Subject: RE: [Sip] Ciphersuites in SIP

From: "Samir Srivastava" <[email-masked]>
Date: Fri, 4 Aug 2006 15:39:24 -0500

I am  busy with other stuff. 

Having bugs at other places, doesn't give us excuse to not to fix it.
Later  write in details. It does expose the Calling numbers etc to the
spammers. E164 no are much more densly packed as compared to email
addresses. Do we want to design another numbering plan. See how we ran
out of IP addresses in V4 etc....

Thx
Samir

>Again, do you have any evidence this is a problem in real life?
>There are lots of insane and dangerous things an operator can
>do. Why should we have protocol support for just this one?

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From: Eric Rescorla <[email-masked]>
Date: Fri, 04 Aug 2006 14:21:11 -0700

I have no idea what you're talking about here.

-Ekr

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From: "Samir Srivastava" <[email-masked]>
Date: Fri, 4 Aug 2006 16:45:21 -0500

Hi Eric,

Spammers can learn the potential targets by tapping on the wire. We need
to avoid more choices for them. If my phones keep on ringing from the
spam calls, and anti-spit solution cannot figure it out. We will be left
with only using with the different number/SIP URI etc. Gradually we will
run out of this. 

We should avoid the places where spammers can learn the targets.
This is one bigger aspect, other issues comes from the less secure hops
like call pattern tracking etc. 

IMHO, we need cipher-suite exposed by the same notion we have TLS
exposed in SIP. Refer the "Cheater Proxy Motivation" in the other email.

Thx
Samir

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From: Eric Rescorla <[email-masked]>
Date: Fri, 04 Aug 2006 15:04:08 -0700

> with only using with the different number/SIP URI etc. Gradually we will

You do realize that people's phone numbers are basically public
information and that you can buy CDs with lists of people's
names and numbers, right?

> exposed in SIP. Refer the "Cheater Proxy Motivation" in the other email.

I don't find this argument about cheating proxies at all convincing.

Consider the following chain of SIP agents:

Alice --- Atlanta --- Alberta --- Biloxi -- Bob

Now, imagine that Alberta is a cheating proxy and wishes to use
a weak cipher suite to connect to Biloxi. Because Biloxi inserts
the information about what cipher suite was used, Bob is aware
of the algorithms. However, he doesn't know what Alice actually
wanted. Maybe Alice *wanted* those weak algorithms. On the
other hand, Alice's only information about what algorithms were
used comes through Alberta, so it can't tell that Alberta is
cheating.

Once again, the basic assumption behind SIPS security is that
the proxies are trusted. Attempts to patch this without using
end-to-end mechanisms seem likely to fail.

-Ekr

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From: Eric Rescorla <[email-masked]>
Date: Fri, 04 Aug 2006 15:04:08 -0700

-Ekr