Role-Based Access Control (RBAC) is supported directly or in a closely related form, by a number of products. This article presents a formalization of RBAC using graph transformations that is a graphical specification technique based on a generalization of classical string grammars to nonlinear structures. The proposed formalization provides an intuitive description for the manipulation of graph structures as they occur in information systems access control and a precise specification of static and dynamic consistency conditions on graphs and graph transformations. The formalism captures the RBAC models published in the literature, and also allows a uniform treatment of user roles and administrative roles, and a detailed analysis of the decentralization of administrative roles.

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Graph-based specification formalisms for access control (AC) policies combine the advantages of an intuitive visual framework with a rigorous semantical foundation that allows the detailed comparison of different policy models. A security policy framework specifies a set of (constructive) rules to build the system states and sets of positive and negative (declarative) constraints to specify wanted and unwanted substates. Several models for AC (e.g. role-based, lattice-based or an access control list) can be specified in this framework. The framework is used for an accurate analysis of the interaction between policies and of the behavior of their integration with respect to the problem of inconsistent policies. Using formal properties of graph transformations, it is possible to systematically detect inconsistencies between constraints, between rules and between a rule and a constraint and lay the foundation for their resolutions. (C) 2004 Elsevier Inc. All rights reserved

Models of Access Control Policies specified with graphs and graph transformation rules combine an intuitive visual representation with solid semantical foundations. While the expressive power of graph transformations leads in general to undecidable models, we prove that it is possible, with reasonable restrictions on the form of the rules, to obtain access control models where safety is decidable. The restrictions introduced are minimal in that no deletion and addition of a graph structure are allowed in the same modification step. We then illustrate our result with two examples: a graph based DAC model and a simplified decentralized RBAC model.

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