Interesting:

The researchers say they’ve found a vulnerability in U.S. law enforcement wiretaps, if only theoretical, that would allow a surveillance target to thwart the authorities by launching what amounts to a denial-of-service (DoS) attack against the connection between the phone company switches and law enforcement.

[…]

The University of Pennsylvania researchers found the flaw after examining the telecommunication industry standard ANSI Standard J-STD-025, which addresses the transmission of wiretapped data from telecom switches to authorities, according to IDG News Service. Under the 1994 Communications Assistance for Law Enforcement Act, or Calea, telecoms are required to design their network architecture to make it easy for authorities to tap calls transmitted over digitally switched phone networks.

But the researchers, who describe their findings in a paper, found that the standard allows for very little bandwidth for the transmission of data about phone calls, which can be overwhelmed in a DoS attack. When a wiretap is enabled, the phone company’s switch establishes a 64-Kbps Call Data Channel to send data about the call to law enforcement. That paltry channel can be flooded if a target of the wiretap sends dozens of simultaneous SMS messages or makes numerous VOIP phone calls “without significant degradation of service to the targets’ actual traffic.”

As a result, the researchers say, law enforcement could lose records of whom a target called and when. The attack could also prevent the content of calls from being accurately monitored or recorded.