Re: : FW: IPSec use with Diameter (from the IPSEC WG list)

Bernard Aboba wrote:

> Without a protocol binding in phase 1, there isn't a way for the responder
> to know what the SA is being brought up for.  Therefore it has no way to
> tell the initiator what certs it will accept.  It can give the initiator
> the union of all possible trust anchors, but then it once phase 2
> completes, it is possible that the responder will learn that the initiator
> chose the wrong certificate.  This isn't fixed in 2401bis, because it's
> an inherent problem with IKEv1.

Theoretically, the initiator can be guided by configuration to choose
the right certificate for the purpose that the phase 1 is being brought
up for. This works as long as the responder is willing to accept any of
the trust anchors. At the time phase 2 is being brought up, an
authorization decision can determine whether the initiator did the
right thing.

But this is very brittle, does not involve any explicit communication
over the protocols, and relies on correct configuration and knowledge
about what the other side expects. As a result it may not be very easy,
particularly in an inter-domain case.

--Jari