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.