The three-volume set constitutes revised selected papers of the 21st International Conference on Information Security and Cryptology, Inscrypt 2025, held in Xi'an, China, on October 19, 2025.The 79 full papers presented in these proceedings were carefully reviewed and selected from 315 submissions. The papers were organized in the following topical sections: Part I :  Post-Quantum Cryptography; Functional Encryption;  Cryptanalysis and Implementations I; Cryptanalysis and Implementations II. Part II : Secure Multi-party Computation; Anomaly Detection Methodologies & Models;  Network Security & Traffic Analysis. Part III : Privacy Preserving/Enhancing Technologies;  AI and Security I; AI and Security II.