Policy models for compliance checking and xml access control

The focus of this work is to develop techniques that can be used to enforce access control with flexible granularity and check compliance of implemented security (low-level) policies to an organization's security policy (high-level). Ensuring compliance is a desired goal from the management perspective as it prevents disruptions in functioning of organizations. This work presents a compliance checking framework and methods to verify whether an implemented, low-level policy is compliant to a high-level policy. The compliance checking framework is based on organizational and security metadata to support refinement of high-level security policy to implementation specific instances. This work uses the results of refinement calculus to express valid refinement patterns and their properties. Intuitively, a low-level policy is compliant to a high-level policy if there is a valid refinement path from the high-level policy to the low-level policy. Inflexible security granularity of the existing access control mechanisms are often a hindrance in achieving compliance goals, therefore this work focuses on development of access control techniques with flexible granularity. In particular, this work presents techniques to support association-level access control for XML. Intuitively, an association security object is an XML subtree that is not allowed to be accessed by a user, while all of its proper subtrees are permitted separately. This work presents a query-filtering technique that evaluates XML queries to detect disclosure of association-level security objects. A bottom-up tree automaton is used to model-security objects. Intuitively a query Q discloses a security object o if and only if the (tree) automaton corresponding to o accepts Q. The schema-level method presented in this work detects all possible disclosures, i.e., it is complete. This work also presents empirical results from the implementation of node and association level access control in the native XML database—eXist. The proposed model performs security checks at three stages: query pre-processing, actual query evaluation and post-query evaluation. My results from performance analysis tests show that the access control model is scalable and introduces a constant overhead regardless of the size of XML database.