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<pre>Internet Engineering Task Force (IETF) S. Moonesamy
Request for Comments: 7479 March 2015
Category: Informational
ISSN: 2070-1721
<span class="h1">Using Ed25519 in SSHFP Resource Records</span>
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 <a href="./rfc5741#section-2">Section 2 of RFC 5741</a>.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
<a href="http://www.rfc-editor.org/info/rfc7479">http://www.rfc-editor.org/info/rfc7479</a>.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
Provisions Relating to IETF Documents
(<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) 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.
<span class="grey">Moonesamy Informational [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc7479">RFC 7479</a> Using Ed25519 in SSHFP RRs March 2015</span>
Table of Contents
<a href="#section-1">1</a>. Introduction ....................................................<a href="#page-2">2</a>
<a href="#section-2">2</a>. Ed25519 Public Key with SHA-256 Fingerprint .....................<a href="#page-2">2</a>
<a href="#section-3">3</a>. Security Considerations .........................................<a href="#page-3">3</a>
<a href="#section-4">4</a>. IANA Considerations .............................................<a href="#page-3">3</a>
<a href="#section-5">5</a>. References ......................................................<a href="#page-3">3</a>
<a href="#section-5.1">5.1</a>. Normative References .......................................<a href="#page-3">3</a>
<a href="#section-5.2">5.2</a>. Informative References .....................................<a href="#page-3">3</a>
Acknowledgements ...................................................<a href="#page-4">4</a>
Author's Address ...................................................<a href="#page-4">4</a>
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
The Ed25519 [<a href="#ref-Ed25519" title=""High-Speed High-Security Signatures"">Ed25519</a>] signature algorithm, specifically
Ed25519-SHA-512, has been implemented in OpenSSH. <a href="./rfc4255">RFC 4255</a> [<a href="./rfc4255" title=""Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints"">RFC4255</a>]
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 [<a href="#ref-Ed25519" title=""High-Speed High-Security Signatures"">Ed25519</a>].
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Ed25519 Public Key with SHA-256 Fingerprint</span>
The encoding of Ed25519 public keys is described in [<a href="#ref-Ed25519" title=""High-Speed High-Security Signatures"">Ed25519</a>]. 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 [<a href="#ref-FIPS180-4" title=""Secure Hash Standard (SHS)"">FIPS180-4</a>] 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.
<span class="grey">Moonesamy Informational [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc7479">RFC 7479</a> Using Ed25519 in SSHFP RRs March 2015</span>
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. Security Considerations</span>
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 <a href="./rfc4255">RFC 4255</a> [<a href="./rfc4255" title=""Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints"">RFC4255</a>] for a discussion of the security
considerations.
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. IANA Considerations</span>
IANA has added the following entry to the "SSHFP RR Types for public
key algorithms" registry:
+--------+-------------+------------+
| Value | Description | Reference |
+--------+-------------+------------+
| 4 | Ed25519 | [<a href="./rfc7479">RFC7479</a>] |
+--------+-------------+------------+
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. References</span>
<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>. Normative References</span>
[<a id="ref-Ed25519">Ed25519</a>] 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.
[<a id="ref-RFC4255">RFC4255</a>] Schlyter, J. and W. Griffin, "Using DNS to Securely
Publish Secure Shell (SSH) Key Fingerprints", <a href="./rfc4255">RFC 4255</a>,
January 2006, <<a href="http://www.rfc-editor.org/info/rfc4255">http://www.rfc-editor.org/info/rfc4255</a>>.
<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>. Informative References</span>
[<a id="ref-FIPS180-4">FIPS180-4</a>] National Institute of Standards and Technology, "Secure
Hash Standard (SHS)", FIPS PUB 180-4, March 2012,
<<a href="http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf">http://csrc.nist.gov/publications/fips/fips180-4/</a>
<a href="http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf">fips-180-4.pdf</a>>.
<span class="grey">Moonesamy Informational [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc7479">RFC 7479</a> Using Ed25519 in SSHFP RRs March 2015</span>
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]
</pre>
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