Re: [TLS] New drafts: adding input to the TLS master secret

[Simon Josefsson <[e-mail]>]

I have read these two documents and believe they are generally fine.  As
far as I can tell, they are not backwards compatible with earlier
proposals.  But that is not important.

There is one thing in draft-hoffman-tls-additional-random-ext-00.txt
that bothers me: There is no requirement that additional random data is
generated using cryptographic principles.  This means the extension can
be used as a general-purpose extension mechanism to exchange data that
has meaning to, for example, some middle-ware that sits between the
client and server.

Is this the intention?  I'm assuming no, and that the
additional_random_value actually are intended to be, well, just an
additional random value.

Therefor, I would suggest that a new requirement is added:

   The client and server MUST generate the additional_random_value data
   using a secure random number generator.  [RANDOM] provides guidance
   on the generation of random values.
...
   [RANDOM]   Eastlake, D., 3rd, Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              June 2005.

This is similar to what's in RFC 5246 says about the random_bytes field:

7.4.1.2.  Client Hello
...
      random_bytes
         28 bytes generated by a secure random number generator.

/Simon