Advances in Information and Computer Security Security and Cryptology : Springer : 9783642048456 : 3642048455 : 05 Oct 2009 : The Fourth International Workshop on Security (IWSEC 2009) was held at Toyama International Conference Center, Toyama, Japan, October 28?30, 2009. The workshop was co-organized by CSEC, a special interest group on computer security of the IPSJ (Information Processing Society of Japan) and ISEC, a technical group on information security of IEICE (The Institute of Electronics, Information and Communication Engineers). The excellent Local Organizing Committee was led by the IWSEC 2009 General Co-chairs, Kazuo Takaragi and Hiroaki Kikuchi. IWSEC2009received46papersubmissionsfromallovertheworld.Wewould like to thank all the authors who submitted papers. Eachpaper was reviewedby at least three reviewers. In addition to the Program Committee members, many externalreviewersjoinedthereviewprocessintheirparticularareasofexpertise. We were fortunate to have this energetic