Matt Blaze and company have a new paper just out entitled Signaling Vulnerabilities in Wiretapping Systems, which details a number of problems with the methods and equipment normally used by law enforcement to tap phone equipment. These include vulnerabilities that allow the surveilled party to make it appear to call numbers other than the one reached, to disable recording of specific calls and to just generally make it hard for tappers. Interesting stuff, and using relatively straightforward ideas and methodology.

Matt is a remarkable guy, I particularly liked his paper Safecracking for the computer scientist.