This volume constitutes the refereed proceedings of the 6th IFIP WG 11.2 International Workshop on Information Security Theory and Practice: Security, Privacy and Trust in Computing Systems and Ambient Intelligent Ecosystems, WISTP 2012, held in Egham, UK, in June 2012. The 9 revised full papers and 8 short papers presented together with three keynote speeches were carefully reviewed and selected from numerous submissions. They are organized in topical sections on protocols, privacy, policy and access control, multi-party computation, cryptography, and mobile security.