21 - Security models

Abstract

Security models are formal descriptions of security policies or abstract models of access control systems. They are a starting point when designing security systems and provide a framework for developing theories of access control. The chapter presents a survey of important security models and fundamental theorems about access control. The development process proposed in the chapter starts from a model of the security requirements that serves as a yardstick for analyzing top-level specification of the system to be built. The top-level specification is refined and a series of lower-level specifications finally leads to the actual implementation of the system. Consistency among the different levels of specifications may be checked informally or by formal means for the highest degree of assurance. In the context of such a design process, the security model is a formal description of the security policy the system should enforce. This definition of security models is frequently found in the security literature.