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 47 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.