[IPsec] Ticket-by-reference and protecting the exchange

Tough chairs! Here's the answer I was going to say at the 
microphone:

The client does not (and cannot) know whether it's using
"ticket-by-value" (where the ticket contains the gateway's state, 
in encrypted form) or "ticket-by-reference" (where the ticket contains
only a pointer to state stored locally by the gateway), or even a
combination (some state is in the ticket, some is stored locally).

In *addition* to storing the ticket blob, the client has to store the
keys from the old IKE_SA (and this is done even if ticket-by-reference
is used -- since the client cannot know that). The client uses these 
keys to protect the resumption exchange. The gateway also needs these 
keys; it gets them from the ticket, or from its local storage (using 
the ticket as a pointer).

If the gateway is using ticket-by-reference, and there's a cluster of
multiple gateways, the cluster members need to communicate somehow
(and obviously this communication needs to be secured somehow).
This protocol is explicitly beyond the scope of the charter.

(BTW, if the gateway uses ticket-by-reference, things work 
pretty much the same way as draft-xu-ike-sa-sync, except that 
the terminology is slightly different, and this document doesn't
say anything about how multiple gateways communicate, possibly
via some database server, called "stub bank" in draft-xu-...).

Best regards,
Pasi
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