Subject: [SIP] Request/Responses from other addresses

From: "McMurry, Kathleen" <[email-masked]>
Date: Mon, 05 Jun 2000 18:52:39 +0000

What is the proper behavior of a Proxy in the following scenarios:

Scenario1:

OUA-----INVITE----->PS------INVITE----->TUA
OUA2-----CANCEL---->PS

In other words - the CANCEL comes from a different address than the original
INVITE came from.  The same question applies to a "retransmitted" INVITE
request prior to the final response.

Scenario2:

OUA---INVITE---->PS-----INVITE---->TUA
TUA2--->200--->PS

In other words - the final response (or any provisional response) comes from
a different address than the one that the INVITE was sent to.

I know that AFTER the final response, any request can legitimately come from
a different source than the original request, but what is the proper
behavior when this situation occurs PRIOR to the final response?

Thanks,
Kathleen McMurry

---

From: "Fairlie-Cuninghame, Robert" <[email-masked]>
Date: Sun, 18 Jun 2000 21:13:43 -0700

Hi Jonathan,

It would be nice though if the source authentication could be provided at
the IP layer through IPSEC AH or similar methods, such that the SIP UA could
trust the source address if an SA exists without having to implement
authentication itself (assuming hop-by-hop authentication). Is this a
pipe-dream ? Can anyone see any obvious holes ? There are many issues to
consider but one of them is: who is allowed to send BYE & re-INVITE requests
for a call. I guess one answer is "anyone with an SA" but I was hoping thing
we could narrow it down a bit.

Robert.

-----Original Message-----
From:	Jonathan Rosenberg [mailto:[email-masked]]
Sent:	Tuesday, June 06, 2000 12:21 PM
To:	Fairlie-Cuninghame, Robert
Cc:	McMurry, Kathleen; Sean Olson; [email-masked]
Subject:	Re: [SIP] Request/Responses from other addresses

"Fairlie-Cuninghame, Robert" wrote:
> 
> > > For security purposes, actually, you really do need to check that the
> > > CANCEL came from the same place as the request being cancelled (see
the
> > > minutes of the security task force on this). CANCELs cannot usefully
be
> > > authenticated directly, since they may come from proxies. That aside,
> > > CANCEL can come from anywhere.
> > >
> I take it then that this doesn't apply to BYE requests because they can be
> authenticated directly?

Yes.

> Is there a weaker source address check you could
> apply in the absence of authentication? I can't think of any infallible
> ones.

THere is no such thing as infallible security anyway.

> Requests will not always come from the original source address and the
> Contact address doesn't necessarily infer that the source of future
requests
> will be from that address... although it would help if we could assume
that!

In the case of mobility, the address definitely won't be the same.

> 
> So I guess that without authentication, SIP is very vulnerable to someone
> sniffing packets and then generating their own requests to re-INVITE the
> call to themselves.

Yes; but thats why we have it. 

-Jonathan R.

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (732) 741-7244
http://www.dynamicsoft.com

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