[babel] Minor clarification to HMAC

[Juliusz Chroboczek <[e-mail]>]

Dear all,

Sawssen and Étienne (in copy of this mail) are currently working on
cleaning up and completing the reference implementation of draft-...-hmac.
We have just realised that the draft is not quite clear on two points.

The draft says that a neighbour entry MUST NOT be created before HMAC is
verified (Section 4.3 first bullet).

It later says that a neighbour entry "might need to be created" when
a challenge is sent, and "may need to be created" when a challenge is
received.  However, it does not say whether it is legal to create an entry
earlier.

I would therefore like to kindly request the permission of the group and
the chairs to add the following between the first and second bullet points
of Section 4.3:

  * A neighbour entry for the sender of the packet MAY be created at this
    stage.  (Alternatively, an implementation MAY delay the creation of
    a neighbour entry until a challenge request or reply is received.)

This clarification does not invalidate any implementations, it just makes
the intent of the draft authors more explicit.

-- Juliusz