This book constitutes the refereed proceedings of the 15th International Workshop on Security, IWSEC 2020, held in Fukui, Japan, in September 2020.*
The 15 regular papers and 1 short paper presented in this volume were carefully reviewed and selected from 47 submissions. They were organized in topical sections named: symmetric-key cryptography, malicious activity detection, multiparty computation, post quantum cryptography, privacy, pairing-based cryptography, and machine learning.
* The conference was held virtually due to the COVID-19 pandemic.

Symmetric-Key Cryptography 1.- Malicious Activity Detection 1.- Multiparty Computation.- Malicious Activity Detection 2.- Post Quantum Cryptography.- Symmetric-Key Cryptography 2.- Privacy.- Pairing-Based Cryptography.- Machine Learning.