more on FCC not Schizo at all

[David Farber <dave () farber net>]

Begin forwarded message:

From: Bill Stewart <bill.stewart () pobox com>
Date: August 9, 2005 11:26:54 AM EDT
To: declan () well com
Cc: hugh () hughcrawford com
Subject: RE: [IP] FCC not Schizo at all


Hugh Crawford's disagreement with Declan misses a critical technical  
distinction, and the services, particularly Skype, are moving in more  
tappable directions. Most modern VOIP protocols use two separate  
kinds of connections - a signalling connection to set up the call,  
and a media connection between the callers.

But any of the centralized services that connect to the public  
telephone network, like Vonage and AT&T CallVantage and possibly  
SkypeIn/SkypeOut, have a hook into the regulated infrastructure where  
wiretapping can happen.
For an outbound only service, the trunk to the PSTN is normally  
shared, so a given caller's call might show up on any random channel,  
and eavesdropping is easier if the service provider can be bullied  
into identifying which targeted caller is on which channel, or which  
caller is calling a targeted callee, and it's similar to the  problem  
of eavesdropping on a PBX or hotel phone system.
Depending on how the network handles CallerID, it may even be easy to  
get from the trunk signalling. It's possible to design a  
decentralized system that uses PBXs or individual phones to deliver  
calls to the local telco providers (at least for outbound calls), and  
that would be much harder to wiretap.

With the original Skype service, the non-US-based company sells the  
software, and the signalling is mostly done by peer-to-peer networks,  
but with most other VOIP protocols, the signalling happens at some  
server that may or may not be under the jurisdiction of some  
regulator (in the case of SIP, the protocols support proxies and  
hierarchy, so you may have a PBX-like signalling server talking to a  
carrier.)

In the purely-IP world, if the media channel is encrypted, it's hard  
to eavesdrop on it directly, but the fans of wiretapping are sure to  
decide that the signalling channel is similar to old-style pen- 
register traces, and the accounting (if any) is similar to phone  
company accounting, and therefore they'll try to get access to that  
information at any regulatable provider the way they do with phone  
records today, possibly without the niceties of full wiretap warrants.
Also, when the signalling server can be bullied into cooperating, a  
wiretap is not much different from a three-way conference call, and  
it gets around the problems of encrypted media channels (though that  
can usually be done by having the signalling server tell the  
endpoints to set up the call unencrypted and using ISP wiretaps.)    
Those attacks are much easier when the servers are managed by a  
regulatable carrier - it's not possible to tell non-US software  
companies to build in backdoors, and it's hard to get PBXs to  
cooperate in wiretapping, not only because they're not regulated, but  
because they're often managed by one of the targets of the wiretap so  
you can't do it without them noticing.

By the way, too many of the big SIP controllers on the market don't  
usually enable media-channel encryption, especially for calls to  
carrier-provided PSTN gateways.  It's very frustrating.

                        Bill Stewart




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