This book constitutes the refereed proceedings of the 18th International Conference on Cryptology and Network Security, CANS 2019, held in Fuzhou, China, in October 2019. The 21 full papers and 8 short papers were carefully reviewed and selected from 55 submissions. The papers focus on topics such as homomorphic encryption; SIKE and Hash; lattice and post-quantum cryptography; searchable encryption; blockchains, cloud security; secret sharing and interval test, LWE; encryption, data aggregation, and revocation; and signature, ML, payment, and factorization.