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

[Antonin Décimo <[e-mail]>]

> > 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...

That also seemed off to me. To be fair regarding babeld, the "old"
hmac branch used 16-bytes blake2s, and my rewrite uses 32-bytes. We’re
using the reference blake2s implementation, and I changed 16 to the
provided BLAKE2S_OUTBYTES = 32 constant.

> 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".

Me too. I an exchange earlier this year, Donald and Juliusz explained
to me that the size of the output hash is considered part of the
hashing algorithm, so yes, I support making that explicit for blake2s.


-- Antonin