[Asterisk-Security] Opportunistic encryption

[Enzo Michelangeli]

----- Original Message ----- 
From: "John Todd" <jtodd at loligo.com>
To: "Asterisk Security Discussion" <asterisk-security at lists.digium.com>
Sent: Saturday, July 22, 2006 1:27 AM
Subject: Re: [Asterisk-Security] Opportunistic encryption

[...]
>   3) "Man in the Middle" mode, where Asterisk creates two separate ZRTP 
> legs to different ZRTP clients.  While this sounds like a security risk, 
> it is actually a fairly desirable situation.  Many calls need to be 
> recorded, or monitored for DTMF, or inserted into app_conference for group 
> discussion.  Having each leg of the call encrypted to the Asterisk server 
> but not encrypted in an "end-to-end" fashion would be frequent, I suspect. 
> The users could still verify that their calls were encrypted to the core, 
> and interception would not be possible except on the Asterisk server 
> itself.

Why not? AFAIK, in ZRTP a man in the middle is detected through biometric 
authentication (the two users at the endpoints compare a common hash while 
recognizing each other's voice). Once you break this mechanism with a 
(supposedly) trusted MiM, you can't exclude the existence on a _second_ MiM 
in the chain.

Also, I wouldn't be so sure about the impregnability of the Asterisk box. 
Incidentally, concerns of this type represented an important factor in the 
failure of WTLS to be accepted for securing e-commerce transactions on 
mobile phones: the WTLS<->SSL gateway was vulnerable to hacking, and 
therefore untrusted.

Enzo