Safety and consistency in policy-based authorization systems

In trust negotiation and other distributed proving systems, networked entities cooperate to form proofs that are justi?ed by collections of certi?ed attributes. These attributes may be obtained through interactions with any number of external entities and are collected and validated over an extended period of time. Though these collections of credentials in some ways resemble partial system snapshots,these systems currently lack the notion of a consistent global state in which the satisfaction of authorization policies should be checked. In this paper, we argue that unlike the notions of consistency studied in other areas of distributed computing, the level of consistency required during policy evaluation is predicated solely upon the security requirements of the policy evaluator. As such,there is little incentive for entities to participate in complicated consistency preservation schemes like those used in distributed computing,distributed databases, and distributed shared memory. We go on to show that the most intuitive notion of consistency fails to provide basic safety guarantees under certain circumstances and then propose several more refined notions of consistency which provide stronger safety guarantees. We provide algorithms that allow each of these re ?ned notions of consistency to be attained in practice with minimal overheads.