Re: [Cfrg] Using ED25519 in SSHFP Resource Records - draft-moonesamy-sshfp-ed25519-01

Alyssa Rowan <akr@akr.io> Tue, 01 April 2014 18:01 UTC

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Date: Tue, 01 Apr 2014 19:01:51 +0100
From: Alyssa Rowan <akr@akr.io>
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Subject: Re: [Cfrg] Using ED25519 in SSHFP Resource Records - draft-moonesamy-sshfp-ed25519-01
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On 01/04/2014 17:32, S Moonesamy wrote:

> It would help if I could get some feedback from CFRG about 
> draft-moonesamy-sshfp-ed25519-01

Not much to review, really. I see no problems; straightforward.

OpenSSH has already adopted Ed25519 independently (as in
djb/Duif/Lange/Schwabe/Yang, with SHA-512 as the hash).

While I could suggest (and have suggested) a small improvement (simply
swapping the SHA-512 for a newer, better, faster hash, from the SHA-3
competition finalists: e.g. SHA-3?), and CFRG may document a slightly
more generalised version capable of working with stronger curves,
I have no actual worries in practice about Ed25519 as drafted.

The SHA-3 final round candidates are all technically better, but SHA-2
[despite its progenitors' murky reputation] is absolutely fine right
now as far as I know (except for length-extension, which isn't a real
issue here afaik).

There's no real need to get a 256-bit fingerprint from a 256-bit
public blob: you could just as well include the public key verbatim.
But given an SHA-256 hash has about the same strength as Ed25519, and
it's a fingerprint so matches existing practice with other SSHFP
records, it does no harm.

My only suggestion: prohibit using (weaker, deprecated) SHA-1
fingerprints with these newest (stronger) keys. [Just in case someone
mistakenly thinks it'd be a good idea.]

Other than that, as far as I'm concerned, stick a fork in it: it's
done, go ahead and get its public key RR type allocated.

- -- 
/akr
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Re: [Cfrg] Using ED25519 in SSHFP Resource Record… Alyssa Rowan
Re: [Cfrg] Using ED25519 in SSHFP Resource Record… S Moonesamy
Re: [Cfrg] Using ED25519 in SSHFP Resource Record… S Moonesamy
Re: [Cfrg] Using ED25519 in SSHFP Resource Record… Nico Williams
Re: [Cfrg] Using ED25519 in SSHFP Resource Record… Daniel Kahn Gillmor
Re: [Cfrg] Using ED25519 in SSHFP Resource Record… S Moonesamy