[liberationtech] WebRTC - The next big surveillance machine

[Tony Arcieri]

On Thu, Jan 23, 2014 at 11:52 AM, carlo von lynX <
lynX at time.to.get.psyced.org> wrote:

> > say it not secure. WebRTC is compatible with ZRTP key-authentication
> which
> > builds in a video-based auth scheme and should stop MITM attacks (last
> time
>
> You can't diffie-hellman yourself out of a MITM. If the fundamental link
> is unsafe, you can make all the ephemeral keys you like - the observer can
> trace them all.
>

You should take a look at how ZRTP actually works, particularly Matt
Green's analysis:

http://blog.cryptographyengineering.com/2012/11/lets-talk-about-zrtp.html

ZRTP authentication works by negotiating what's called a "short
authentication string" between peers. If there's no MitM, both sides will
see the same string.

To authenticate, you start a voice/video call. You will see the person
you're expecting, but at this point the link is insecure and may be MitMed.

However, Alice can read off the Short Authentication String to Bob. Short
of fancy realtime video editing and voice impersonators, the string will be
incorrect if the connection is being MitMed.

Once this has been done successfully once, ZRTP stores some "continuity
data" so the next time you authenticate to the same person, the previous
authentication will ensure future connections are secured.

-- 
Tony Arcieri
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