In this article we show how to model a range of notions in the context of delegation and revocation applied to security scenarios. We demonstrate how a range of delegation-revocation models and policies may be represented in pictorial form and formally represented in terms of reactive Kripke models and a first-order policy specification language. We translate first-order representations of our reactive Kripke models into an equivalent Answer Set Programming form that enables users to apply flexibly well-defined definitions of predicates to represent their requirements in terms of delegation-revocation policy specification.

We show how core concepts in access control can be represented in axiomatic terms and how multiple access control models and policies can be uniformly represented as particular logical theories in the axiom system that we introduce. Authorization policies are represented in our framework by using a form of answer set programming. We describe the motivations for our approach and we consider how properties of policies can be proven in our scheme.

Marek Sergot’s technical contributions range over different subjects. He has developed a series of novel ideas and formal methods bridging different research domains, such as artificial intelligence, computational logic, philosophical logic, legal theory, artificial intelligence and law, multi-agent systems and bioinformatics. By combining his background in logic and computing with his interest in the law, deontic logic, action, and related areas, and applying to all his capacity to understand the subtleties of social interactions and normative reasoning, Marek has been able to open new directions of research, and has been a reference, an inspiration, and a model for many researchers in the many fields in which he has worked.

We describe an approach that aims to unify certain aspects of access control and privacy. Our unified approach is based on the idea of axiomatizing access control in general terms. We show how multiple access control and privacy models and policies can be uniformly represented as particular logical theories in our axiom system. We show that our approach translates into different practical languages for implementation and we give some performance measures for some candidate implementations of our approach.

We describe an approach for distributed access control that is based on the idea of using a community-constructed repository of expressions of propositional attitudes. We call this repository an oracle. Members of a community may consult the oracle and use the expressions of belief and disbelief in propositions that are expressed by community members about requesters for access to resources. Our conceptual model and access control policies are described in terms of a computational logic and we describe an implementation of the approach that we advocate.

We describe an approach for distributed access control policies that is based on a nonmonotonic semantics and the use of logic programming for policy specification and the evaluation of access requests. Our approach allows assertions of relevance to access control to be made by individual agents or on a community-based level and different strengths of testimonial warrant may be distinguished by using various logical operators. We describe a form of ASP that allows for remote access request evaluation and we discuss a DLV-based implementation of our approach.

Our concern is to address the problem of sharing and exchanging policy information. For that, we propose a general conceptual framework for policies, a shared syntax and a shared semantics for a variety of policy types. The different policy types are all instances of the general policy framework that we describe.

In this paper we first introduce a logic for describing formally a family of delegation and revocation models that are based on the work in Hagström et al., We then extend our logic to accommodate an epistemic interpretation of trust within the framework that we define. What emerges from this work is a rich framework of formally well-defined delegation and revocation schemes that accommodates an important trust component.

We address the problem of providing data subjects with self-selected controls on access to their personal information. Existing approaches for this are not always sufficient in terms of offering the degrees of control and scope for individualization of access policies that are needed for personal data protection (and usage). We introduce a conceptual framework, a syntax, a semantics, and an axiomatization of a generalized form of access control meta-model, which may be specialized in various ways to enable data subjects to specify flexibly what access controls are to apply on their personal data.

We consider the problem of developing an abstract meta-model of access control in terms of which policies for protecting a principal's private information may be specified. Our concern is with developing the formal foundations of our conceptual model. For both the specific access control models and privacy policies, which may be defined in terms of the meta-model, we adopt a combining approach: we combine access control concepts to form the meta-model and we use a fibred logic for the formal foundations. Our approach enables data subjects to specify flexibly what access controls they wish to apply on their personal data and it provides a formal foundation for policies that are defined in terms of the meta-model.

We address the problem of defining access control policies that may be used in the evaluation of requests made by client actors, in the course of e-trading, to perform actions on the resources maintained by an e-collective. An e-collective is a group of agents that may act individually or in conjunction with other agents to satisfy a client's request to act. Our principal contribution to this key problem is to define formally an access control model in terms of which policies may be specified for helping to ensure that only legitimate forms of client actions are performed in the course of engaging in e-trading. We call this model the action control model. In action control, the notion of intentional, empowered, authorized actions, that may be performed individually or jointly with other agents and in a manner that is consistent with a group ethos, is the basis for specifying a set of permissives. A permissive is a generalization of the notion of permission (as the latter term is usually interpreted in access control). We define our action control model as a term rewrite system and we give examples of access policy representation.

