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Internet Engineering Task Force (IETF) S. Moonesamy Request for Comments: 7479 March 2015 Category: Informational ISSN: 2070-1721

              Using Ed25519 in SSHFP Resource Records

Abstract

 The Ed25519 signature algorithm has been implemented in OpenSSH.
 This document updates the IANA "SSHFP RR Types for public key
 algorithms" registry by adding an algorithm number for Ed25519.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.

 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.

 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7479.

Copyright Notice

 Copyright (c) 2015 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
 (http://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 Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Moonesamy Informational [Page 1] RFC 7479 Using Ed25519 in SSHFP RRs March 2015

Table of Contents

 1. Introduction ....................................................2
 2. Ed25519 Public Key with SHA-256 Fingerprint .....................2
 3. Security Considerations .........................................3
 4. IANA Considerations .............................................3
 5. References ......................................................3
    5.1. Normative References .......................................3
    5.2. Informative References .....................................3
 Acknowledgements ...................................................4
 Author's Address ...................................................4

1. Introduction

 The Ed25519 [Ed25519] signature algorithm, specifically
 Ed25519-SHA-512, has been implemented in OpenSSH.  RFC 4255 [RFC4255]
 defines a DNS resource record, "SSHFP", which can be used to publish
 a fingerprint of the SSH server public key in the DNS.  This document
 updates the IANA "SSHFP RR Types for public key algorithms" registry
 by adding an algorithm number for Ed25519 [Ed25519].

2. Ed25519 Public Key with SHA-256 Fingerprint

 The encoding of Ed25519 public keys is described in [Ed25519].  In
 brief, an Ed25519 public key is a 32-octet value representing a
 255-bit y-coordinate of an elliptic curve point, and a sign bit
 indicating the corresponding x-coordinate.

 The SSHFP Resource Record for the Ed25519 public key with SHA-256
 fingerprint [FIPS180-4] would, for example, be:

    ssh.example.com IN SSHFP 4 2 ( a87f1b687ac0e57d2a081a2f2826723
                                   34d90ed316d2b818ca9580ea384d924
                                   01 )

 The following body of the public key file was used as input to
 generate the above fingerprint:

  ssh-ed25519
  AAAAC3NzaC1lZDI1NTE5AAAAIGPKSUTyz1HwHReFVvD5obVsALAgJRNarH4TRpNePnAS

 The opaque octet string output produced is placed as is in the RDATA
 fingerprint field.

Moonesamy Informational [Page 2] RFC 7479 Using Ed25519 in SSHFP RRs March 2015

3. Security Considerations

 The overall security of using SSHFP for SSH host key verification is
 dependent on the security policies of the SSH host administrator and
 DNS zone administrator (in transferring the fingerprint), detailed
 aspects of how verification is done in the SSH implementation, and in
 the client's diligence in accessing the DNS in a secure manner.
 Please refer to RFC 4255 [RFC4255] for a discussion of the security
 considerations.

4. IANA Considerations

 IANA has added the following entry to the "SSHFP RR Types for public
 key algorithms" registry:

    +--------+-------------+------------+
    | Value  | Description |  Reference |
    +--------+-------------+------------+
    |   4    |    Ed25519  | [RFC7479]  |
    +--------+-------------+------------+

5. References

5.1. Normative References

 [Ed25519]    Bernstein, D. J., Lange T., Schwabe P., and B-Y. Yang,
              "High-Speed High-Security Signatures", Journal of
              Cryptographic Engineering, Vol. 2, September 26, 2011.

 [RFC4255]    Schlyter, J. and W. Griffin, "Using DNS to Securely
              Publish Secure Shell (SSH) Key Fingerprints", RFC 4255,
              January 2006, <http://www.rfc-editor.org/info/rfc4255>.

5.2. Informative References

 [FIPS180-4]  National Institute of Standards and Technology, "Secure
              Hash Standard (SHS)", FIPS PUB 180-4, March 2012,
              <http://csrc.nist.gov/publications/fips/fips180-4/
              fips-180-4.pdf>.

Moonesamy Informational [Page 3] RFC 7479 Using Ed25519 in SSHFP RRs March 2015

Acknowledgements

 Some of the text in this document was written by Ondrej Sury.  The
 author would like to thank Richard Barnes, Damien Miller, Yoav Nir,
 and Paul Wouters for their feedback.  Rene Struik provided advice
 about the usage of Ed25519.  Stephen Farrell, as Security Area
 Director, reviewed the code point request.

Author's Address

 S. Moonesamy
 76, Ylang Ylang Avenue
 Quatres Bornes
 Mauritius

 EMail: sm+ietf@elandsys.com

Moonesamy Informational [Page 4]