This book constitutes selected papers from the 23rd International Conference on Information Security and Cryptology, ICISC 2020, held in Seoul, South Korea, in December 2020. Due to the COVID-19, the confere was held online. The total of 15 papers presented in this volume were carefully reviewed and selected from 51 submissions. The aim of this conference was to provide an international forum for the latest results of research, development, and applications within the field of information security and cryptology.