The issue of representing access control requirements continues to demand significant attention. The focus of researchers has traditionally been on developing particular access control models and policy specification languages for particular applications. However, this approach has resulted in an unnecessary surfeit of models and languages. In contrast, we describe a general access control model and a logic-based specification language from which both existing and novel access control models may be derived as particular cases and from which several approaches can be developed for domain-specific applications. We will argue that our general framework has a number of specific attractions and an implication of our work is to encourage a methodological shift from a study of the particulars of access control to its generalities.

We address the problem of defining policies that may be used in the evaluation of requests made by client actors, in the course of web-based e-trading, to perform actions on the resources maintained by the server agents of an e-cooperative. An e-cooperative is a group of agents in cyberspace that may act individually or in conjunction with other agents to satisfy a client's request to act. Our principal contribution to this key problem is to define formally an event-oriented model in terms of which policies may be specified for helping to ensure that only legitimate forms of client actions are performed in the course of engaging in e-trading via the web. We call this model the Event-oriented Web-based E-trading (EWE) model. Policies defined in terms of the EWE model are used to specify a set of actions that client actors can perform as a consequence of the client having a particular status. We define the EWE model using a logic programming language and we give examples of web-based e-trading policy representation, validation and evaluation.

We address the problem of defining access control policies that may be used in the evaluation of requests made by client actors, in the course of e-trading, to perform actions on the resources maintained by an e-collective. An e-collective is a group of agents that may act individually or in conjunction with other agents to satisfy a client's request to act. Our principal contribution to this key problem is to define formally an access control model in terms of which policies may be specified for helping to ensure that only legitimate forms of client actions are performed in the course of engaging in e-trading. We call this model the action control model. In action control, the notion of intentional, empowered, authorized actions, that may be performed individualistically or jointly with other agents, and in a manner that is consistent with a group ethos, is the basis for specifying a set of permissives. A permissive is a generalization of the notion of a permission (as the latter term is usually interpreted in access control). In addition to the formal definition of the action control model, we give examples of action control policy specifications and we describe a candidate implementation and performance measures.

We describe the use of a flexible meta-interpreter for performing access control checks on deductive databases. The meta-program is implemented in Prolog and takes as input a database and an access policy specification. For processing access control requests we specialise the meta-program for a given access policy and database by using the logen partial evaluation system. The resulting specialised control checking program is dependent solely upon dynamic information that can only be known at the time of actual access request evaluation. In addition to describing our approach, we give a number of performance measures for our implementation of an access control checker. In particular, we show that by using our approach we get flexible access control with virtually no overhead, satisfying the Jones optimality criterion. The paper also shows how to satisfy the Jones optimality criterion more generally for interpreters written in the non-ground representation.

Standard SQL is insufficiently expressive for representing many access control policies that are needed in practice. Nevertheless, we show how rich forms of access control policies can be defined within SQL when small amounts of contextual information are available to query evaluators. Rather than the standard, relational structure perspective that has been adopted for fine-grained access control, we consider instead the representation of dynamic fine-grained access control (DFMAC) policy requirements at the access policy level. We also show how DFMAC policies may be represented in SQL and we give some performance results for an implementation of our approach.

Despite their widespread adoption, Role-based Access Control (RBAC) models exhibit certain shortcomings that make them less than ideal for deployment in, for example, distributed access control. In the distributed case, standard RBAC assumptions (e.g., of relatively static access policies, managed by human users, with complete information available about users and job functions) do not necessarily apply. Moreover, RBAC is restricted in the sense that it is based on one type of ascribed status, an assignment of a user to a role. In this article, we introduce the status-based access control (SBAC) model for distributed access control. The SBAC model (or family of models) is based on the notion of users having an action status as well as an ascribed status. A user's action status is established, in part, from a history of events that relate to the user; this history enables changing access policy requirements to be naturally accommodated. The approach can be implemented as an autonomous agent that reasons about the events, actions, and a history (of events and actions), which relates to a requester for access to resources, in order to decide whether the requester is permitted the access sought. We define a number of algebras for composing SBAC policies, algebras that exploit the language that we introduce for SBAC policy representation: identification-based logic programs. The SBAC model is richer than RBAC models and the policies that can be represented in our approach are more expressive than the policies admitted by a number of monotonic languages that have been hitherto described for representing distributed access control requirements. Our algebras generalize existing algebras that have been defined for access policy composition. We also describe an approach for the efficient implementation of SBAC policies.