You are holding the proceedings of Eurocrypt 2009, the 28th Annual Inter- tional Conferenceon the Theoryand Applications of CryptographicTechniques. This conference was organized by the International Association for Cryptologic Research in cooperation with the Horst Gort ¨ z Institute for IT-Security at the Ruhr-Universit¨ at Bochum. The local organization received additional support from several sponsors: Horst G¨ ortz Stiftung, Deutsche Forschungsgemeinschaft, Bochum 2015, Secunet, NXP, IET, Taylor & Francis, AuthentiDate. The c- ference was held in Cologne, Germany. The Eurocrypt 2009 Program Committee (PC) consisted of 29 members, listed on the next page. There were 148 submissions and 33 were selected to - pear in this volume.Eachsubmissionwasassignedto at leastthreePCmembers and reviewed anonymously. During the review process, the PC members were assisted by 131 external reviewers.Once the reviews were available,the comm- tee discussed the papers in depth using the EasyChair conference management system. The authors of accepted papers were given ?ve weeks to prepare the- nalversionsincluded in theseproceedings.Therevisedpaperswerenot reviewed again and their authors bear the responsibility for their content. Inadditiontothepapersincludedinthisvolume,theconferencealsofeatured aPosterandaRumpsession.Thelistofpresentedpostersappearsinthisvolume before the table of contents. Dan Bernstein served as the Chair of the Rump session. The conference also had the pleasure of hearing invited talks by Sha? Goldwasser and Phillip Rogaway.