This book constitutes the refereed proceedings of the 26th International Conference on Information Security and Cryptology on Information Security and Cryptology - ICISC 2023, held in Seoul, South Korea, during November 29-December 1, 2023 The 31 full papers included in this book were carefully reviewed and selected from 78 submissions. They were organized in topical sections as follows: Part I: Cryptanalysis and Quantum Cryptanalysis; Side Channel Attack; Signature Schemes. Part II: Cyber Security; Applied Cryptography; and Korean Post Quantum Cryptography.