Abstract
Today, many applications require users from one organization to access data belonging to organizations. While traditional solutions offered for the federated and mediated databases facilitate this by sharing metadata, this may not be acceptable for certain organizations due to privacy concerns. In this paper, we propose a novel solution -- Privacy-preserving Access Control Toolkit (PACT) -- that enables privacy-preserving secure semantic access control and allows sharing of data among heterogeneous databases without having to share metadata. PACT uses encrypted ontologies, encrypted ontology-mapping tables and conversion functions, encrypted role hierarchies and encrypted queries. The encrypted results of queries are sent directly from the responding system to the requesting system, bypassing the mediator to further improve the security of the system. PACT provides semantic access control using ontologies and semantically expanded authorization tables at the mediator. One of the distinguishing features of the PACT is that it requires very little changes to underlying databases. Despite using encrypted queries and encrypted mediation, we demonstrate that PACT provides acceptable performance.