This book constitutes the refereed proceedings of the 12th International Conference on Information and Communications Security, ICICS 2010, held in Barcelona, Spain, in December 2010. The 31 revised full papers presented together with an invited talk were carefully reviewed and selected from 135 submissions. The papers are organized in topical sections on access control, public key cryptography and cryptanalysis, security in distributed and mobile systems, cryptanalysis, authentication, fair exchange protocols, anonymity and privacy, software security, proxy cryptosystems, and intrusion detection systems.