Book excerpt: This book constitutes selected papers from the 24th International Conference on Information Security and Cryptology, ICISC 2021, held in Seoul, South Korea, in December 2021. The total of 23 papers presented in this volume were carefully reviewed and selected from 63 submissions. The papers are arranged by topic: Cryptographic Protocol in Quantum Computer Age; Security Analysis of Hash Algorithm; Security analysis of Symmetric Key Encryption Algorithm; Fault and Side-Channel Attack; Constructions and Designs; Quantum Circuit; Efficient Implementation. 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.