Internet Engineering Task Force (IETF) S. Moonesamy Request for Comments: 7479 March 2015 Category: Informational ISSN: 2070-1721
Using Ed25519 in SSHFP Resource Records
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.
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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].
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:
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.
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.
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