This book constitutes the refereed proceedings of the Third International Workshop on Security, IWSEC 2008, held in Kagawa, Japan, in November 2008. The 18 revised full papers presented together with 1 invited talk were carefully reviewed and selected from 94 submissions. The papers are organized in topical sections on cryptography, signature and signcryption, software security, privacy protection and contents protection, authentication and access control, as well as implementation.