This book constitutes the refereed proceedings of the 5th International Workshop on Information Security Applications, WISA 2004, held in Jeju Island, Korea in August 2004.The 36 revised full papers presented were carefully selected during two rounds of reviewing and improvement from 169 submissions. The papers are organized in topical sections on network and computer security, public key systems, intrusion detection, watermarking and anti-spamming, digital rights management, e-commerce security, efficient implementations, anonymous communication, and side channel attacks.