[Babel-users] Reworked implementation of HMAC authentication

[Juliusz Chroboczek]

Hi,

I've finally gotten my act together, and reworked Clara's and Weronika's
implementation of Babel-HMAC.  You can get the code by doing

    git clone -b hmac --recurse-submodules https://github.com/jech/babeld

While this code is almost completely untested, it is meant to eventually
implement the protocol described in

    https://tools.ietf.org/html/draft-ietf-babel-hmac

Known issues:

  - no interop testing has been done yet;
  - we create a neighbour entry too early, which makes us vulnerable to DoS;
  - we compute HMAC for each TLV, rather than just once for the whole
    packet, which, again, makes us vulnerable to DoS;
  - we don't timeout neighbours properly, which makes us vulnerable to
    delayed packets;
  - we only support sending one HMAC (receiving multiple HMACs should
    work, but for obvious reasons it's untested);
  - we don't support key rotation.

You can test this code by saying something like:

    babeld -C 'key id test type sha256 value ebf49e6fbc6414aa567e30891846e96963cdda73289b9cd245d67ff9d281abc0' -C 'interface eth0 hmac test'

The "key" stanza defines a key of type sha256, with the value given as
a 32 byte-long hex key. The "interface" stanza enables the key on the
interface eth0.

In addition to "type sha256", we support "type blake2s", which requires
a 16 byte-long key.

-- Juliusz