Book excerpt: This book constitutes the refereed proceedings of the 24th IFIP TC 11 International Information Security Conference, SEC 2009, held in Pafos, Cyprus, in May 2009. The 38 revised full papers presented were carefully reviewed and selected from 176 submissions. The papers are organized in topical sections on identification and authentication, threats and attacks, applications of cryptography and information hiding, trusted computing, security policies, validation, verification and evaluation, privacy protection and security assessment, role mining and content protection, security protocols, access control, and internet and Web applications security.