These are the proceedings of Eurocrypt 2004, the 23rd annual Eurocrypt conference. The conference was organized by members of the IBM Zurich Research Laboratory in cooperation with IACR, the International Association for Cryptologic Research.

The conference received a record number of 206 submissions, out of which the program committee selected 36 for presentation at the conference (three papers were withdrawn by the authors shortly after submission). These proceedings contain revised versions of the accepted papers. These revisions have not been checked for correctness, and the authors bear full responsibility for the contents of their papers.

The conference program also featured two invited talks. The first one was the 2004 IACR Distinguished Lecture held by Whitfield Diffie. The second invited talk was by Ivan Damgård who presented "Paradigms for Multiparty Computation." The traditional rump session with short informal talks on recent results was chaired by Arjen Lenstra.

The reviewing process was a challenging task, and many good submissions had to be rejected. Each paper was reviewed independently by at least three members of the program committee, and papers co-authored by a member of the program committee were reviewed by at least six (other) members. The individual reviewing phase was followed by profound and sometimes lively discussions about the papers, which contributed a lot to the quality of the final selection. Extensive comments were sent to the authors in most cases. At the end, the comments and electronic discussion notes filled more than 32'000 lines of text! We would like to thank the members of the program committee for their hard work over the course of several months; it was a pleasure for us to work with them and to benefit from their knowledge and insight. We are also very grateful to the external reviewers who contributed with their expertise to the selection process. Their work is highly appreciated.

The submission of all papers was done using the electronic submission software written by Chanathip Namprempre with modifications by Andre Adelsbach. During the review process, the program committee was mainly communicating using the web-based review software developed by Bart Preneel, Wim Moreau, and Joris Claessens. We would like to thank Roger Zimmermann for his help with installing and running the software locally, and for solving many other problems, not the least of which was the assembly of these proceedings.

The final decisions were made at a meeting in Rüschlikon at the IBM Zurich Research Laboratory. Helga Steimann helped us with the organization and also made sure there was enough coffee and food available so that we could concentrate on the papers and were not distracted by empty stomachs. Thanks a lot!

We are grateful to Endre Bangerter, Martin Hirt, Reto Strobl, and Roger Zimmermann for their help with the local arrangements of the conference. Eurocrypt 2004 was supported by the IBM Zurich Research Laboratory, Crypto AG, Omnisec, MediaCrypt, HP, Microsoft Research, and Swiss International Air Lines.

Our most important thanks go to our families for bearing with us through this busy period, for their support, and for their love.

Last but not least, we thank all the authors from all over the world who submitted papers. It is due to them and their work that the conference took place.

February 2004                           Christian Cachin and Jan Camenisch