Privacy Enhancing Technologies 4th International Workshop, PET 2004, Toronto, Canada, May 26-28, 2004, Revised Selected Papers

The ?rst workshop in this series was held at the International Computer S- ence Institute in Berkeley and was published as LNCS 2009 under the name "Workshop on Design Issues in Anonymity and Unobservability." Subsequent Privacy Enhancing Technologies (PET) workshops met in San Francisco in 2002 (LNCS2482)andDresdenin2003(LNCS2760).Thisvolume, LNCS3424, holds the proceedings from PET 2004 in Toronto. Our 2005 meeting is scheduled for Dubrovnik, and we hope to keep ?nding new and interesting places to visit on both sides of the Atlantic - or beyond. An event like PET 2004 would be impossible without the work and dedi- tion of many people. First and foremost we thank the authors, who wrote and submitted 68 full papers or panel proposals, 21 of which appear herein. The Program Committee produced 163 reviews in total. Along the way, they were assisted in reviewing by Steven Bishop, Rainer Bohme, Sebastian Clauß, Claudia D ́ ?az, Richard E. Newman, Ulrich Flegel, Elke Franz, Stefan Kopsell, Thomas Kriegelstein, Markus Kuhn, Stephen Lewis, Luc Longpre, Steven M- doch, Shishir Nagaraja, Thomas Nowey, Peter Palfrader, Lexi Pimenidis, Klaus Ploessl, Sivaramakrishnan Rajagopalan, Marc Rennhard, Leo Reyzin, Pankaj Rohatgi, Naouel Ben Salem, Sandra Steinbrecher, Mike Szydlo, Shabsi Wal?sh, Jie Wang, Brandon Wiley, and Shouhuai Xu.