Both Diffie-Hellman (DH) and Key Encapsulation Mechanism (KEM) based
key exchange methods use a common ke_test_vector format. The
set_seed() function is used to provide deterministic private key
material for the crypto tests.
This way we can use the IKE_REKEYED state for both redundant and old SAs
to suppress ike_updown().
In the ike-delete task we don't suppress events in state IKE_REKEYING as
that's the case when we delete an SA the peer is currently rekeying with
multiple key exchanges.
This gives us more flexibility with tasks that return NEED_MORE (currently
none of the colliding tasks do, but that will change with multi-KE
rekeyings). The active task has to check itself if the passive task is
done and should be removed from the task manager.
Since f67199378df9 ("ike-rekey: Handle undetected collisions also if
delete is delayed") we only ever track tasks of type TASK_IKE_REKEY, so
there is no need to check the type or use the generic task_t interface.
Also changed some of the comments to clarify collision handling.
If the peer successfully rekeyed the SA it gets marked as IKE_REKEYED
and it remains until the peer deletes it (or a timeout). There is no
point in rekeying such SAs again.
IKE_REKEYING will be relevant if we have multi-KE rekeyings and are
waiting for followup key exchanges for a passive rekeying.
Initially, this is handled with a key derivation for each
IKE_INTERMEDIATE exchange. When rekeying the keys are derived only when
all IKE_FOLLOWUP_KE exchanges are done.
We avoid parsing messages with unexpected message IDs. This allows us to
process and detect retransmits of messages for which we don't have the keys
anymore (i.e. IKE_INTERMEDIATE after IKE_SA_INIT and changing the keys).
This also changes how retransmits for fragmented messages are triggered,
previously we waited for all fragments and reconstructed the message
before retransmitting the response. Now we only track the first
fragment and if we receive a retransmit of it respond immediately
without waiting for other fragments (which are now ignored). This is in
compliance with RFC 7383, section 2.6.1.
