The Fifth International Workshop on Security (IWSEC 2010) was held at Kobe InternationalConferenceCenter,Kobe,Japan,November22–24,2010. Thewo- shop was co-organized by CSEC, a special interest group concerned with the computer security of the Information Processing Society of Japan (IPSJ) and ISEC,atechnicalgroupconcernedwiththe informationsecurityofTheInstitute of Electronics, Information and Communication Engineers (IEICE). The exc- lentLocalOrganizingCommitteewasledbytheIWSEC2010GeneralCo-chairs, Hiroaki Kikuchi and Toru Fujiwara. This year IWSEC 2010 had three tracks, the Foundations of Security (Track I), Security in Networks and Ubiquitous Computing Systems (Track II), and Security in Real Life Applications (Track III), and the review and selection processes for these tracks were independent of each other. We received 75 paper submissions including 44 submissions for Track I, 20 submissions for Track II, and 11 submissions for Track III. We would like to thank all the authors who submitted papers. Each paper was reviewed by at least three reviewers. In - dition to the Program Committee members, many external reviewers joined the review process from their particular areas of expertise. We were fortunate to have this energetic team of experts, and are grateful to all of them for their hard work. This hard work included very active discussions; the discussion phase was almost as long as the initial individual reviewing. The review and discussions weresupportedbyaveryniceWeb-basedsystem,iChair. Wewouldliketothank its developers. Following the review phases, 22 papers including 13 papers for Track I, 6 papers for Track II, and 3 papers for Track III were accepted for publication in this volume of Advances in Information and Computer Security.