| Network Working Group | O.S. Sury |
| Internet-Draft | CZ.NIC |
| Updates: 4255 (if approved) | November 23, 2011 |
| Intended status: Standards Track | |
| Expires: May 26, 2012 |
Use of SHA-256 Algorithm with RSA, DSA and ECDSA in SSHFP Resource Records
draft-os-ietf-sshfp-ecdsa-sha2-01
This document defines how to store Secure Shell (SSH) ECDSA public keys and SHA-256 fingerprints in SSHFP Resource Records.
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The Domain Name System (DNS) is the global, hierarchical distributed database for Internet Naming. The Secure Shell (SSH) is a protocol for secure remote login and other secure network services over an insecure network. RFC 4253 [RFC4253] defines Public Key Algorithms for the Secure Shell server public keys.
The DNS has been extended to store fingerprints in a DNS recource record named SSHFP [RFC4255], which provide out-of-band verification by looking up a fingerprint of the server public key in the DNS [RFC1034], [RFC1035] and using DNSSEC [RFC4033], [RFC4034], [RFC4035] to verify the lookup.
RFC 4255 [RFC4255] describes how to store SSH public keys in SSHFP resource records and specifies a list of cryptographic algorithms to use for Algorithm Number and Fingerprint Type. This document extendes the SSHFP Algorithm Number list with the ECDSA algorithm [RFC6090] which has been added to Secure Shell Public Key list in RFC 5656 [RFC5656] and the SSHFP Fingerprint Type list with SHA-256 algorithm.
Familiarity with DNSSEC, SSH Protocol [RFC4251], [RFC4253], [RFC4250], SSHFP [RFC4255], and the SHA-2 [FIPS.180-3.2008] family of algorithms is assumed in this document.
This document updates RFC 4255 [RFC4255].
The format of the SSHFP RR can be found in RFC 4255 [RFC4255].
The fingerprint type octet describes the message-digest algorithm used to calculate the fingerprint of the public key.
SHA-256 fingerprints of the public keys are stored in SSHFP Resource Record with the fingerprint type 2.
The SSHFP Resource Record algorithm number octet describes the algorithm of the public key.
ECDSA public keys are stored in SSHFP Resource Records with the algorithm number 3.
ECDSA public key fingerprints MUST use SHA-256 algorithm fingerprint.
SSHFP-aware Secure Shell implementations SHOULD support the SHA-256 fingerprints for verification of the public key. Secure Shell implementations which support SHA-256 fingerprints MUST prefer the SHA-256 fingerprints if available over SHA-1 to prevent downgrade attacks.
SSHFP-aware Secure Shell implementations which also implement ECDSA algorithm for the public key SHOULD support SSHFP fingerprints for ECDSA public keys.
Given a private key with the following value in OpenSSH format:
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
The SSHFP Resource Record for this key would be:
server.example.net IN SSHFP 1 1 dd465c09cfa51fb45020cc83316fff21
b9ec74ac
The SSHFP Resource Record for this key would be:
server.example.net IN SSHFP 1 2 b049f950d1397b8fee6a61e4d14a9acd
c4721e084eff5460bbed80cfaa2ce2cb
Given a private key with the following value in OpenSSH format:
-----BEGIN DSA PRIVATE KEY-----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-----END DSA PRIVATE KEY-----
The SSHFP Resource Record for this key would be:
server.example.net IN SSHFP 2 1 3b6ba6110f5ffcd29469fc1ec2ee25d6
1718badd
The SSHFP Resource Record for this key would be:
server.example.net IN SSHFP 2 2 f9b8a6a460639306f1b38910456a6ae1
018a253c47ecec12db77d7a0878b4d83
Given a private key with the following value in OpenSSH format:
-----BEGIN EC PRIVATE KEY-----
MHcCAQEEINFBNyh3bKEQ4CQ7MfNgbEGINuRHjaIBrZkiWbaGPCZZoAoGCCqGSM49
AwEHoUQDQgAEAP70I5SJftZiBy8g50jz52N2gUNVRPE2tyiDyxJh1sjN4b5th2yy
y9zLL+dF9WFcLlAEKTwhOGqzsPj+UXFfmA==
-----END EC PRIVATE KEY-----
The SSHFP Resource Record for this key would be:
server.example.net IN SSHFP 3 2 821eb6c1c98d9cc827ab7f456304c0f1
4785b7008d9e8646a8519de80849afc7
This document updates the IANA registry "SSHFP RR Types for public key algorithms" and "SSHFP RR types for fingerprint types" [SSHFPVALS].
The following entries are added to the "SSHFP RR Types for public key algorithms" registry:
| Value | Description | Reference |
|---|---|---|
| 3 | ECDSA | [This doc] |
The following entries are added to the "SSHFP RR types for fingerprint types" registry:
| Value | Description | Reference |
|---|---|---|
| 2 | SHA-256 | [This doc] |
Please see the security considerations in [RFC4255] for SSHFP record and [RFC5656] for ECDSA algorithm.
Users of SSHFP are encouraged to deploy SHA-256 as soon as software implementations allow for it. SHA-2 family of algorithms is widely believed to be more resilient to attack than SHA-1, and confidence in SHA-1's strength is being eroded by recently announced attacks. Regardless of whether or not the attacks on SHA-1 will affect SSHFP, it is believed (at the time of this writing) that SHA-256 is the better choice for use in SSHFP records.
SHA-256 is considered sufficiently strong for the immediate future, but predictions about future development in cryptography and cryptanalysis are beyond the scope of this document.