This book constitutes the proceedings of the 18th International Conference on Provable and Practical Security, ProvSec 2024, which took place in Gold Coast, QLD, Australia, during September 25-27, 2024. The 26 full papers and 8 short papers presented were thoroughly reviewed and selected from the 79 submissions. The papers are organized in the following topical sections: Part I: Multi-Party Computation; Searchable Encryption; Encryption and Signature. Part II: Tight Security; Quantum-Safe Cryptography; Distributed System and Blockchain Security; and Key Exchange and Privacy