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Spoofing trick foxes wiretaps

Hanging on the telephone

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Security researchers have discovered a way to trick some wiretap systems used in the US into switching themselves off, while leaving phones still usable. University of Pennsylvania researchers have also discovered it might be possible to falsify a record of numbers dialed recorded by older spy devices. "These countermeasures do not require cooperation with the called party, elaborate equipment, or special skill," the researchers write in a paper Signaling Vulnerabilities in Wiretapping Systems published in the IEEE's Security & Privacy journal this week.

The trick involves spoofing a continuous low-amplitude "C-tone" audio signal on a monitored line that mimics the "on-hook" signal, thereby fooling some older wiretap systems to suspend audio recording. "Most loop extender systems, as well as at least some CALEA [Communications Assistance for Law Enforcement Act] systems, appear to be vulnerable to this countermeasure," the researchers say. But most (though not all) modern systems won't be fooled by the trick. The upshot is that paranoid crooks stand a one in ten chance of making unrecorded calls providing they can live with a buzz on the line. The ploy does not give targets any clue about whether they are being monitored or not.

Matt Blaze, lead researcher and an associate professor of computer science at the University of Pennsylvania, told the New York Times that the research has "implications not only for the accuracy of the intelligence that can be obtained from these taps, but also for the acceptability and weight of legal evidence derived from it."

However an FBI spokeswoman told the paper that its experts already knew that older wiretap systems might be thwarted. Although as many as 10 per cent of state and federal wiretaps might be vulnerable "it's not considered an issue within the FBI," she said.

Independent security experts say the research, which has been made available to law enforcement agencies, illustrates that the war against crime is increasingly been fought on a technological front. Fortunately most crooks are not cyber-savvy, at least according to one expert.

"If you are a determined bad guy, you will find relatively easy ways to avoid detection," said Mark Rasch, a former federal prosecutor who is now chief security counsel at Solutionary Inc. "The good news is that most bad guys are not clever and not determined." ®

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