Epistemology of Information Flow in the Multilevel Security of Probabilistic Systems

We set out a modal logic for reasoning about multilevel security of probabilistic systems. This logic includes modalities for time, probability, knowledge, and permitted-knowledge. Making use of the Halpern-Tuttle framework for reasoning about knowledge and probability, we give a semantics for our logic and prove that it is sound. We give two syntactic de nitions of perfect multilevel security and show that their semantic interpretations are equivalent to two earlier, independently motivated characterizations. We also discuss the relation between these characterizations of security and between their usefulness in security analysis. A portion of this work was performed while the rst author was at the Naval Research Laboratory in Washington, DC. J.W. Gray, III and P.F. Syverson. Epistemology of Information Flow in the Multilevel Security of Probabilistic Systems. NRL Memo Report 5540{95-7733, May 12, 1995 X covert receivers R1