This book constitutes the refereed proceedings of the 12th International Conference on Cryptology and Network Security, CANS 2013, held in Paraty, Brazil, in November 2013. The 18 revised full papers presented together with four invited talks were carefully reviewed and selected from 57 submissions. The papers are organized in topical sections on cryptanalysis, zero-knowledge protocols, distributed protocols, network security and applications, advanced cryptographic primitives, and verifiable computation.