This book constitutes the refereed proceedings of the 5th International Conference on Cryptology and Network Security, CANS 2006, held in Suzhou, China, December 2006. The 26 revised full papers and 2 invited papers cover encryption, authentication and signatures, proxy signatures, cryptanalysis, implementation, steganalysis and watermarking, boolean functions and stream ciphers, intrusion detection, and disponibility and reliability.