Subject: [Sip-security] New internet drafts on security

From: Jari Arkko <[email-masked]>
Date: Mon, 03 Dec 2001 18:07:26 +0200

I posted this a while back on the sip list but
began to worry that maybe I should have done it
on this list instead. Sorry for the double-post
but here goes. Comments and discussion very
wellcome:

Dear all,

We've published two new internet drafts around security and
SIP. They may take a few days to get to the official I-D
directories so I'll list below some URLs from which you
can access them in the meantime.

The first draft [1] is titled "HTTP (SIP) Authentication with
EAP". HTTP EAP authentication enables SIP and HTTP to be
authenticated using any of the methods supported in EAP,
a generic authentication framework used in PPP, IPsec remote
access, and various other situations. It is useful for the SIP
protocol because it opens up several new authentication methods
without additional specification work: token cards, public
keys, SRP, 2g/3g sim cards, and so on. These can be run both
h2h and e2e as desired, and without requiring intermediate
nodes to understand it. For instance, strong e2e authentication
could be run even if the hops were protected using some lower
layer method. Similarly, corporate networks could use this as
a client authentication method under TLS, reusing the token
cards and authentication databases the company already has
for other purposes. This draft also satisfies one of the
requirements in draft-garcia for supporting legacy
authentication in SIP.

The second draft [2] is titled "Security Mechanism Agreement
for SIP Connections". The purpose of this draft is to (a)
correct a vulnerability in HTTP Digest authentication for
man-in-the-middle attackers, and (b) to allow SIP peers
to *securely* pick the security method they are going to
use. A number of proposals have been made that could also
be used for 'negotiation', but this proposal attempts to
provide security against man-in-the-middle attackers.
On small networks policy configuration and software updates
are sufficient to deal with these attacks, but on large
networks that evolve over time, it isn't possible to demand
all devices must support the latest and strongest methods
and algorithms, yet where such support is available it should
be possible to take advantage of it without allowing trivial
attacks to downgrade the security. The draft works for both
the hop-by-hop and end-to-end cases, and as above satisfies
one of the requirements in draft-garcia for secure agreement
of access domain security mechanisms.

Of course, the above drafts are just one way of solving
a part of the complete problem. I'd like to invite discussion
on what the complete SIP security picture should be, as
well as various alternative approaches. For instance,
both Michael Thomas and Henning Schulzrinne have described
multi-security-scheme frameworks, perhaps we should discuss
if [2] is needed in such contexts. Also, some EAP methods
are capable of producing session keys in a secure manner,
these would potentially be useful for doing some sort of
symmetric crypto afterwards, maybe with Sanjoy Sen's draft
or with Michael's 'preshared secret crypto system'.

Perhaps the sip-security list is the appropriate list to
discuss these further. What about the next meeting, how
are the various security issues going to be discussed
in there? The framework proposal(s)? Various drafts filling
3gpp wishes? Other stuff?

Jari
----
[1] http://standards.ericsson.net/sip/drafts/draft-torvinen-http-eap-01.txt
[2] http://standards.ericsson.net/sip/drafts/draft-arkko-sip-sec-agree-00.txt

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