Dynamic Enforcement of Knowledge-based Security Policies
MARYLAND UNIV COLLEGE PARK DEPT OF COMPUTER SCIENCE
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This paper explores the idea of knowledge-based security policies, which are used to decide whether to answer queries over secret data based on an estimation of the queriers possibly increased knowledge given the results. Limiting knowledge is the goal of existing information release policies that employ mechanisms such as noising, anonymization and redaction. Knowledge-based policies are more general they increase flexibility by not fixing the means to restrict information flow. We enforce a knowledge-based policy by explicitly tracking a model of a queriers belief about secret data, represented as a probability distribution, and denying any query that could increase knowledge above a given threshold. We implement query analysis and belief tracking via abstract interpretation using a novel probabilistic polyhedral domain whose design permits trading off precision with performance while ensuring estimates of a queriers knowledge are sound. Experiments with our implementation show that several useful queries can be handled efficiently, and performance scales far better than would more standard implementations of probabilistic computation based on sampling.
- Computer Programming and Software