Authorization systems today are increasingly complex. They span domains of administration, rely on many different authentication sources, and manage permissions that can be as complex as the system itself. Worse still, while there are many standards that define authentication mechanisms, the standards that address authorization are less well defined and tend to work only within homogeneous systems. This paper presents XACML, a standard access control language, as one component of a distributed and inter-operable authorization framework. Several emerging systems which incorporate XACML are discussed. These discussions illustrate how authorization can be deployed in distributed, decentralized systems. Finally, some new and future topics are presented to show where this work is heading and how it will help connect the general components of an authorization system.

In this paper, we first present a private distributed scalar product protocol that can be used for obtaining trust values from private recommendations. Our protocol allows Alice to infer the trustworthiness of Bob based on what Alice's friends think about Bob and Alice's confidence in her fiiends. In addition, the private information of Alice and her fiiends are not revealed during the computation. We also propose a credential-based trust model where the trustworthiness of a user is computed based on his or her affiliations and role assignments. The trust model is simple to compute, yet it is scalable as it classifies large groups of users.

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