Towards an Efficient and Language-Agnostic Compliance Checker for Trust Negotiation Systems
To ensure that a trust negotiation succeeds whenever possible, authorization policy compliance checkers must be able to find all minimal sets of their owners' credentials that can be used to satisfy a given policy. If all of these sets can be found efficiently prior to choosing which set should be disclosed, many strategic benefits can also be realized. Unfortunately, solving this problem using existing compliance checkers is too inefficient to be useful in practice. Specifically, the overheads of finding all satisfying sets using existing approaches have been shown to rapidly grow exponentially in the size of the union of all satisfying sets of credentials for the policy, even after optimizations have been made to prune the search space for potential satisfying sets. In this paper, we describe the Clouseau compliance checker. Clouseau leverages efficient pattern-matching algorithms to find all satisfying sets of credentials for a given policy in time that grows as O(NA), where N is the number of satisfying sets for the policy and A is the average size of each satisfying set. We describe the design and implementation of the Clouseau compliance checker, evaluate its performance as the number and size of satisfying sets for a given policy varies, and show that it vastly outperforms existing approaches to finding all satisfying sets of credentials. We then present a method for automatically compiling RT policies into a format suitable for analysis by Clouseau and prove the correctness and completeness of this compilation procedure.
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