[openpgp] WWhy or why not SHA{2,3}-512 (was: SHA3 algorithm ids)

Werner Koch <wk@gnupg.org> Tue, 11 August 2015 15:50 UTC

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From: Werner Koch <wk@gnupg.org>
To: Peter Gutmann <pgut001@cs.auckland.ac.nz>
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Date: Tue, 11 Aug 2015 17:47:54 +0200
In-Reply-To: <9A043F3CF02CD34C8E74AC1594475C73F4AD7C72@uxcn10-5.UoA.auckland.ac.nz> (Peter Gutmann's message of "Tue, 11 Aug 2015 13:21:07 +0000")
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Subject: [openpgp] WWhy or why not SHA{2,3}-512 (was: SHA3 algorithm ids)
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On Tue, 11 Aug 2015 15:21, pgut001@cs.auckland.ac.nz said:

> What's the clear need for -512?  By which I mean a demonstrated practical need
> for a hash size of 64 bytes, not a hypothesised need given an imaginary
> attack.  I can see a need for SHA-256 (to replace SHA-1), but for something
> like SHA3-512 all I can see are downsides (compared to SHA2-256).

One advantage of SHA-512 (SHA2) is that it faster than SHA-256 on modern
machines.  Thus SHA-512 truncated to 256 might be an option.  This would
eventually allow to write a small application which uses SHA-512 as its
only hash algorithm.



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