Constitutes the refereed post-proceedings of the Fourth International Workshop on Formal Aspects in Security and Trust, FAST 2006, held in Hamilton, Ontario, Canada, August 26-27, 2006. This book includes papers that focus on formal aspects in security and trust policy models, security protocol design and analysis, and trust-based reasoning.

Strategic Games on Defense Trees.- Timed Calculus of Cryptographic Communication.- A Semantic Paradigm for Component-Based Specification Integrating a Notion of Security Risk.- Game-Based Criterion Partition Applied to Computational Soundness of Adaptive Security.- Measuring Anonymity with Relative Entropy.- Formalizing and Analyzing Sender Invariance.- From Simulations to Theorems: A Position Paper on Research in the Field of Computational Trust.- A Tool for the Synthesis of Controller Programs.- Where Can an Insider Attack?.- Maintaining Information Flow Security Under Refinement and Transformation.- A Classification of Delegation Schemes for Attribute Authority.- Program Partitioning Using Dynamic Trust Models.- Locality-Based Security Policies.- A Theorem-Proving Approach to Verification of Fair Non-repudiation Protocols.- A Formal Specification of the MIDP 2.0 Security Model.- A Comparison of Semantic Models for Noninterference.- Hiding Information in Multi Level Security Systems.- A New Trust Model Based on Advanced D-S Evidence Theory for P2P Networks.