Automata-based approach to design and analyze security policies

Information systems must be controlled by security policies to protect them from undue accesses. Security policies are often designed by rules expressed using informal text, which implies ambiguities and inconsistencies in security rules. Our objective in this paper is to develop a formal approach to design and analyze security policies. We propose a procedure that synthesizes an automaton which implements a given security policy. Our automata-based approach can be a common basis to analyze several aspects of security policies. We use our automata-based approach to develop three analysis procedures to: verify completeness of a security policy, detect anomalies in a security policy, and detect functional discrepancies between several implementations of a security policy. We illustrate our approach using examples of security policies for a firewall.