This book constitutes the refereed proceedings of the 6th International Conference on Information Security, ISC 2003, held in Bristol, UK in October 2003. The 31 revised full papers presented together with 2 invited papers were carefully reviewed and selected from 133 submissions. The papers are organized in topical sections on network security, public key algorithms, cryptographic protocols, protocol attacks, attacks on public key cryptosystems, block ciphers, authorization, water marking, software security, and codes and related issues.