This book constitutes the refereed proceedings of the 6th International Conference on Information and Communications Security, ICICS 2004, held in Malaga, Spain in October 2004. The 42 revised full papers presented were carefully reviewed and selected from 245 submissions. The papers address a broad range of topics in information and communication security including digital signatures, group signature schemes, e-commerce, digital payment systems, cryptographic attacks, mobile networking, authentication, channel analysis, power-analysis attacks, mobile agent security, broadcast encryption, AES, security analysis, XTR, access control, and intrusion detection.