[Sip] comments on draft-zourzouvillys-sip-via-cookie-02

[Jonathan Rosenberg <jdrosen at cisco.com>]

Theo,

Thanks for writing this up.

A few comments.

Firstly, it seems that the easiest solution is just 'use tcp'. This is 
one of many reasons (and growing) why we need to be pushing 
implementations to tcp.

Secondly, if you want to do this for UDP, you could instead use 
anonymous authentication. Then, the existing nonce takes on the role of 
a cookie. I suspect that anonymous authentication is not widely 
implemented, but neither is a new protocol. That said, I think the right 
answer still is 'use tcp'.

Finally, the media portion of this attack, as you point out, is far more 
disruptive. That attack does not require spoofing even; just listing the 
IP address/port of the target in the SDP of the INVITE. We were calling 
this the 'voice hammer' attack, originally documented here:

http://tools.ietf.org/html/draft-rosenberg-mmusic-rtp-denialofservice-00

and described in Section 18.5.1 of ICE. The via cookie mechanism you 
propose, SIP-over-TCP, or anonymous authentication, none of them fix 
this attack. AFAIK, ICE is the only remedy.

-Jonathan R.



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Jonathan D. Rosenberg, Ph.D.                   111 Wood Avenue South
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