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, 2023The 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.