A powerful method for extracting information from supposedly secure systems is side-channel attacks: cryptanalytic techniques that rely on information unintentionally leaked by computing devices. Most side-channel attack research has focused on electromagnetic emanations (TEMPEST), power consumption and, recently, diffuse visible light from CRT displays. The oldest eavesdropping channel, namely acoustic emanations, has received little attention. Our preliminary analysis of acoustic emanations from personal computers shows them to be a surprisingly rich source of information on CPU activity. This fact should be obvious to anyone who's ever tried to make low SNR recordings with a $5 sound card. Acoustic Cryptanalysis | 
