This book constitutes the thoroughly refereed post-proceedings of the 4th International Workshop on Information Security Applications, WISA 2003, held on Jeju Island, Korea, in August 2003. The 36 revised full papers were carefully reviewed and selected from 200 submissions. The papers are organized in topical sections on network security, mobile security; intrusion detection; Internet security; secure software, hardware, and systems; e-commerce security; digital rights management; biometrics and human interfaces; public key cryptography and key management; and applied cryptography.