Subject: [Sip] Questions to draft-undery-sip-auth-00.txt

From: "Steffen Fries" <[email-masked]>
Date: Thu, 21 Feb 2002 09:43:12 +0100

James,

I just went through the extensions to HTTP Digest 
Authentication. I've got some questions to draft-undery-sip-
auth-00.txt:

1. How does the nextnonce mechanism deal with packet loss? It
   might be that a response to a UA gets lost when using UDP.
   When the UA sends the next request, which nonce will be used
   here? The nextnonce sent in the last respone the UA   
   received? How is a proxy supposed to react in this case?
2. Does this scheme require a call stateful proxy storing
   nonces and nextnonces for a certain time?

Regards
	Steffen

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---

From: "James Undery" <[email-masked]>
Date: Thu, 21 Feb 2002 09:26:49 -0000

> -----Original Message-----
> From: Steffen Fries [mailto:[email-masked]]
 
>    received? How is a proxy supposed to react in this case?

The nextnonce mechanism deals with packet loss by being carried in SIP.
The standard SIP retransmission mechanism cover this. The UA MAY cache
nonces however it likes although SHOULD follow the guidelines in the
bis. If a UA is within a dialog I'd hope it used the freshest nonce it
had, i.e. nextnonce if that was provided. How the proxy deals with
nonces is really a matter of local policy.

I.e. On receiving and challanging a REGISTER the registrar may wish to
store the nextnonce allowing one time long duration nonces. A generic
proxy may want stateless behaviour where nonces are generated with a
secret only it knows and time limited or tied to a dialog.

>    nonces and nextnonces for a certain time?

Definately not, the possible implementation in section 6.1 demonstrates
a nonce that need not be stored and can be verfied as fresh. The format
even allows preliminary checking of the freshness without preforming a
hash.

James