Experimenting with quantitative evaluation tools for monitoring operational security

This paper presents the results of an experiment in security evaluation. Th e system is modeled as a privilege graph that exhibits its security vulnera bilities. Quantitative measures that estimate the effort an attacker might expend to exploit these Vulnerabilities to defeat the system security objec tives are proposed. A set of tools has been developed to compute such measu res and has been used in an experiment to monitor a large real system for n early two years. The experimental results are presented and the validity of the measures is discussed. Finally, the practical usefulness of such tools for operational security monitoring is shown and a comparison with other e xisting approaches is given.