



sshm                                                           R. Petrov
Internet-Draft                                              October 2025
Updates: 4253 (if approved)                                             
Intended status: Standards Track                                        
Expires: 12 April 2026


    ML-DSA Public Key Algorithms for the Secure Shell (SSH) Protocol
                         draft-rpe-ssh-mldsa-01

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.

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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   This Internet-Draft will expire on 4 April 2026.

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   document authors.  All rights reserved.

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   provided without warranty as described in the Revised BSD License.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   3.  Public Key Algorithm  . . . . . . . . . . . . . . . . . . . .   3
   4.  Public Key Format . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Signature Algorithm . . . . . . . . . . . . . . . . . . . . .   3
   6.  Signature Format  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Verification Algorithm  . . . . . . . . . . . . . . . . . . .   4
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   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
   "ssh-mldsa-44", "ssh-mldsa-65", and "ssh-mldsa-87".  Those algorithms
   correspond to the Table 1.  "ML-DSA parameter sets" defined in
   [FIPS-204] Section 4 "Parameter Sets".

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.








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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 "ssh-
   mldsa-44", "ssh-mldsa-65", and "ssh-mldsa-87".  Those 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 SHOULDimplement "ssh-mldsa-65"
   signature algorithm.  It MAY implement "ssh-mldsa-44" and "ssh-mldsa-
   87" signature algorithms.

4.  Public Key Format

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

      string  "ssh-mldsa-44"

      string  key

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

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

      string  "ssh-mldsa-65"

      string  key

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

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

      string  "ssh-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).



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6.  Signature Format

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

      string  "ssh-mldsa-44"

      string  signature

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

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

      string  "ssh-mldsa-65"

      string  signature

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

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

      string  "ssh-mldsa-87"

      string  signature

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

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:






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

   [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>.






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   [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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