RE: On the need for presence service identifiers

At 12:17 PM 8/21/02 -0400, Mark Day wrote:
> > Eve subscribes to both Alice's and Bob's presentity and saves Sunday's
> > version of their presence information.  On Monday, either by playing
> > with DNS or by intercepting traffic between alice.com and bob.com, Eve
> > sends Bob's old presence information to Alice, and Alice's old
> > information to Bob.  Because of this, all day Monday, Alice and Bob
> > think each other is offline, and fail to communicate.  Alice and Bob
> > have no way of knowing that the presence information they have is
> > stale.  This attack is foiled if notification content is timestamped
> > and signed when a notification operation is invoked.
>
>I think I understand this, and agree that it is a potential vulnerability. I
>disagree about its likely practical importance and the proposed solution.

I tend to agree.  I think a far simpler way to achieve the same effect, and 
which is not repaired by the proposed security features, is for an attacker 
to simply block delivery of notification messages.

[Catching up on the debate -- this is just a point response to what I 
perceive as a point issue.]

#g

-------------------
Graham Klyne
<[email protected]>



  [reminder: [email protected] for non-technical discussions, please]