Subject: Re: [Sip] re: SMIME in SIP

From: Rohan Mahy <[email-masked]>
Date: Sun, 17 Feb 2002 09:16:25 -0800

Ofir,

I was referring only to SIP over UDP.  No one was suggesting 
RTP over TLS for example.  ;-)

btw: the AVT WG is working on Secure RTP

thanks,
-rohan

>Rohan,
>
>>>4) TLS doesn't address UDP. IPsec WG is working on
>>>  NAT traversal
>>>
>> 
>> UDP doesn't work well in the Internet at large anyway.  
It's support is
>> still around for backwards compatibility, and for use in 
specialized
>> layer2 domains where RTT is expensive; these domains 
usually run what
>> amounts to a private network.  IPsec is probably a good 
thing in those
>> networks, and the spec allows for that.
>
>
>Umm, DNS? Streaming Media? 
>
>Your own voice sampling transporting protocols such as RTP?
>
>Do not dismiss UDP that fast. It has it's usages :)

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---

From: "Peterson, Jon" <[email-masked]>
Date: Mon, 18 Feb 2002 14:29:37 -0600

One note below.

Jon Peterson
NeuStar, Inc.

> -----Original Message-----
> From: Christian Huitema [mailto:[email-masked]]
> Sent: Monday, February 18, 2002 12:09 PM
> To: [email-masked]; Michael Thomas
> Cc: Rohan Mahy; [email-masked]
> Subject: RE: [Sip] SMIME in SIP
> 
[snip]
> 
> However, if we want to use TLS seriously, we need to resolve a security
> issue that is caused by the use of SRV records as specified in
> draft-ietf-sip-srv-04.txt. In short, DNS records can be spoofed. A
> hacker can manage to spoof the SRV record for "_sip._tls.microsoft.com"
> to point to "hackers-are-us.tv", thus intercepting all the SIP traffic
> to Microsoft. The basic usage of TLS will only guarantee that the name
> to address mapping is genuine, i.e. that the target is really the
> authorized server for "hackers-are-us.tv", but that will not make us a
> whole lot of good. So, when we say "check the certificate", we should
> really check for a link to the initial domain, pre-SRV.

We hope that the new SIPS mechanism can help to address the DNS attack
problem; it has been integrated into sip-srv-05. Also, if you look at the
security solutions in bis07 (specifically 22.3.2.2), we recommend exactly
the reference integrity check you describe above - that when you check the
certificate of a remote party in a transaction, that you compare the
identity/hostname asserted by the certificate with the resource you are
attempting to contact.

> -- Christian Huitema

---

From: "Christian Huitema" <[email-masked]>
Date: Mon, 18 Feb 2002 12:37:47 -0800

> Christian Huitema writes:
>  > Actually, SIP's traffic is more analogous to DNS than to streaming
> media
>  > and, yes, DNS does not work well. See
>  > http://www.huitema.net/papers/NetMeasureV2.doc for the gory
details.
> 
>    Well, I don't get it. Why is it that MGCP used
>    UDP? And I seem to recall Van speaking up in Oslo
>    during MEGACO saying that using UDP and ALF was
>    not only OK, but a Good Thing.

UDP & ALF relate to the possibility to tie the network behavior closely
with the application priorities, e.g. to not retransmit messages that
are now obsolete, to replace retransmissions by summaries of the new
state, etc. This is OK, if you can verify two hypotheses: 1) that there
is a long term association between the two parties, so you can build up
some resiliency mechanism in the exchange; 2) that you have some form of
underlying security to provide protection against spoofing attacks.
Number (1) is true for MGCP, since there is a long term association
between the gateway and the controller. Deploying MGCP without some
response to (2) is indeed insecure. Neither hypothesis is true for DNS:
packets pop out of the blue from random locations; you suffer from the
Internet wide packet loss rate of about 3%, and have no better way to
cope than coarse timer retransmission; source and response spoofing can
be used in all kinds of attacks. We can argue that this is a necessary
evil in the case of DNS, be we don't have to by that for SIP. We could
argue that there hypothesis (1) is verified between a UA and the local
proxy, but you will still need security; in the case of random
proxy-proxy exchanges, neither hypothesis stands, so you really want to
use security + reliability, hence TLS.

-- Christian Huitema