This book constitutes the refereed proceedings of the 16th International Workshop on Security, IWSEC 2021, held in Tokyo, Japan in September 2021. The conference was held virtually due to COVID-19 pandemic. The 14 regular papers and 3 short paper presented in this volume were carefully reviewed and selected from 37 submissions. They were organized in topical sections named: Lattice-Based Cryptography; System Security; Multiparty Computation; Machine Learning and Security; Post-quantum Cryptography; Symmetric-key Cryptography; Game Theory and Security.

This book constitutes the refereed proceedings of the 16th International Workshop on Security, IWSEC 2021, held in Tokyo, Japan in September 2021. The conference was held virtually due to COVID-19 pandemic. The 14 regular papers and 3 short paper presented in this volume were carefully reviewed and selected from 37 submissions. They were organized in topical sections named: Lattice-Based Cryptography; System Security; Multiparty Computation; Machine Learning and Security; Post-quantum Cryptography; Symmetric-key Cryptography; Game Theory and Security.