A Logic of Access Control

The e ectiveness of an access control mechanism in implementing a security policy in a centralised operating system is often weakened because of the large number of possible access rights involved, informal speci cation of security policy and a lack of tools for assisting systems administrators. Herein we present a logical foundation for automated tools that assist in determining which access rights should be granted by reasoning about the e ects of an access control mechanism on the computations performed by an operating system. We demonstrate the practicality and utility of our logical approach by showing how it allows us to construct a deductive database capable of answering questions about the security of two real-world operating systems. We illustrate the application of our techniques by presenting the results of an experiment designed to assess how accurately the con guration of an access control mechanism implements a given security policy.