This book constitutes the refereed proceedings of the 5th International Conference on Applied Cryptography and Network Security, ACNS 2007, held in Zhuhai, China, June 2007. The 31 revised full papers cover signature schemes, computer and network security, cryptanalysis, group-oriented security, cryptographic protocols, anonymous authentication, identity-based cryptography, and security in wireless, ad-hoc, and peer-to-peer networks.