Eavesdropping software the team has developed cannot yet decode an entire conversation, but it can search for chosen phrases within the encrypted data. This could still allow a criminal to find important financial information conveyed in the call, says Fabian Monrose, another team member.
The software breaks down a typed phrase to be listened for into its constituent sounds using a phonetic dictionary. A version of the phrase is then pasted together from audio clips of phonemes taken from a library of example conversations, before finally being made into a stream of VoIP-style packets.
That gives an idea of what the phrase would look like in a real VoIP stream. When a close match is found in a real call, the software alerts the eavesdropper.
Jargon catcher
In tests on example conversations, the software correctly identified phrases with an average accuracy of about 50%.
