Re: [rtcweb] Fwd: New Version Notification for draft-uberti-rtcweb-turn-rest-00.txt

Martin Thomson <martin.thomson@gmail.com> Mon, 08 July 2013 21:43 UTC

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Date: Mon, 8 Jul 2013 14:43:35 -0700
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From: Martin Thomson <martin.thomson@gmail.com>
To: Justin Uberti <juberti@google.com>
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Subject: Re: [rtcweb] Fwd: New Version Notification for draft-uberti-rtcweb-turn-rest-00.txt
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On 8 July 2013 13:09, Justin Uberti <juberti@google.com> wrote:
> The issue with using short term credentials, without a nonce, is the
> possibility of replay attacks by an eavesdropper.

It is no less vulnerable than having the long term credential set
(username, nonce, realm, and password) overheard.  Assuming that the
lifetime of the password is the same in both cases.  In either case,
the link that the eavesdropper is required to attack is the HTTP link.

> Passing realm and nonce solves this [...]

I was suggesting that since you have spent some very expensive
round-trips getting this information, there are no advantages in
spending yet another round-trip on a challenge.  I don't think that
passing realm and nonce is a good idea in practice - it creates a
tighter coupling between this new thing and the TURN server.

In practice, a master nonce is not quite what you need, you need a
nonce-generator function, or a line to the TURN server whereby you
query for every request you get.  The former imposes too-strong
constraints on implementations, the latter renders much of the
advantages of something like this moot.