[PATCH 0/4] Add MAC authentication support to the Babel protocol

[Ondrej Zajicek]

On Tue, Feb 25, 2020 at 07:30:46PM +0100, Toke Høiland-Jørgensen wrote:
> Ondrej Zajicek <santiago at crfreenet.org> writes:
> > For blake2s_bird_init(), IMHO it should behave like other keyed-hash,
> > i.e. pad with zeroes (for shorter) or ignore rest (for longer).
> >
> > Perhaps we should have some hook or flag in MAC auth description
> > structure that is used to validate keys based on used algorithm (so it
> > would warn for bad-length keys for Blake2, but only for short keys for
> > HMAC based ones.
> 
> The Blake2 implementation already 0-pads short keys. But I'm not sure if
> it's a good idea to allow that; even if it's zero-padded it's still a
> low amount of entropy, no?

Yes, but such validation should be in independent function, applied
during config-parse time. Functions computing MAC (including *_init())
should just handle any key length to avoid corner cases and failures
there.


> > It seems to me that in order to handle Blake2s MACs (and other MACs that
> > require entropy-dense keys), the proper solution is to have a option to
> > specify a key in some form of binary-to-text encoding (e.g. hexadecimal):
> >
> >   password 70:61:73:73:77:64
> >
> > instead of:
> >
> >   password "passwd"
> 
> Yes, I think this is a good idea (or, well, we could allow both).

Yes, there should be both.

> Should we use the colon-separated format, or a straight hex string for easy
> copy-paste to babeld? E.g.,
> 
> password 0x7465737474657374746573747465737474657374746573747465737474657374

I have no strong preference for specific format (but i would prefer
hexadecimal based formats over Base64 / Base58 based ones).

I think it is useful to have some separators (space, colon, or dash), but
perhaps it could be optional.

Also note that the key is not a number, but a byte sequence - initial
zeroes are significant. So perhaps it should be a different token (and
there is no reason for 0x).

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."