Thursday, February 09, 2006

Spy vs. Spy, or how to beat wire taps


Are your phones being tapped? Do you hear heavy breathing when you send e-mail? Is Incurious George listening in while you discuss male menopause with you neighbor? —Cheer up fella. You can fight wire taps.

According to Seucrity and Privacy Journal, you can screw ‘em. Or rather some of them. There actually are ways to make tapping your phone difficult or impossible. One presumes the terrorists already know this so why not us folks? The research comes from the University of Pennsylvania, including Micah Sherr, Eric Cronin, Sandy Clark, and Matt Blaze, and all the information is public.

The most obvious form of wire tapping is a direct electrical connection to your phone line, literally, a tap. Law enforcement officers would use a small device called loop extender or dial-up slave which sends any audio on the line to the cops’ line, re-encodes the signals and performs level equalization. Equipment at the law enforcement agency turns on when you dial the phone, records the number and decodes the conversation. That’s not used very much any more, it’s analog, easy to beat and clumsy. Most tappers use CALEA taps. That is done at the phone company, which (presumably only when a court order permits) intercepts the subject’s conversations and sends it to the law enforcement agency. The cops (which means, one presumes, the FBI, NSA, CIA and everyone else) has one line that records the number and another that records the conversation. The phone company just throws some switches.

The direct tap is fairly easy to recognize, the researchers say. First, you might just see it. More important, the tapping changes the nature of the transmission characteristics and that can be detected with off-the-shelf equipment. Some folks may want to hack the phone company.

CALEA taps are another story. (Encrypting telephone messages so they can’t be deciphered is hard to do and the equipment hard to find.) One way to beat CALEA is to use a call-forwarding service. Flood your lines with irrelevant calls forwarded to another number and while the authorities are trying to wade through that, make the call you want. The Penn researches say it works. There also are ways of faking phone numbers.

The weakness in CALEA is something called the C tone, which tells the phone line that the phone is idle. When the C tone stops it cues the eavesdroppers that you are making a call. The C tone consists of two frequencies. So, go generate your own. There are phones that have a C tone button you just press and the tone is played, turning off the tappers. You can also generate same from equipment purchased on E-Bay or Radio Shack. Generate a tone loud enough to turn off the tap but low enough to carry on a conversation. They'll never know you called. There is even software you can download that will do it.

The researchers point out that law enforcement agencies have gone to great lengths to mitigate these decoy activities, but hint broadly, they may not be as good at it as they think.

E-mail is even easier to block. Any number of commercially available programs can encrypt messages enough to give the NSA conniptions. They can be broken but only with great effort. It’s also possible to generate phony packets in internet transmissions to confusion listeners. You send out two messages, one the eavesdroppers can play with while you carry one the real communication. See here.

Presumably, all the world’s bad guys know about this stuff. They are not idiots. It’s only we innocent folks that are kept in the dark.

[Cartoon—DC Comics]

1 comment:

Bill Thomasson said...

In a way I was surprised by the comment that encrypting telephone calls was hard to do and the equipment hard to find. As you'll recall, Bill Clinton proposed a law that would have required every telephone in the country to have embedded encryption ("Clipper Chip"). And by executive order, every telephone the federal government owns actually does have one.

The kicker, of course, was that the federal government would always have the decryption key. So if it's the feds you're trying to hide from, this doesn't help.