Re: : issue with expected response calculation

Replying on my own question ...

On 4/12/05, Jo Hermans <[email protected]> wrote:
> 
> I have a problem with paragraph 8.5.6.1 <http://8.5.6.1> in 
> draft-ietf-aaa-diameter-sip-app-07 , 3th paragraph ("Please note that the 
> expected response ...")
> 
> The draft mentions that the expected response calculation can't be done 
> when the SIP UA has sent a expected response based on client nonces. It then 
> mentions that this is the case when the qop-parameter is present in the 
> client request.
> 
> That last part I don't understand. I though that H(A1) is dependent on the 
> algorithm, not qop. Qop has only influence on the A2 and digest, which are 
> both calculated in the Diameter Client (SIP Server). See also <
> http://danforsberg.info:8080/draft-ietf-aaa-diameter-sip/issue40>
> 
> But even then I don't understand. I think that the Diameter Server does 
> has the client-nonces available (they're in the SIP-Authorization AVP, and 
> were used to calculate the request digest !)), and is able to calculate a 
> H(A1). Even if MD5-sess was used, it could still calculate H(A1). MD5-sess 
> also has the added advantage that H(A1) could only be used once, which is 
> also the reason why draft-sterman-aaa-sip-04.txt doesn't want to use MD5 
> unless the message is protected against eavesdropping.


Now I see that the Digest-HA1 attribute is present in the SIp-Authenticate 
AVP, which probably never saw a cnonce at all, because it's part of the 
challenge. My mistake was that I thought that it was in SIP-Authorisation 
too.

This also means that if a server decides to include Digest-Ha1 to assist the 
SIP-server (to avoid that the next packet with the Sip-Authorisation should 
be forwarded to the server too), then it should not offer the SIP UA to use 
MD5-sess, because that includes client-nonces in A1. Qop is not a problem, 
despite paragraph 3 in section 8.5.6.1 <http://8.5.6.1> of sip-app-07.

I agree that if qop is missing and algorithm is MD5, client-nonces aren't 
> used at all (backwards compatibility with RFC2069). H(A1) might be stored 
> inside the Diameter Client (SIP server) when it's first received, and reused 
> later on. Is it this that the draft is alluding to ?
> 
> -- 
> Jo Hermans
> 
> "Eagles may soar, but weasels aren't sucked into jet engines" 




-- 
Jo Hermans
www.bluesweb.org <http://www.bluesweb.org>

"Eagles may soar, but weasels aren't sucked into jet engines"