Ninth International Conference on Deontic Logic in Computer Science (DEON'08)

The idea of norms presupposes agency, and agency presupposes an indeterministic causal order (so that "ought" does not imply "is"). So much can be modeled in "branching time with agents and choices" (BTAC). The seriously ontological independence of agentive choices, however, requires, as a necessary condition, a causal order permitting space-like separation of those choices in a sense definable in "branching space-times with agents and choices" (BSTAC). Let us idealize an agent, when restricted to a single space-time, as a kind of spatio-temporal "worm" in the familiar way, representing the life of the agent in that space-time. Then a representation of "the agent," since it must include representation of seriously objective choices, must look like a tree with two kinds of branching. In both kinds of branching, there is a single past-pointing worm-like representation of the past-life of the agent up to the branching, and an entire assemblage of distinct worm-like representations of the possible future-life of the agent subsequent to the branching, one for each history in which the life of the agent continues. The first kind of branching occurs at choice-points for the agent. According to BSTAC, such branching will involve a last point of agent's-choice-not-yet-made (say, a last point of deliberation), but no first point of agent's-choice-has-been-made in any possible future-life of the agent. In the second kind of branching, the agent is passive, having two or more possible future-lives due to space-like-related choices by other agents, or by metaphorical "choices" by some space-like-related element of Nature. In this case, BSTAC says that there will be no last point of the past-life of the agent, but instead a first point for each of the agent's possible future-lives.

The economics of information security has recently become a thriving and fast-moving discipline. As distributed systems are assembled from machines belonging to principals with divergent interests, incentives are becoming as important to dependability as technical design. The new field provides valuable insights not just into security topics such as privacy, bugs, spam, and phishing, but into more general areas such as system dependability (the design of peer-to-peer systems and the optimal balance of effort by programmers and testers), and policy (particularly digital rights management). This research program has been starting to spill over into more general security questions (such as law-enforcement strategy), and into the interface between security and the social sciences. Most recently it has started to interact with psychology, both through the psychology-and-economics tradition and in response to phishing. The promise of this research program is a novel framework for analyzing information security problems {one that is both principled and effective.

While access control appears in various guises in many aspects of computer systems, it is attractive to reduce it, as much as possible, to few central concepts and rules. The development and use of general logics for access control is an ongoing effort in this direction. In this talk, we examine several logics for access control and discuss some of their intended applications. Some of the principles that we consider come from modal logic, computational lambda calculus, and other standard formal systems. Others stem from ideas in security, such as delegations of authority and the Principle of Least Privilege.

This is an intuitive description of our approach to modelling contrary to duty obligations. We shall describe our ideas through the analysis of typical problematic examples taken from Carmo and Jones [6], L. van der Torre [14] and Prakken and Sergot [5].