This book constitutes the thoroughly refereed post-conference proceedings of the 18th International Conference on Information Security Applications, WISA 2017, held on Jeju Island, Korea, in August 2017. The 12 revised full papers and 15 short papers presented in this volume were carefully reviewed and selected from 53 submissions. The papers are organized in topical sections such as attack and defense; theory in security; web security and emerging technologies; systems security and authentication; crypto protocols; and attack detections and legal aspects.