RE: [Sip] SIP Identity using Media Path

["Dan Wing" <dwing@xxxxxxxxx>]

> An SBC can modify almost any header.

Yes.

> Looking at chapter 4.1, 
> I would say that at least the To- and From headers are in 
> the "risk zone" (EVEN if you only use the addr-spec part).

If the From header is modified, the identity is broken 
anyway.  Such modifications of the From header are discussed
in the Background section of draft-wing-sip-identity-media-00.

Allowing modifications of the To header creates the 
opportunity for an attacker to launch a replay attack by
substituting the To address and replaying the message 
until the Date: header is old enough that receiving 
authentication servers reject the Date: header out of 
hand.

> The CSeq (at least the digit portion) may also be modified, 
> for example if there has been some "dialog piggybacked" requests 
> sent between the SBC and another entity, but not end-to-end. In 
> that case the the SBC may have to increase the CSeq before 
> forwarding the request, if the digit portion value has already 
> been used in a request sent by the SBC in the same direction.

That seems like a good opportunity, within that trust domain 
between the SBC and the other entity, to use 
P-Asserted-Identity.

-d