Information security is critical to economies, communities, governments, social networking and safety of citizens. With the advent of the Internet and the rapid development of Internet-based application such as e-commerce, e-government and social network systems, it is paramount that mechanisms are put in place to ensure the security of information stored and exchanged in such a worldwide and open distributed system. This book presents a unified compositional formal framework for the specification of the functional, temporal and security requirements of systems. This provides an effective way of integrating security concerns into the system requirements and to address them early in the system development life cycle so that security holes can be detected and fixed timely. The book contains a great deal of material for students, lecturers, researchers and practitioners in the field of information security.