This book constitutes the refereed proceedings of the 12th IMA International Conference on Cryptography and Coding, held in Cirencester, UK in December 2009.

The 26 revised full papers presented together with 3 invited contributions were carefully reviewed and selected from 53 submissions. The papers are organized in topical sections on coding theory, symmetric cryptography, security protocols, asymmetric cryptography, Boolean functions and side channels and implementations.