Verification and change-impact analysis of access-control policies

Sensitive data are increasingly available on-line through the Web and other distributed protocols. This heightens the need to carefully control access to data. Control means not only preventing the leakage of data but also permitting access to necessary information. Indeed, the same datum is often treated differently depending on context. System designers create policies to express conditions on the access to data. To reduce source clutter and improve maintenance, developers increasingly use domain-specific, declarative languages to express these policies. In turn, administrators need to analyze policies relative to properties, and to understand the effect of policy changes even in the absence of properties. This paper presents Margrave, a software suite for analyzing role-based access-control policies. Margrave includes a verifier that analyzes policies written in the XACML language, translating them into a form of decision-diagram to answer queries. It also provides semantic differencing information between versions of policies. We have implemented these techniques and applied them to policies from a working software application.