Network Working Group                                          B. Harris
Internet-Draft                                               May 3, 2016
Intended status: Informational
Expires: November 4, 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 4, 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

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.

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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

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12.  References

12.1.  Normative References

   [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, <>.

              Josefsson, S. and I. Liusvaara, "Edwards-curve Digital
              Signature Algorithm (EdDSA)", draft-irtf-cfrg-eddsa-05
              (work in progress), March 2016.

12.2.  Informative References

   [RFC7479]  Moonesamy, S., "Using Ed25519 in SSHFP Resource Records",
              RFC 7479, DOI 10.17487/RFC7479, March 2015,

              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


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