generate new ClientHello.random for HelloRetryRequest (for issue #185)

[davegarrett]

PR to add a simple requirement that retried ClientHello messages must not reuse random values and servers must check for and reject them if they do. (suggested by Karthik)

[ekr]

I think it's an open issue whether we should require a new ClientRandom, but requiring that the server check for it is harmful because it makes it impossible to do a stateless HelloRetryRequest.

[davegarrett]

Ok, then should I downgrade it to a SHOULD (or MAY) or drop the check requirement completely? I don't have a strong objection to dropping it.

On Friday, June 19, 2015 11:52:07 pm ekr wrote:

I think it's an open issue whether we should require a new ClientRandom, but requiring that the server check for it is harmful because it makes it impossible to do a stateless HelloRetryRequest.

[davegarrett]

Also, would that also require the session hash to completely restart on the new ClientHello and discard the previous messages? (see also issue #104) I added in clarification for that before noticing your comment, so that may need changing as well.

[martinthomson]

Weeeelll, if we include a cookie, it is possible to check statelessly. But the cookie might get a little big :)

[davegarrett]

I've revised this to drop the required check. (also now based on current master, as it was rather bitrotted)

[ekr]

I don't think we want this.