Role-based access control (RBAC) models are receiving increasing attention as a generalized approach to access control. Roles may be available to users at certain time periods, and unavailable at others. Moreover, there can be temporal dependencies among roles. To tackle such dynamic aspects, we introduce Temporal-RBAC (TRBAC), an extension of the RBAC model. TRBAC supports periodic role enabling and disabling—possibly with individual exceptions for particular users— and temporal dependencies among such actions, expressed by means of role triggers. Role trigger actions may be either immediately executed, or deferred by an explicitly specified amount of time. Enabling and disabling actions may be given a priority, which is used to solve conflicting actions. A formal semantics for the specification language is provided, and a polynomial safeness check is introduced to reject ambiguous or inconsistent specifications. Finally, a system implementing TRBAC on top of a conventional DBMS is presented.

Trust management (TM) is a promising approach for authorization and access control in distributed systems, based on signed distributed policy statements expressed in a policy language. Although several TM languages are semantically equivalent to subsets of Datalog, Datalog is not su#ciently expressive for fine-grained control of structured resources. We define the class of linearly decomposable unary constraint domains, prove that Datalog extended with constraints in any combination of such constraint domains is tractable, and show that permissions associated with structured resources fall into this class. We also present a concrete declarative TM language, RT 1 , based on constraint Datalog, and use constraint Datalog to analyze another TM system, KeyNote, which turns out to be less expressive than RT 1 in significant respects, yet less tractable in the worst case. Although constraint Datalog has been studied in the context of constraint databases, TM applications involve di#erent kinds of constraint domains and have different computational complexity requirements.

A policy describes the conditions under which an action is permitted or forbidden. We show that a fragment of (multi-sorted) first-order logic can be used to represent and reason about policies. Because we use first-order logic, policies have a clear syntax and semantics. We show that further restricting the fragment results in a language that is still quite expressive yet is also tractable. More precisely, questions about entailment, such as `May Alice access the file?', can be answered in time that is a low-order polynomial (indeed, almost linear in some cases), as can questions about the consistency of policy sets. We also give a brief overview of a prototype that we have built whose reasoning engine is based on the logic and whose interface is designed for non-logicians, allowing them to enter both policies and background information, such as `Alice is a student', and to ask questions about the policies.

We present a declarative authorization language that strikes a careful balance between syntactic and semantic simplicity, policy expressiveness, and execution efficiency. The syntax is close to natural language, and the semantics consists of just three deduction rules. The language can express many common policy idioms using constraints, controlled delegation, recursive predicates, and negated queries. We describe an execution strategy based on translation to Datalog with Constraints, and table-based resolution. We show that this execution strategy is sound, complete, and always terminates, despite recursion and negation, as long as simple syntactic conditions are met.

Access control is the process of mediating every request to resources and data maintained by a system and determining whether the request should be granted or denied. The access control decision is enforced by a mechanism implementing regulations established by a security policy. Different access control policies can be applied, corresponding to different criteria for defining what should, and what should not, be allowed, and, in some sense, to different definitions of what ensuring security means. In this chapter we investigate the basic concepts behind access control design and enforcement, and point out different security requirements that may need to be taken into consideration. We discuss several access control policies, and models formalizing them, that have been proposed in the literature or that are currently under investigation.

AbstractÐDigital Libraries (DLs) introduce several challenging requirements with respect to the formulation, specification, and enforcement of adequate data protection policies. Unlike conventional database environments, a DL environment typically is characterized by dynamic user population, often making accesses from remote locations, and by an extraordinarily large amount of multimedia information, stored in a variety of formats. Moreover, in a DL environment, access policies are often specified based on user qualifications and characteristics, rather than user identity (for example, a user can be given access to an R-rated video only if he/ she is older than 18 years). Another crucial requirement is the support for content-dependent authorizations on digital library objects (for example, all documents containing discussions on how to operate guns must be made available only to users who are 18 or older). Since traditional authorization models do not adequatly meet access control requirements typical to DLs, in this paper, we propose a content-based authorization model suitable for a DL environment. Specifically, the most innovative features of our authorization model are: 1) flexible specification of authorizations based on the qualifications and characteristics of users (including positive and negative), 2) both content-dependent and content-independent access control to digital library objects, and 3) varying granularity of authorization objects ranging from sets of library objects to specific portions of objects. Index TermsÐDigital libraries, access control, authorization. 1

We show how a range of role-based access control (RBAC) models may be usefully represented as constraint logic programs, executable logical specifications. The RBAC models that we define extend the “standard ” RBAC models that are described by Sandhu et al., and enable security administrators to define a range of access policies that may include features, like denials of access and temporal authorizations, that are often useful in practice, but which are not widely supported in existing access control models. Representing access policies as constraint logic programs makes it possible to support certain policy options, constraint checks and administrator queries that cannot be represented by using related methods (like logic programs). Representing an access control policy as a constraint logic program also enables access requests and constraint checks to be efficiently evaluated.

To my parents, for without them I wouldn’t have accomplished this milestone.- iii ACKNOWLEDGMENTS Acknowledgement is due to my advisor Prof. Arif Ghafoor, without whose support this thesis would not have seen the light of day. Also to be acknowledged are my committee members, Prof. Charlie Hu and Prof. Hong Tan, for their valuable input and encouragement. The guidance from Prof. Elisa Bertino at Università di Milano, Milano, Italy has been instrumental in the evolution of this work. Last but not the least, the research presented in this thesis has been partially supported by the National Science

The recent usage control model (UCON) is a foundation for next-generation access control models with distinguishing properties of decision continuity and attribute mutability. A usage control decision is determined by combining authorizations, obligations, and conditions, presented as UCONABC core models by Park and Sandhu. Based on these core aspects, we develop a formal model and logical specification of UCON with an extension of Lamport’s temporal logic of actions (TLA). The building blocks of this model include: (1) a set of sequences of system states based on the attributes of subjects, objects, and the system, (2) authorization predicates based on subject and object attributes, (3) usage control actions to update attributes and accessing status of a usage process, (4) obligation actions, and (5) condition predicates based on system attributes. A usage control policy is defined as a set of temporal logic formulas that are satisfied as the system state changes. A fixed set of scheme rules is defined to specify general UCON policies with the properties of soundness and completeness. We show the flexibility and expressive capability of this formal

A temporal RBAC (TRBAC) model has recently been proposed that addresses the temporal aspects of roles and trigger-based role enabling. However, it is limited to constraints on enabling of roles only. We propose a Generalized Temporal Role Based Access Control model (GTRBAC) that is capable of expressing a wider range of temporal constraints. GTRBAC is capable of expressing periodic as well as duration constraints on roles, user-role assignments and role-permission assignments. In GTRBAC, temporal constraints on role enablings and role activations can be separately specified. A user-activated role can further be restricted to various activation constraints such as cardinality constraint or maximum active duration constraint within a specified interval. The GTRBAC model extends the synta ctic structure of TRBAC model and its event and trigger expressions subsume those of TRBAC. Portions of this work were supported by the sponsors of the Center for Education and Role based access control (RBAC) models have generated great interest in the security community as a powerful and generalized approach to security [2, 13, 16, 18, 19]. In RBAC,