Subject: [Sip] draft-cao-sip-response-auth-00

From: "James M. Polk" <[email-masked]>
Date: Sun, 31 Jul 2005 15:56:30 -0500

Interesting idea, and I have a few comments:

section 3.1 needs to number the requirements for clarity sake

section 3.1 seems to be saying that the UAC shouldn't trust the UAS (it 
just contacted with a Request message, BTW) until the UAC has confirmed the 
UAS is really the UAS it contacted.

Kinda a "before we can speak, I need to know you are you who you say you 
are without you speaking (because that would be an unchecked reply)."

seems like a bit of catch-22, or am I missing something?

In the example in section 3.1, why should Alice trust Proxy2? She has zero 
prior association with that proxy because all communication to Bob has gone 
through Proxy1, has it not?

 From how you've written this, if there are 10 proxies between proxy1 and 
proxy2, only proxy2 will send this responder verification 183 message, right?

Wanting to know if Alice is going to receive a 183 per SIP hop her Request 
traverses?

The 183 mentioned in secgtion 3.1 is absent from the flow example in 
section 3.2. Why?

The flow on page 7 should be labeled.

But, within that flow, say there are 10 SIP Hops between proxy1 and proxy2, 
is this ID suggesting there needs to be a SUB/NOT exchange between proxy1 
and proxy2 anyway? If so, how would proxy1 learn about proxy2?

What if there were/is a B2BUA in between proxy1 and proxy2?

This example message flow needs to address a more complex scenario or two 
to learn how this proposal reacts. May I suggest both:

alice <=> proxy1 <=> proxy3 <=> proxy4 <=> proxy2 <=> Bob

and

alice <=> proxy1 <=> proxy3 <=> b2bua1 <=> proxy4 <=> proxy2 <=> Bob

  to tease this proposal out?

The 3rd paragraph talks about a 180 being the first time Biloxi Proxy needs 
to do "real" work, and this 180 was left out of the section 3.2 example. Why?

Last paragraph on page 8
"UAC may receive the response code 431 Failed Responder Identity.  UAC 
should choose to avoid the verification of the responder identity. UAC 
should treat it as a failure and may terminate the dialog."

How is this done? With a normal ACK then a BYE? Wouldn't this give more 
information to this bad-guy proxy?

section 6.1 - the Responder header is to give the first hop proxy (in the 
response direction) the address of the responder, just like the To: field? 
Is this level of redundancy necessary since Bob MUST have a shared secret 
between his UA and the Biloxi proxy2 server (as stated previously)?

The Security Considerations section reads like a summary section advocating 
the doc, rather than a "if implemented badly, these are the bad results" 
type of text.

cheers,
James

                                 *******************
                 Truth is not to be argued... it is to be presented.

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