This book constitutes the thoroughly refereed post-workshop proceedings of the 12th International Workshop on Information Security Applications, WISA 2011, held in Jeju Island, Korea, in August 2011. The 21 revised full papers presented were carefully reviewed and selected from 74 submissions. The workshop serves as a forum for new results from the academic research community as well as from the industry; the papers are focusing on all technical and practical aspects of cryptographic and non-cryptographic security applications.