tree 189387b1723bfd19136e6450bb0a9fa78038b5ef
parent 4f68b04018a35fe6aff4298565cdfc1f0c781809
author Hanno Becker <hanno.becker@arm.com> 1526919402 +0100
committer Hanno Becker <hanno.becker@arm.com> 1565625903 +0100

Restructure incoming CliKeyExch: Add frame for restructuring

This commit adds declarations and dummy implementations for
the restructured incoming client key exchange handling that
will replace the previous ssl_parse_client_key_exchange().

The entry point for the CliKeyExchange handling that is called
from the handshake state machine is

   `ssl_process_client_key_exchange()`,

splitting the processing into the following steps:

- Fetching: Read next message from the messaging layer
            and check that it has the correct type.
            The ClientKeyExchange message is never
            omitted, so there is no ambiguity in what
            to expect, and hence no dedicated preparation
            step as for other handshake states.
- Parsing:  Parse the ClientKeyExchange message and
            use the information in it to derive keying
            material such as the shared (EC)DHE secret.
- Postprocessing:
            Compute the session keys from the available
            keying material. This splits in two steps:
            (1) Build the PreMasterSecret (PMS) from the
                available keying material, e.g. concatenate
                the (EC)DHE secret with a PSK, if used.
            (2) Extract the MasterSecret and Session Keys
                from the PreMasterSecret.

The subsequent commits will scatter the code from the previous
monolithic function ssl_parse_client_key_exchange() among those
dedicated functions, commenting out each part of
ssl_parse_client_key_exchange() that has already been dealt with.
This gradual progression is meant to ease reviewing. Once all
code has been moved and all changes explained,
ssl_parse_client_key_exchange() will be removed.