This book constitutes the refereed proceedings of the Second International Conference on Applied Cryptography and Network Security, ACNS 2004, held in Yellow Mountain, China, in June 2004. The 36 revised full papers presented were carefully reviewed and selected from 297 submissions. The papers are organized in topical sections on security and storage, provably secure constructions, Internet security, digital signatures, security modeling, authenticated key exchange, security of deployed systems, cryptosystems design and analysis, cryptographic protocols, side channels and protocol analysis, intrusion detection and DoS, and cryptographic algorithms.