Document Type

Technical Report

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Technical Report Number



(Revised 5/90). 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 sufficienct for information to flow between tow objects, and for rights to object to be obtained or stolen, are known. In this paper we extend these results by examinig 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, and bounds on the number of subjects that must take action for the theft to occur are presented. 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 usedto model a simple reference monitor guarding a resource.