Re: [TLS] [kitten] RFC 5929 tls-unique clarification?

[Martin Rex <[e-mail]>]

Simon Josefsson wrote:
> 
> I'm implementing an API for RFC 5929 in GnuTLS and I'm having some
> troubles with the specification.  Section 3.1 says:
> 
>    Description: The first TLS Finished message sent (note: the Finished
>    struct, not the TLS record layer message containing it) in the most
>    recent TLS handshake of the TLS connection being bound to (note: TLS
>    connection, not session, so that the channel binding is specific to
>    each connection regardless of whether session resumption is used).

I've also started adding code for tls-unique channel bindings and
now I'm also wondering about this description:

rfc5929 says

"(note: the Finished struct, not the TLS record layer message containing it)"

which, according to rfc-5246 looks like this:

http://tools.ietf.org/html/rfc5246#section-7.4.9

   Structure of this message:

      struct {
          opaque verify_data[verify_data_length];
      } Finished;

      verify_data
         PRF(master_secret, finished_label, Hash(handshake_messages))
            [0..verify_data_length-1];


What puzzles me now:

rfc5929 clearly says "Finished struct", which differs from the
verify_data as used by rfc5246 (TLS extension RI) in that
it WILL include the length field of the verify_data opaque vector.

If there had been any mentioning of the CB sizes for tls-unique, similar
to rfc5746 (12 octets for TLSv1.x and existing cipher suites,
36 octets for SSLv3), then I would not be wondering whether this
spec really means what it says.

What size does your tls-unique CB have for TLSv1.x?  12 or 13 octets?

-Martin