curdle R. Petrov Internet-Draft October 2025 Updates: 4253 (if approved) Intended status: Standards Track Expires: 11 April 2026 ML-DSA Public Key Algorithms for the Secure Shell (SSH) Protocol draft-rpe-ssh-mldsa-00 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. 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 4 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. Petrov Expires 11 April 2026 [Page 1] Internet-Draft ML-DSA for SSH October 2025 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. Petrov Expires 11 April 2026 [Page 2] Internet-Draft ML-DSA for SSH October 2025 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). Petrov Expires 11 April 2026 [Page 3] Internet-Draft ML-DSA for SSH October 2025 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: Petrov Expires 11 April 2026 [Page 4] Internet-Draft ML-DSA for SSH October 2025 +===========================+================+ | 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. TBD: post-quantum security considerations ... 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, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4250] Lehtinen, S. and C. Lonvick, Ed., "The Secure Shell (SSH) Protocol Assigned Numbers", RFC 4250, DOI 10.17487/RFC4250, January 2006, . [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, January 2006, . [RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, January 2006, . Petrov Expires 11 April 2026 [Page 5] Internet-Draft ML-DSA for SSH October 2025 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9519] Yee, P., "Update to the IANA SSH Protocol Parameters Registry Requirements", RFC 9519, DOI 10.17487/RFC9519, January 2024, . 10.2. Informative References [IANA-SSH] IANA, "Secure Shell (SSH) Protocol Parameters", . Acknowledgements TBD Author's Address Roumen Petrov 1750 Sofia Bulgaria Email: pkixssh@roumenpetrov.info Petrov Expires 11 April 2026 [Page 6]