ML-DSA Public Key Algorithms for the Secure Shell (SSH) Protocol
draft-rpe-ssh-mldsa-02
This document is an Internet-Draft (I-D).
Anyone may submit an I-D to the IETF.
This I-D is not endorsed by the IETF and has no formal standing in the
IETF standards process.
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Roumen Petrov | ||
| Last updated | 2025-10-19 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-rpe-ssh-mldsa-02
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."
Petrov Expires 22 April 2026 [Page 1]
Internet-Draft ML-DSA for SSH October 2025
This Internet-Draft will expire on 22 April 2026.
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".
Petrov Expires 22 April 2026 [Page 2]
Internet-Draft ML-DSA for SSH October 2025
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:
Petrov Expires 22 April 2026 [Page 3]
Internet-Draft ML-DSA for SSH October 2025
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.
Petrov Expires 22 April 2026 [Page 4]
Internet-Draft ML-DSA for SSH October 2025
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>.
Petrov Expires 22 April 2026 [Page 5]
Internet-Draft ML-DSA for SSH October 2025
[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/
Petrov Expires 22 April 2026 [Page 6]