Re: Issue 27: Security and path testing (was: Comments on draft-ietf-mobike-protocol-00.txt)

 
- An attacker can "manufacture" a path test response (if it sees
  the corresponding request): I don't think this is a problem
  either. If the attacker has a working path to the responder, it
  could just forward the packet, and let the response come back
  without manufacturing anything.  And the path test message is
  not used as a substitute for dead peer detection anyway, so if
  the peer is really dead, an attacker can't hide that.

mohanp> This is the one i  was mainly concerned with. DPD is
mohanp> done only for the already working path. If we need
mohanp> to know whether an alternate path (.e.g cheaper path)
mohanp> works or not, we need to send PATH_TEST message
mohanp> If you get a false response e.g. when it
mohanp> is not working, attacker sending a response back can cause
mohanp> a failover unncessarily. Yes, DPD now can now
mohanp> detect this and fail back to the other path. But the
mohanp> other path (which was working and still working) can be 
mohanp> "failed" by the attacker by sending a false response.
mohanp> I think this is undesirable. So, i see the PATH_TEST message
mohanp> as DPD but sent with different address pair. 

And encrypting and integrity protecting these messages is not as
easy as it sounds. For instance, if the response message is
lost, and the initiator retransmits the same request, does the
new response have to be identical to the previous one?  (For
normal IKEv2 messages, the answer is yes. But this implies
keeping state in the responder, with window mechanism to limit
the amount of state that needs to be kept. If the answer would
be yes for path test messages as well, how many path test
messages would have to be kept?)

mohanp> Why do we need to keep state on the responder for
mohanp> sending back same response to a PATH_TEST message?  
mohanp>  The response is an empty message back to the addresses
mohanp> where it came from. NAT-detection is also stateless.
mohanp> So, i am missing something here..

-mohan


But perhaps there's some angle I haven't thought about yet;
more comments are welcome...

Best regards,
Pasi