[TLS] A crazy idea

[Michael D'Errico <[e-mail]>]

Here's a crazy idea: we could define a completely incompatible change
to the way Finished messages are calculated even on initial handshakes.

A client can initially try connecting using the new Finished message
calculation, and if that fails, fall back to the original (if it's
willing to risk talking to an unpatched server).

The server has the advantage of receiving the client's Finished message
before it needs to send its own, so it can compute both the new and the
old versions to see which the client supports.  Then it can decide
whether to continue with the handshake or abort.  This also thwarts any
tampering by a MITM since neither calculation would match if messages
were altered.

For session resumption, each side would need to remember whether the
new or the old Finished calculation was used.

Just throwing the idea out there....

Mike