This book constitutes the refereed proceedings of the 12th Australasian Conference on Information Security and Privacy, ACISP 2007, held in Townsville, Australia in July 2007. The 33 revised full papers presented were carefully reviewed and selected from 132 submissions. The papers are organized in topical sections on stream ciphers, hashing, biometrics, secret sharing, cryptanalysis, public key cryptography, authentication, e-commerce, and security.