Features

net.wars: Security vs security part II

by Wendy M Grossman | posted on 16 June 2006


It's funny. Half the time we hear that the security of the nation depends on the security of its networks. The other half the time we're being told by governments that if the networks are too secure the security of the nation is at risk.

Wendy M Grossman

This schizophrenia was on display this week in a ruling by the US Court of Appeals in the District of Columbia, which ruled in favour of the Federal Communications Commission: yes, the FCC can extend the Communications Assistance for Law Enforcement Act to VoIP providers. Oh, yeah, and other people providing broadband Internet access, like universities.

Simultaneously, a clutch of experts – to wit, Steve Bellovin (Columbia University), Matt Blaze (University of Pennsylvania), Ernest Brickell (Intel), Clinton Brooks (NSA, retired), Vinton Cerf (Google), Whifield Diffie (Sun), Susan Landau (Sun), Jon Peterson (NeuStar), and John Treichler (Applied Signal Technology) – released a paper explaining why requiring voice over IP to accommodate wiretapping is dangerous. Not all of these folks are familiar to me, but the ones who are could hardly be more distinguished, and it seems to me when experts on security, VOIP, Internet protocols, and cryptography all get together to tell you there's a problem, you (as in the FCC) should listen. Together, this week they released Security Implications of Applying the Communications Assistance to Law Enforcement Act to Voice over IP (PDF), which carefully documents the problems.

First of all – and they of course aren't the only ones to have noticed this – the Internet is not your father's PSTN. On the public switched telephone network, you have fixed endpoints, you have centralised control, and you have a single, continuously open circuit. The whole point of VoIP is that you take advantage of packet switching to turn voice calls into streams of data that are more or less indistinguishable from all the other streams of data whose packets are flying alongside. Yes, many VoIP services give you phone numbers that sound the same as geographically fixed numbers – but the whole point is that neither caller nor receiver need to wait by the phone. The phone is where your laptop is. Or, possibly, where your secretary's laptop is. Or you're using Skype instead of Vonage because your contact also uses Skype.

Nonetheless, as the report notes, the apparent simplicity of VoIP, its design that makes it look as though it functions the same as old-style telephones, means that people wrongly conclude that anything you can do on the PSTN you should be able to do just as easily with VoIP.

But the real problems lie in security. There's no getting round the fact that when you make a hole in something you've made a hole through which stuff leaks out. And where in the PSTN world you had just a few huge service providers and a single wire you could follow along and place your wiretap wherever was most secure, in the VoIP world you have dozens of small providers, and an unpredictable selection of switching and routing equipment.

  • You can't be sure any wiretap you insert will be physically controlled by the VoIP provider, which may be one of dozens of small operators.
  • Your targets can create new identities at no cost faster than you can say "pre-pay mobile phone".
  • You can't be sure the signals you intercept can be securely transported to Wiretap Central. The smart terminals we use have a better chance of detecting the wiretap – which is both good and bad, in terms of civil liberties.
  • Under US law, you're supposed to tap only the communications pertaining to the court authorisation; difficult to do because of the foregoing. And then, there's a hole, as the IETF observed in 2000, which could be exploited by someone else. Whom do you fear more will gain access to your communications: government, crook, hacker, credit reporting agency, boss, child, parent, or spouse? Fun, isn't it?

    And then there's the money. American ISPs can look forward to the cost of CALEA with all the enthusiasm that European ISPs had for data retention. Here, the government helpfully provided its own data: a VoIP provider paid $100,000 to a contractor to develop its CALEA solution, plus a monthly fee of $14,000 to $15,000 and, on top of that, $2,000 for each intercept.

    Two obvious consequences.

    First: VoIP will be primarily sold by companies overseas into the US because in general the first reason people buy VoIP is that it's cheap. Second: real-time communications will migrate to things that look a lot less like phone calls. The report mentions massively multi-player online role-playing games and instant messaging. Why shouldn't criminals adopt pink princess avatars and kill a few dragons while they plot?

    It seems clear that all of this isn't any way to run a wiretap program, though even the report (two of whose authors, Landau and Diffie, have written a history of wiretapping) allows that governments have a legitimate need to wiretap, within limits. But the last paragraph sounds like a pretty good way to write a science fiction novel. In fact, something like the opening scenes of Vernor Vinge's new Rainbows End.

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    Wendy M. Grossman’s Web site has an extensive archive of her books, articles, and music, and an archive of all the earlier columns in this series. Readers are welcome to post here, at net.wars home, follow on Twitter or send email to netwars(at) skeptic.demon.co.uk (but please turn off HTML).