This book constitutes the refereed proceedings of the First International Conference on Applied Cryptography and Network Security, ACNS 2003, held in Kunming, China, in October 2003. The 32 revised full papers presented were carefully reviewed and selected from a total of 191 submissions. The papers are organized in topical sections on cryptographic applications, intrusion detection, cryptographic algorithms, digital signatures, security modeling, Web security, security protocols, cryptanalysis, key management, and efficient implementations.