The second International Conference on Applied Cryptography and Network Security (ACNS 2004) was sponsored and organized by ICISA (the International Communications and Information Security Association). It was held in Yellow Mountain, China, June 8–11, 2004. The conference proceedings, representing papers from the academic track, are published in this volume of the Lecture Notes in Computer Science (LNCS) of Springer-Verlag. The area of research that ACNS covers has been gaining importance in recent years due to the development of the Internet, which, in turn, implies global exposure of computing resources. Many fields of research were covered by the program of this track, presented in this proceedings volume. We feel that the papers herein indeed reffect the state of the art in security and cryptography research, worldwide. The program committee of the conference received a total of 297 submissions from all over the world, of which 36 submissions were selected for presentation during the academic track. In addition to this track, the conference also hosted a technical/industrial track of presentations that were carefully selected as well. All submissions were reviewed by experts in the relevant areas.