This book constitutes the refereed proceedings of the 9th Australasian Conference on Information Security and Privacy, ACISP 2004, held in Sydney, Australia in July 2004.The 41 revised full papers presented were carefully reviewed and selected from 195 submissions. The papers are organized in topical sections on broadcast encryption and traitor tracing, private information retrieval and oblivious transfer, trust and secret sharing, cryptanalysis, digital signatures, cryptosystems, fast computation, mobile agents security, protocols, security management, and access control and authorization.