Saturday, July 10, 2004: 11:00 pm (Area "B"): Today's anonymous communication software (such as Mixmaster, Mixminion, Nymservers, JAP, Tor, Anonymizer, etc.) allows people to communicate while concealing their identities from each other and from external attackers. But no deployed system is strong enough to protect every pattern of user behavior against a sufficiently resourceful adversary, and many of them fall to far simpler attacks. In this talk, Nick Matthewson will discuss working attacks against today's anonymity networks, drawing from past technical and social attacks on deployed networks and from recent academic research in traffic analysis, stylometry, and mix-net design. He will present defenses to these attacks when such defenses are known to exist.