Network Working Group B. Harris
Internet-Draft May 4, 2016
Intended status: Informational
Expires: November 5, 2016

Ed25519 public key algorithm for the Secure Shell (SSH) protocol


This document describes the use of the Ed25519 digital signature algorithm in the Secure Shell (SSH) protocol.

Status of This Memo

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This Internet-Draft will expire on November 5, 2016.

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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. Ed25519 [I-D.irtf-cfrg-eddsa] is a digital signature system. OpenSSH 6.5 [OpenSSH-6.5] introduced support for using Ed25519 for server and user authentication. Compatible support for Ed25519 has since been added to other SSH implementations.

This document describes the method implemented by OpenSSH and others, and formalizes its use of the name "ssh-ed25519".

Comments on this draft are welcomed and should be sent to the Curdle Working Group mailing list.

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.

3. Public Key Algorithm

This document describes a public key algorithm for use with SSH in accordance with [RFC4253], Section 6.6. The name of the algorithm is "ssh-ed25519". This algorithm only supports signing and not encryption.

4. Public Key Format

The "ssh-ed25519" key format has the following encoding:

   string    "ssh-ed25519"
   string    key

Here 'key' is the 32-octet public key described by [I-D.irtf-cfrg-eddsa], Section 5.1.5.

5. Signature Algorithm

Signatures are generated according to the procedure in [I-D.irtf-cfrg-eddsa], Section 5.1.6.

6. Signature format

The corresponding signature format is:

   string    "ssh-ed25519"
   string    signature

Here 'signature' is the 64-octet signature produced in accordance with [I-D.irtf-cfrg-eddsa], Section 5.1.6.

7. Verification Algorithm

Signatures are verified according to the procedure in [I-D.irtf-cfrg-eddsa], Section 5.1.7.

8. SSHFP DNS resource records

The generation of SSHFP resource records for "ssh-ed25519" keys is described in [RFC7479].

9. IANA Considerations

IANA is requested to assign the Public Key Algorithm name "ssh‑ed25519" in accordance with [RFC4250], Section 4.6.2:

Public Key Algorithm Name Reference
ssh-ed25519 [RFCXXXX]

[TO BE REMOVED: This registration should take place at the following location: <>]

10. Security Considerations

The security considerations in [RFC4251], Section 9 apply to all SSH implementations, including those using Ed25519.

The security considerations in [I-D.irtf-cfrg-eddsa], Section 10 apply to all uses of Ed25519, including those in SSH.

11. Acknowledgements

The OpenSSH implementation of Ed25519 in SSH was written by Markus Friedl.

12. References

12.1. Normative References

[RFC4250] Lehtinen, S. and C. Lonvick, "The Secure Shell (SSH) Protocol Assigned Numbers", RFC 4250, DOI 10.17487/RFC4250, January 2006.
[RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, January 2006.
[RFC4253] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, January 2006.
[I-D.irtf-cfrg-eddsa] Josefsson, S. and I. Liusvaara, "Edwards-curve Digital Signature Algorithm (EdDSA)", Internet-Draft draft-irtf-cfrg-eddsa-05, March 2016.

12.2. Informative References

[RFC7479] Moonesamy, S., "Using Ed25519 in SSHFP Resource Records", RFC 7479, DOI 10.17487/RFC7479, March 2015.
[OpenSSH-6.5] Friedl, M., Provos, N., de Raadt, T., Steves, K., Miller, D., Tucker, D., McIntyre, J., Rice, T. and B. Lindstrom, "[OpenSSH 6.5 release notes]", January 2014.

Author's Address

Ben Harris 2A Eachard Road CAMBRIDGE, CB3 0HY UNITED KINGDOM EMail:

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