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

Juliusz Chroboczek <jch@irif.fr> Thu, 26 November 2020 12:04 UTC

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Date: Thu, 26 Nov 2020 13:04:40 +0100
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From: Juliusz Chroboczek <jch@irif.fr>
To: Toke Høiland-Jørgensen <toke@toke.dk>
Cc: babel@ietf.org, Valery Smyslov <valery@smyslov.net>, babel-chairs@ietf.org
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Subject: Re: [babel] Babel-MAC: Blake2s is 128-bits by default
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>> I do not believe that it impacts the security in any way (2^128 ns is
>> roughly 10^12 times the age of the universe), but I could be wrong.

> Yeah, makes sense, let's keep it at 32 bytes :)

Excellent.  I'm therefore going to make the following change in AUTH48:

  - in Section 4.1, replace

   Every implementation MUST implement HMAC-SHA256 as defined in [RFC6234]
   and Section 2 of [RFC2104], SHOULD implement keyed BLAKE2s [RFC7693],
   and MAY implement other MAC algorithms.

   Every implementation MUST implement HMAC-SHA256 as defined in [RFC6234]
   and Section 2 of [RFC2104], SHOULD implement keyed BLAKE2s with 128-bit
   (16-octet) digests [RFC7693], and MAY implement other MAC algorithms.

I will not change the following text in Section 7:

    Ideally, they should have a length of 32 octets (both for HMAC-SHA256
    and Blake2s), and be chosen randomly.

Donald, are you willing to call consensus on this point?

-- Juliusz