The two-volume set LNCS 15543 and 15544 constitutes revised selected papers of the 20th International Conference on Information Security and Cryptology, Inscrypt 2024, held in Kunming, China, during December 14–16, 2024. The 46 full papers presented in these proceedings were carefully reviewed and selected from 156 submissions. The papers were organized in the following topical sections: Part I : Big data and cloud security; Foundations of Cryptography; Implementation of Cryptosystems; Key Exchange; AI and Security; Security Analysis; Privacy-enhancing technologies; Watermarking. Part II : Public Key Cryptosystems; Security Protocols Analysis; Symmetric Cryptanalysis; Quantum and Post Quantum Cryptography.