Affiliations: Department of Computer Science, University of California at Davis, Davis, CA 95616-8562, USA
Note: [*] Portions of this work were supported by grant NAG2-480 from the National Aeronautics and Space Administration to Dartmouth College, were done at Dartmouth College, and stem from the author's Ph.D. dissertation. A preliminary version of this paper was presented at the First Computer Security Foundations Workshop in Franconia, NH (1988).
Abstract: Questions of information flow are in many ways more important than questions of access control, because the goal of many security policies is to thwart the unauthorized release of information, not merely the illicit obtaining of access rights to that information. The Take-Grant Protection Model is an excellent theoretical tool for examining such issues because conditions necessary and sufficient for information to flow between two objects, and for rights to objects to be obtained or stolen, are known. In this paper we extend these results by examining the question of information flow from an object the owner of which is unwilling to release that information. Necessary and sufficient conditions for such “theft of information” to occur are derived. To emphasize the usefulness of these results, the security policies of complete isolation, transfer of rights with the cooperation of an owner, and transfer of information (but not rights) with the cooperation of the owner are presented; the last is used to model a subject guarding a resource.
