This book constitutes the refereed proceedings of the 11th International Workshop on Security, IWSEC 2016, held in Tokyo, Japan, in September 2016. The 15 regular papers and 4 short papers presented in this volume were carefully reviewed and selected from 53 submissions. They were organized in topical sections named: system security; searchable encryption; cryptanalysis; permutation and symmetric encryption; privacy preserving; hardware security; post-quantum cryptography; and paring computation.