This book constitutes the refereed proceedings of the 17th International Conference on Cryptology and Network Security, CANS 2018, held in Naples, Italy, in September/October 2018.The 26 full papers were carefully reviewed and selected from 79 submissions. The papers are organized in the following topical sections: privacy; Internet misbehavior and protection; malware; symmetric key cryptography; signatures; cryptanalysis; cryptographic primitives; and cryptographic protocols.