Re: [babel] Babel-MAC: Blake2s is 128-bits by default

Juliusz Chroboczek <jch@irif.fr> Fri, 06 November 2020 23:06 UTC

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Date: Sat, 07 Nov 2020 00:06:18 +0100
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From: Juliusz Chroboczek <jch@irif.fr>
To: Toke =?ISO-8859-1?Q?H=F8iland-J=F8rgensen?= <toke@toke.dk>
Cc: babel@ietf.org, Valery Smyslov <valery@smyslov.net>, Donald Eastlake <d3e3e3@gmail.com>, Barbara Stark <bs7652@att.com>
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Subject: Re: [babel] Babel-MAC: Blake2s is 128-bits by default
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> Okay, something seemed off about this when I read it just now, so I just
> double checked: And in fact both implementations use 32-byte Blake2s
> digest sizes...

Looking through the git history... the original version implemented by
Clara, Weronika and myself used 16-byte hashes, which was the original
intent, for the reasons outlined in my previous mail.

The version currently maintained by Antonin does indeed generate 32-byte
hashes.  While I haven't checked myself, Toke says that so does his
version, and the two versions have been shown to interoperate.

> I still support making the change and specifying the size, but to
> correspond to current implementation practice the change would need to
> be "with 256-bit (32 octet) hashes".

No strong opinion either way.  Let's give people a chance to comment.

-- Juliusz