Over the last 15 years, many policy languages have been developed for specifying policies and credentials under the trust management paradigm. What has been missing is a formal semantics - in particular, one that would capture the inherently dynamic nature of trust management, where access decisions are based on the local policy in conjunction with varying sets of dynamically submitted credentials. The goal of this paper is to rest trust management on a solid formal foundation. To this end, we present a model theory that is based on Kripke structures for counterfactual logic. The semantics enjoys compositionality and full abstraction with respect to a natural notion of observational equivalence between trust management policies. Furthermore, we present a corresponding Hilbert-style axiomatization that is expressive enough for reasoning about a system's observables on the object level. We describe an implementation of a mechanization of the proof theory, which can be used to prove non-trivial meta-theorems about trust management systems, as well as analyze probing attacks on such systems. Our benchmark results show that this logic-based approach performs significantly better than the only previously available, ad-hoc analysis method for probing attacks.

This article proposes a systematic study of information flow in credential-based declarative authorization policies. It argues that a treatment in terms of information flow is needed to adequately describe, analyze and mitigate a class of probing attacks which allow an adversary to infer any confid ential fact within a policy. Two information flow properties that have been studied in the context of state transition systems, non-interference and opacity, are reformulated in the current context of policy languages. A comparison between these properties reveals that opacity is the more useful, and more general of the two; indeed, it is shown that non-interference can be stated in terms of opacity. The article then presents an inference system for non-opacity or detectability, in Datalog-based policies. Finally, a pragmatic method is presented, based on a mild modification of the mechanics of delegation, for preventing a particularly dangerous kind of probing attack that abuses delegation of authority.

This paper proposes a systematic study of information flow in credential-based declarative authorization policies. It argues that a treatment in terms of information flow is needed to adequately describe, analyze and mitigate a class of probing attacks which allow an adversary to infer any confidential fact within a policy. Two information flow properties that have been studied in the context of state transition systems, non-interference and opacity, are reformulated in the current context of policy languages. A comparison between these properties reveals that opacity is the more useful, and more general of the two; indeed, it is shown that non-interference can be stated in terms of opacity. The paper then presents an inference system for non-opacity, or detectability, in Datalog-based policies. Finally, a pragmatic method is presented, based on a mild modification of the mechanics of delegation, for preventing a particularly dangerous kind of probing attack that abuses delegation of authority.

We present a declarative authorization language. Policies and credentials are expressed using predicates defined by logical clauses, in the style of constraint logic programming. Access requests are mapped to logical authorization queries, consisting of predicates and constraints combined by conjun ctions, disjunctions, and negations. Access is granted if the query succeeds against the current database of clauses. Predicates ascribe rights to particular principals, with flexible support for delegation and revocation. At the discretion of the delegator, delegated rights can be further delegated, either to a fixed depth, or arbitrarily deeply. Our language 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.

Administering and maintaining access control systems is a challenging task, especially in environments with complex and changing authorization requirements. A number of authorization logics have been proposed that aim at simplifying access control by factoring the authorization policy out of the hard-coded resource guard. However, many policies require the authorization state to be updated after a granted access request, for example, to reflect the fact that a user has activated or deactivated a role. Current authorization languages cannot express such state modifications; these still have to be hard-coded into the resource guard. We present a logic for specifying policies where access requests can have effects on the authorization state. The logic is semantically defined by a mapping to Transaction Logic. Using this approach, updates to the state are factored out of the resource guard, thus enhancing maintainability and facilitating more expressive policies that take the history of access requests into account. We also present a sound and complete proof system for reasoning about sequences of access requests. This gives rise to a goal-oriented algorithm for finding minimal sequences that lead to a specified target authorization state.

This paper presents a language, based on transaction logic, for specifying dynamic authorisation policies, i.e., rules governing actions that may depend on and update the authorisation state. The language is more expressive than previous dynamic authorisation languages, featuring conditional bulk insertions and retractions of authorisation facts, non-monotonic negation, and nested action definitions with transactional execution semantics. Two complementary policy analysis methods are also presented, one based on AI planning for verifying reachability properties in finite domains, and the second based on automated theorem proving, for checking policy invariants that hold for all sequences of actions and in arbitrary, including infinite, domains. The combination of both methods can analyse a wide range of security properties, including safety, availability and containment.

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.

MOTIVATION: A large amount of data on metabolic pathways is available in databases. The ability to visualise the complex data dynamically would be useful for building more powerful research tools to access the databases. Metabolic pathways are typically modelled as graphs in which nodes represent chemical compounds, and edges represent chemical reactions between compounds. Thus, the problem of visualising pathways can be formulated as a graph layout problem. Currently available visual interfaces to biochemical databases either use static images or cannot cope well with more complex, non-standard pathways. RESULTS: This paper presents a new algorithm for drawing pathways which uses a combination of circular, hierarchic and force-directed graph layout algorithms to compute positions of the graph elements representing main compounds and reactions. The algorithm is particularly designed for cyclic or partially cyclic pathways or for combinations of complex pathways. It has been tested on five sample pathways with promising results.