Re: [Sip-security] RE: SIP authentication problem when using RES in Digest-AKA

Greg Rose wrote in response to James Undery:

>> The RES 'secret' is surely going to be recalculated each time the
>> session entropy (i.e. nonce) changes. Thus I'd modify step 4 and add
>> pre7
> 
> This is definitely not in line with the intent of AKA, or the existing 
> architecture.

What I understood James proposing is that *if* AKA is used for the
authentication of an INVITE to the home after being used for authenticating
a REGISTER, then AKA should be re-run.

In the above, do you mean the 3GPP architecture in 'the existing architecture'?
 From what I understand the 3GPP architecture only intends to authenticate REGISTERs
with AKA. Therefore, if draft-niemi allows anything to happen after the
first authentication, it is beyond the 3GPP architecture. If plugging a
security hole requires that we never allow AKA authentication to be reused
and always need a new full AKA run, I would say that's fine. Greg, does
preventing reuse of the same RES help to block the security problem?
Also, I have proposed simply requiring 128 bit RES values to be used,
that solves the problem but is there any reason why we couldn't require
it?

Then we have another matter of how the INVITEs are authenticated in 3GPP.
That is based on the session keys generated as a side effect of AKA.
Let's keep the AKA re-run to the home -discussion separate from this.

Jari

_______________________________________________
Sip-security mailing list
Sip-security@ietf.org
https://www1.ietf.org/mailman/listinfo/sip-security