These proceedings contain the papers selected for presentation at the 23rd Inter- tional Information Security Conference (SEC 2008), co-located with IFIP World Computer Congress (WCC 2008), September 8-10, 2008 in Milan, Italy. In - sponse to the call for papers, 143 papers were submitted to the conference. All - pers were evaluated on the basis of their signi?cance, novelty, and technical quality, and reviewed by at least three members of the program committee. Reviewing was blind meaning that the authors were not told which committee members reviewed which papers. The program committee meeting was held electronically, holding - tensive discussion over a period of three weeks. Of the papers submitted, 42 full papers and 11 short papers were selected for presentation at the conference. A conference like this just does not happen; it depends on the volunteer efforts of a host of individuals. There is a long list of people who volunteered their time and energy to put together the conference and who deserve acknowledgment. We thank all members of the program committee and the external reviewers for their hard work in the paper evaluation. Due to the large number of submissions, p- gram committee members were required to complete their reviews in a short time frame. We are especially thankful to them for the commitment they showed with their active participation in the electronic discussion.