[guardian-dev] A Network Analysis of Encrypted Voice over OSTN

[Patrick B]

I haven't been able to test this, but this is the assumption, yes.
ZRTP setup packets would be identifiable with application filtering
and could probably be selectively blocked without any user notice. The
discerning user might notice, but this would be a problem for accounts
like OSTN in which a user might just expect encryption to always work.

I would assume for now that ZRTP could be silently blocked. Since
right now opportunistic encryption is used, both clients use RTP until
they see ZRTP hello packets. All you need to do is block those hello
packets and it would appear that the other client has ZRTP off.

Adding a Force-ZRTP to the client would solve this problem. Blocking
ZRTP would just block the call then.

-Patrick

On Fri, Jul 6, 2012 at 8:56 AM, Tom Ritter <tom at ritter.vg> wrote:
> Good analysis.
>
> Would a man in the middle be able to swallow the ZRTP setup packets and
> prevent encryption without being detected*? I can't imagine RTP provides
> integrity...
>
> *Other than the parties knowing they don't have encryption, of course.
>
> -tom
>
>
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