Simson Garfinkel analyses Skype - Open Society Institute

[Dan Kaminsky]

>Actually it's not that bad: using SIP, the RTP packets can be protected by
>SRTP (RFC3711, with an opensource implementation from Cisco at
>http://srtp.sourceforge.net/ )
>
SRTP...heh.  Take a look at RFC3711 for a second.

"

   Specification of a key management protocol for SRTP is out of scope
   here.  Section 8.2, however, provides guidance on the parameters that
   need to be defined for the default and mandatory transforms.

"
VOIP KEX.  *shudders*  Voice is...unique.  Session redirection is a 
first class function, as is active proxying, up to and including proxies 
that are payload-destructive (conference stream mixing).  KEX in such an 
environment is a really painful problem, compared to the relatively 
solvable one of specifying a loss-tolerant encryption protocol.  So, 
they only solved the latter, and figured something would come along for 
the former.

Didn't really happen.

(Full Disclosure:  I work for Avaya, whose had a proprietary KEX 
implementation that handles all of this for the last few years.  So it's 
not an unsolvable problem or anything like that.  It's just really 
annoyingly hard.)

--Dan


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