[babel] Information model and YANG: about HMAC

[Juliusz Chroboczek <[e-mail]>]

My comment during the meeting, expanded.

HMAC does not carry keys or algorithm identifiers on the wire: algorithm
and key are provisioned by means outside of the Babel protocol (currently
a configuration file, but we're working on implementing key rotation at
runtime), then only the results of the HMAC computation are sent on the
wire.

Hence, the base protocol does not need a registry of HMAC algorithm
identifiers: the only place where HMAC algorithms appear is the config
file, and how they are expressed there is purely a local implementation
decision.

What the information model and YANG do is, among other things, to export
the configuration in an interoperable format.  Hence, if we need to export
the HMAC keys, we'll need a registry of HMAC protocols.

If we do, then the initial value should probably be just one entry:
HMAC-SHA256.

-- Juliusz