This three-set volume LNCS 16217-16219 constitutes the refereed proceedings of 27th International Conference on Information and Communications Security, ICICS 2025, held in Nanjing, China, during October 29–31, 2025.The 91 full papers presented in this book were carefully selected and reviewed from 357 submissions. The papers are organized in the following topical sections:Part I: Cryptography; Post-quantum Cryptography; Anonymity and Privacy; Authentication and Authorization.Part II: Blockchain and Cryptocurrencies, System and Network Security, Security and Privacy of AI, Machine Learning for Security. Part III: Attack and Defense; Vulnerability Analysis; Anomaly Detection; Traffic Classification; Steganography and Watermarking.