldsa-65* public
   Key algorithm.  It MAY implement *mldsa-44* and *mldsa-87* public key
   algorithms.

4.  Public Key Format

   *  The *mldsa-44* key format has the following encoding:

      string  *mldsa-44*

      string  key

      Here, 'key' is the 1312-octet public key encoded as is described
      in [FIPS-204] Algorithm 22.

   *  The *mldsa-65* key format has the following encoding:

      string  *mldsa-65*

      string  key

      Here, 'key' is the 1952-octet public key encoded as is described
      in [FIPS-204] Algorithm 22.

   *  The *mldsa-87* key format has the following encoding:




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      string  *mldsa-87*

      string  key

      Here, 'key' is the 2592-octet public key encoded as is described
      in [FIPS-204] Algorithm 22.

5.  Signature Algorithm

   Signatures are generated according to the procedure described in
   [FIPS-204].  Signature generation should use normal signing process
   (Pure ML-DSA Signature Generation) with empty string as context
   parameter.  The process is defined in [FIPS-204] Algorithm 2 step
   10(sign) and Algorithm 3 step 5(verify).

6.  Signature Format

   *  The *mldsa-44* public key algorithm has the following format for
      encoding the signature:

      string  *mldsa-44*

      string  signature

      Here, 'signature' is the 2420-octet signature produced in
      accordance with [FIPS-204] Algorithm 2.

   *  The *mldsa-65* public key algorithm has the following format for
      encoding the signature:

      string  *mldsa-65*

      string  signature

      Here, 'signature' is the 3309-octet signature produced in
      accordance with [FIPS-204] Algorithm 2.

   *  The *mldsa-87* public key algorithm has the following format for
      encoding the signature:

      string  *mldsa-87*

      string  signature

      Here, 'signature' is the 4627-octet signature produced in
      accordance with [FIPS-204] Algorithm 2.





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7.  Verification Algorithm

   ML-DSA signatures are verified according to the procedure in
   [FIPS-204] Algorithm 3 step 5.

8.  IANA Considerations

   This document augments the Public Key Algorithm Names in [RFC4250],
   Section 4.11.3.

   This document requests new entries to "Public Key Algorithm Names" in
   the "Secure Shell (SSH) Protocol Parameters" registry [IANA-SSH]
   according to the procedures in [RFC9519], Section 3:

              +===========================+================+
              | Public Key Algorithm Name | Reference      |
              +===========================+================+
              | mldsa-44                  | This document. |
              +---------------------------+----------------+
              | mldsa-65                  | This document. |
              +---------------------------+----------------+
              | mldsa-87                  | This document. |
              +---------------------------+----------------+

                                 Table 1

9.  Security Considerations

   The security considerations in [RFC4251], Section 9 apply to all SSH
   implementations, including those using ML-DSA-44, ML-DSA-65, and ML-
   DSA-87.  Also rules in [FIPS-204] Section 3.6 "Additional
   Requirements" apply as well.

10.  References

10.1.  Normative References

   [FIPS-204] "Module-lattice-based digital signature standard",
              National Institute of Standards and Technology (U.S.),
              DOI 10.6028/nist.fips.204, August 2024,
              <https://csrc.nist.gov/pubs/fips/204/final>.

   [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/info/rfc2119>.





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   [RFC4250]  Lehtinen, S. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Protocol Assigned Numbers", RFC 4250,
              DOI 10.17487/RFC4250, January 2006,
              <https://www.rfc-editor.org/info/rfc4250>.

   [RFC4251]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,
              January 2006, <https://www.rfc-editor.org/info/rfc4251>.

   [RFC4253]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
              January 2006, <https://www.rfc-editor.org/info/rfc4253>.

   [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/info/rfc8174>.

   [RFC9519]  Yee, P., "Update to the IANA SSH Protocol Parameters
              Registry Requirements", RFC 9519, DOI 10.17487/RFC9519,
              January 2024, <https://www.rfc-editor.org/info/rfc9519>.

10.2.  Informative References

   [IANA-SSH] IANA, "Secure Shell (SSH) Protocol Parameters",
              <https://www.iana.org/assignments/ssh-parameters>.

Acknowledgements

   TBD

Author's Address

   Roumen Petrov
   1750 Sofia
   Bulgaria
   Email: pkixssh@roumenpetrov.info
   URI:   https://roumenpetrov.info/secsh/














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