ABAM: An Attribute-Based Access Matrix Model

In traditional access control models like mandatory access control (MAC), discretionary access control (DAC), and role-based access control (RBAC), authorization decisions are determined according to the identities of subjects and objects, which are authenticated by a system completely. Recent access control practices, such as digital rights management (DRM), trust management, and usage control, require flexible authorization policies. In such systems, a subject may be only partially authenticated according to one or more attributes. Authorization policies are specified with subject and object attribute values. In this paper we propose an attribute-based access matrix model, named ABAM, which extends the original access matrix model. We show that ABAM enhances the expressive power of the access matrix model by supporting attribute-based authorizations and dynamic permission propagations. Specifically, ABAM is comprehensive enough to encompass traditional access control models as well as some usage control features. As expressive power and safety are two fundamental but conflictive objectives of an access control model, we study the safety property of ABAM and conclude that the safety problem is decidable for a restricted case where attribute relationship graph allows no cycles containing creating-attribute tuples. The restricted case is shown to sustain good expressive power to model practical systems.