Re: Presence service identifiers

[email protected] (John D. Ramsdell) writes:

> * Given a PRES URI that names a presentity, a client should be able to
>   construct the presence service principal that provides subscription
>   service for the presentity.
> 
> The last point is necessary so that a client can be sure the proper
> presence service is providing notifications, and in particular,
> determine that an unauthorized person is not providing presence
> service.

Here is a scenario that motivates this point.  Suppose you know my
presentity is available at pres:[email protected].  You subscribe to
it by doing a DNS lookup of mitre.org and say the APEX protocol to get
a port and an Internet Protocol address of the presence service
providing my presentity.  Because the request was routed through a
subverted host, you receive two signed notifications back immediately,
one that looks like:

         Content-type: Message/CPIM
 
         To: pres:user@host
         From: pres:[email protected]
         Datetime: 2002-07-18T13:38:22-8:00
 
         Content-type: application/cpim-pdif+xml	
 
         <presence entity='pres:[email protected]>
           <tuple id='im'>
             <status><basic>open</basic></status>
             <contact>im:[email protected]</contact>
           </tuple>
         </presence>

and the other one looks like:

         Content-type: Message/CPIM
 
         To: pres:user@host
         From: pres:[email protected]
         Datetime: 2002-07-18T13:37:29-8:00
 
         Content-type: application/cpim-pdif+xml	
 
         <presence entity='pres:[email protected]>
           <tuple id='im'>
             <status><basic>open</basic></status>
             <contact>im:ramsdell@badhost</contact>
           </tuple>
         </presence>

Both notifications are signed and include a certificate with the
presence URI in the 'From' header in its Subject Alternative Names.
Which instant inbox are you going to use?

John



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