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We develop a framework for specifying and reasoning about policies for sharing resources in coalitions, focussing here on a particular, common type of contract in which coalition members agree to make available some total amount of specified resource over a given time period. The main part of the framework is a policy language with two basic elements: 'obligations' (of a member enterprise to provide a total amount of resource over a given time period) express the coalition policy, and 'entitlements' (granted by an enterprise to other coalition members) express the local policies of the coalition members. We discuss the conditions under which a local policy can be said to be in compliance with, or meet, the obligations of a coalition policy, and the conditions under which an obligation, and by extension a contract, can be said to be violated or fulfilled.

We deal with an existing framework for updating privileges and creating management structures by means of authority certificates. These are used both to create access-level permissions and to delegate authority to other agents. Here we extend the framework to support a richer set of revocation schemes. The discussion of revocation follows an existing classification in the literature based on three separate dimensions: resilience, propagation, and dominance. The first one does not apply to this framework. The second one is specified straightforwardly. The third one can be encoded but raises a number of further questions for future investigation.

The rapid increase in the use of open distributed systems has given rise to a number of important issues for computer scientists, some of which concern the organisation of interactions between computers, between humans, and between humans and computers. For instance, such interactions are the focus of attention in access control policies (Abadi et al., 1993), and in cryptographic protocols (Burrows et al., 1990), both of which specify the actions that are to be performed by the participating agents.

What I am going to talk about is power and permission in security systems. This is work by me and my supervisor, Marek Sergot from Imperial College.