RE: Sub/Not Security, Presence service identifiers

>   http://www.imppwg.org/ml-archive/IMPP-WG/200208/msg00003.html
>
> The purpose of the example is to demonstrate a situation in which it
> is important that a presence service has an identifier that
> distinguishes it as a presences service.  In that example, a bad guy
> that is not approved to behave as a presence service, is fabricating
> presence information in an effort to spoof a watcher into using the
> wrong inbox for instant messaging.  Since the bad guy is creating
> presence information and signing it, timestamping will not foil this
> attack.

I guess I'm a little confused, then. In a previous message, I think with
respect to the same example, you wrote

"Signing the presence information by the person that created it does
not fix the problem, because a spoofing presence service could collect
signed presence information and replay them in an order that
misinforms the watcher."

I don't understand how this style of replay attack is viable if the presence
information signed by the creating principal includes a timestamp covered by
the signature.

Could you clarify whether you are concerned about a replay attack or some
other form of attack, and which parts of the system have to be subverted for
that attack to succeed?  It would be helpful to me, at least, for you to be
very explicit about these points because some things that may be obvious to
you are not obvious to me.

--Mark





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