Subject: RE: [Sip] A sips: trial balloon for you to shoot down

From: "Sanjay Sinha \(sanjsinh\)" <[email-masked]>
Date: Wed, 1 Nov 2006 13:35:28 -0500

>-----Original Message-----
>From: David Benoit [mailto:[email-masked]] 
>Sent: Wednesday, November 01, 2006 10:28 AM
>To: Sanjay Sinha (sanjsinh)
>Cc: IETF SIP List; Dean Willis
>Subject: Re: [Sip] A sips: trial balloon for you to shoot down
>
>On Tue, Oct 31, 2006 at 02:00:51PM -0500, Sanjay Sinha 
>(sanjsinh) wrote:
>> Don't like the PSTN gateway limitation. As was mentioned in 
>an earlier 
>> email, if signaling reaches PSTN gateway, it has reached UAS.
>
>I think you mean UAC.  As far as SIP is concerned, the gateway 
>is the client.
No I meant UAS. For a call originated from a SIP UA to a pstn user,
gateway is acting like a UAS.

Sanjay.
>
>David
>--
>[email-masked] | phone: 902-832-2649  fax: 
>902-832-1015  "Complex problems have simple, neat and wrong 
>solutions" - H. L. Menken
>
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_______________________________________________
Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [email-masked] for questions on current sip
Use [email-masked] for new developments on the application of sip

---

From: Dean Willis <[email-masked]>
Date: Wed, 1 Nov 2006 15:07:15 -0600

> gateway is acting like a UAS.

Right. And all of the signaling from SIP is being mapped into some  
other signaling protocol and sent beyond a transitive trust boundary.  
The gateway simply doesn't know where its goingor what is going to  
happen "out there". Consequently, the gateway knows that it cannot  
assure transitive trust with respect to signaling integraity, and  
since it cannot insure transitive trust, it cannot use sips:.

Using sips: means "I guarantee that you can trust me to make sure  
this channel is protected to the minimal standard defined by sips:".  
If you can't meet that commitment, you just can't use sips:.

--
Dean

---

From: "Hadriel Kaplan" <[email-masked]>
Date: Wed, 1 Nov 2006 16:23:09 -0500

> From: Dean Willis [mailto:[email-masked]]
> Sent: Wednesday, November 01, 2006 4:07 PM
> 

I'm curious: what is it specifically you think you're protecting by using
sips, that DOES cross the pstn boundary, and thus would be "leaked"?  I mean
most of any info that crosses into the pstn is either deducible in sips in
some cases too, or doesn't cross, so I'm really curious what it is you think
you'd be losing.

-hadriel

---

From: Dean Willis <[email-masked]>
Date: Wed, 1 Nov 2006 15:37:28 -0600

> some cases too, or doesn't cross, so I'm really curious what it is  

Given some of the things that can be encoded in QSIG and ISUP and  
whatnot, I'm sure there's a surprising amount of information that  
could be leaked.

let's ask the converse: If you're engaging in a telephone call that  
you expect to have sent onto the PSTN, what are you hoping to protect  
by insisting that the call fail if all the IP signaling links are not  
wrapped in TLS? Keep in mind that you KNOW that SIP elements  
compliant to Best Current Practices will encrypt everything that they  
can possibly encrypt even if you don't use sips: . . .

--
Dean

---

From: "Hadriel Kaplan" <[email-masked]>
Date: Wed, 1 Nov 2006 18:09:45 -0500

> Sent: Wednesday, November 01, 2006 4:37 PM
>

Indeed, but as I understand it unless it was already in an ISUP/QSIG
attachment in sips, most of the info that would be generated is not from sip
itself but defaults, or could be deduced by a sips session traffic as well
(without seeing inside).  For some cases, anyway.
And if the ISUP/QSIG info _is_ in the sips to begin with, then clearly it
came from or knows it is going to the pstn.

> can possibly encrypt even if you don't use sips: . . .

That's not the only converse, and I personally wouldn't send it as sips, but
for that question someone's answer could be: I would be using sips to
protect my sdesc keys for srtp, because I feel it is easier to remotely
monitor/harvest/etc. traffic on the public Internet than on the pstn, and I
want the media secured.  So I want it to fail so I know to speak in
pig-latin, or not type my pin code, or whatever.  I may have typed in a
sips:[email-masked], but if it got retargeted to his cell through a
provider staying sips I don't expect them to reject the request just because
I am using sips and it would go across the pstn.

-hadriel