The present volume contains the proceedings of the 5th International Workshop on Formal Aspects in Security and Trust (FAST 2008), held in Malaga, Spain, October 9-10, 2008. FAST is an event a?liated with the 13th European Sym- sium on Research in Computer Security (ESORICS 2008). FAST 2008 was held under the auspices of the IFIP WG 1.7 on Foundations of Security Analysis and Design. The 5th International Workshop on Formal Aspects in Security and Trust (FAST 2008) aimed at continuing the successful e?ort of the previous three FAST workshop editions for fostering the cooperation among researchers in the areas of security and trust. As computing and network infrastructures become increasingly pervasive, and as they carry increasing economic activity, society needs well-matched security and trust mechanisms. These interactions incre- ingly span several enterprises and involve loosely structured communities of - dividuals. Participants in these activities must control interactions with their partners based on trust policies and business logic. Trust-based decisions - fectively determine the security goals for shared information and for access to sensitive or valuable resources. FAST sought for original papers focusing on formal aspects in: security and trust policy models; security protocol design and analysis; formal models of trustand reputation;logicsfor security andtrust;distributed trust management systems;trust-basedreasoning;digitalassetsprotection;dataprotection;privacy and ID issues; information ?ow analysis; language-based security; security and trust aspects in ubiquitous computing; validation/analysis tools; Web service security/trust/privacy; GRID security; security risk assessment; case studies.