Subject: [Sipping] Feedback on draft-jennings-sipping-multipart-00.txt

From: Gonzalo Camarillo <[email-masked]>
Date: Fri, 04 Mar 2005 13:10:47 +0200

Hi,

the following draft contains examples of alternative offers where one 
proposes SRTP and the other plain RTP.

http://www.ietf.org/internet-drafts/draft-jennings-sipping-multipart-00.txt

We need to include discussions on biddown attacks and how a 
man-in-the-middle can make endpoints use the least secure media 
transport between them.

Given that the idea is to be able to interoperate with endpoints that do 
not support S/MIME, there is no way around the biddown attack, but at 
least we should mention it in the security considerations. We should 
describe the security implications of using this mechanism to offer 
different offers with different security levels.

In any event, this work is needed for SDPng migration, and therefore, it 
is important.

Thanks,

Gonzalo

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From: Paul Kyzivat <[email-masked]>
Date: Fri, 04 Mar 2005 09:21:27 -0500

Gonzalo Camarillo wrote:
> least we should mention it in the security considerations.

Adding discussion is a good idea. Some of us have discussed this 
privately in the past. General conclusion (at least mine) is that UAs 
supporting optional SRTP need to include an indicator in their UI of 
whether an established session is secure or not. Based on that the 
participants can adjust the content of their session - discussing only 
"safe" topics when the session isn't private.

If the participants believe they both have endpoints that should be able 
to establish a secure session, yet the sessions that get established 
between them are not secure, they can conclude that something in the 
infrastructure they are using is blocking their use of secure sessions. 
Based on that realization they can take whatever actions they feel 
appropriate - switch to a different infrastructure, file a complaint 
with the administrators of the infrastructure, etc.

	Paul