enable DTLS negotiation

[Nikos Mavrogiannopoulos]

On Sat, 2016-09-17 at 08:50 +0000, David Woodhouse wrote:
> > opaque psk_identity<1..2^16-1>;
> > psk_identity identity_list<1..2^16-1>;
> > 
> > That means that for id 'psk' you have:
> > 
> > > 
> > > uint16(size of psk + 2)||uint16(size of psk)||psk|
> > or |uint16(5)||uint16(3)||psk|
> >       2-bytes  2-bytes    3-bytes
> > 
> > Where the uint16 is in big-endian order.
> More generally, since the client can propose multiple identities, it
> is...
> 
>   uint16 10015 // provisional extension ID
>   uint16 extlen // all extensions have a length of their payload

These you shouldn't normally care about (at least in the gnutls api if
I remember well)

> ... then the payload contains what you talked about above...
>   uint16 entirely_redundant_payload_len_again == extlen-2
>     uint16 ident1_len
>     char "dave"
>     uint16 ident2-len
>     char "nikos"
>     ...

right.

> Can we ditch the first in uint16 in payload, given that it is
> entirely
> redundant? Or am I misreading the spec to put it there in the first
> place,
> and the formal language is supposed to *include* what I called
> 'extlen'

According to the protocol tt has to be there.