Subject: [Sipping] Some random thoughts on UA, security, and content-indirections`

From: "Cullen Jennings" <[email-masked]>
Date: Wed, 21 Aug 2002 11:09:36 -0700

I've been thinking about issues around UAs that, due to various constraints,
have very limited capabilities but still which to participate in the type
things that are going to require signed sipfrags.

I also notice an interesting property of the content-indirection. When a UAC
puts a content indirection URL in a messages, it does not need to be valid
yet, however, it does need to be valid by the time it arrives at the UAS and
the UAS goes to use it. (ok - I know it is more complex, messages in the
other direction, proxies could use the URL, whatever, but pretend it is like
this for a second)

The UAC could insert content indirection URLs for all the places where it
should be doing sipfrag however it would not actually generate the content
any of these URL pointed to. It would then send the message to a "Trust
Agent Proxy" that the UAC trusted and had delegated all of it's signing
authority too. The "Trust Agent Proxy" would create, on behalf of the UAC,
all the content for the signed sipfrags that the UAC should have created and
put them in the right place. It would then, acting like an outbound proxy,
forward the message to the UAS which would retrieve these as normal and
would be unaware that the "Trust Agent" created them on behalf of the UAC.

Obviously these ideas are still half baked but I think our security model is
going to make us start thinking more about delegating trust.

Cullen

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