These proceedings contain the papers selected for presentation at the 4th Wo- shop on Information Security Theory and Practice (WISTP 2010), held during April 12-14, 2010 in Passau, Germany. In response to the call for papers, 69 papers were submitted to the wo- shop. These papers were evaluated on the basis of their signi?cance, novelty, and technicalquality. Eachpaper was reviewedby four members of the Program Committee. Reviewing was double-blind meaning that the Program Committee was not able to see the names and a?liations of the authors, and the authors were not told which committee members reviewed which papers. The Program Committee meeting was held electronically, holding intensive discussions over a periodoftwo weeks.Of the papers submitted, 20 full papersand 10shortpapers were selected for presentation at the workshop. This workshop was sponsored by Vodaphone, who also provided a best - per award. We would like to thank this organization for their support, which helped make this workshop possible. Their continued support helps to reduce registration fees and make WISTP a continuing success. WISTP 2010 was also organized in cooperation with the International - sociation for Cryptologic Research (IACR), the IFIP WG 11.2 Pervasive S- tems Security, and ACM SIGSAC. Their support has signi?cantly contributed to raising the pro?le of WISTP, which is re?ected in the number of high-quality submissions that we received.