The 8-volume set LNCS 16245-16252 constitutes the refereed proceedings of the 31st International Conference on the Theory and Application of Cryptology and Information Security, ASIACRYPT 2025, which took place in Melbourne, Australia, during December 8–12, 2025.The 143 full papers included in the proceedings were carefully reviewed and selected from 533 submissions. These papers were organized into the following topical sections: Symmetric Cryptography; Cryptanalysis; Mathematic Aspects of Symmetric Cryptography; Secure Messaging; Formalization and Key Exchange; Data Structures; Blockchain; Secure Implementations; Design and Analysis of Implementations; Lattices; Post-Quantum Signatures; Groups and Group Actions; Isogenies; Multivariate Cryptanalysis and Code-based Crypto; Secure Computation; Succinct Proofs; Encryption with Advanced Features; Signatures with Advanced Features; Threshold Cryptography; Fully Homomorphic Encryption; Verifiable Computation; Pseudorandom Correlation; Secret Sharing; Quantum; and Foundations.