Internet Engineering Task Force (IETF) S. Moonesamy

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: [email protected]

Moonesamy Informational [Page 4]