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

[Toke Høiland-Jørgensen <[e-mail]>]

Juliusz Chroboczek <[e-mail]> writes:

> Dear all,
>
> We've had a discussion with Barbara and Toke today, and we've come to the
> conclusion that there is an oversight in draft-ietf-babel-hmac-12.  In
> Section 4.1, we say
>
>    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.
>
> As Valery Smyslov noted, BLAKE2s is able to produce hashes of any size
> between 1 and 32 octets (8 and 256 bits).  However, both implementations
> of Babel-MAC only ever produce 16-octet BLAKE2s hashes.

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...

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".

-Toke