An operational framework to reason about policy behavior in trust management systems

In this paper we show that the logical framework proposed by Becker et al. to reason about security policy behavior in a trust management context can be captured by an operational framework that is based on the language proposed by Miller to deal with scoping and/or modules in logic programming in 1989. The framework of Becker et al. uses propositional Horn clauses to represent both policies and credentials, implications in clauses are interpreted in counterfactual logic, a Hilbert-style proof is defined and a system based on SAT is used to proof whether properties about credentials, permissions and policies are valid in trust management systems, i.e. formulas that are true for all possible policies. Our contribution is to show that instead of using a SAT system, this kind of validation can rely on the operational semantics (derivability relation) of Miller’s language, which is very close to derivability in logic programs, opening up the possibility to extend Becker et al.’s framework to the more practical first order case since Miller’s language is first order.Peer ReviewedPreprin

RelBAC: Relation Based Access Control

TheWeb 2.0, GRID applications and, more recently, semantic desktop applications are bringing the Web to a situation where more and more data and metadata are shared and made available to large user groups. In this context, metadata may be tags or complex graph structures such as file system or web directories, or (lightweight) ontologies. In turn, users can themselves be tagged by certain properties, and can be organized in complex directory structures, very much in the same way as data. Things are further complicated by the highly unpredictable and autonomous dynamics of data, users, permissions and access control rules. In this paper we propose a new access control model and a logic, called RelBAC (for Relation Based Access Control) which allows us to deal with this novel scenario. The key idea, which differentiates RelBAC from the state of the art, e.g., Role Based Access Control (RBAC), is that permissions are modeled as relations between users and data, while access control rules are their instantiations on specific sets of users and objects. As such, access control rules are assigned an arity which allows a fine tuning of which users can access which data, and can evolve independently, according to the desires of the policy manager(s). Furthermore, the formalization of the RelBAC model as an Entity-Relationship (ER) model allows for its direct translation into Description Logics (DL). In turn, this allows us to reason, possibly at run time, about access control policies

OWL-POLAR : A Framework for Semantic Policy Representation and Reasoning

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Shinren : Non-monotonic trust management for distributed systems

The open and dynamic nature of modern distributed systems and pervasive environments presents significant challenges to security management. One solution may be trust management which utilises the notion of trust in order to specify and interpret security policies and make decisions on security-related actions. Most trust management systems assume monotonicity where additional information can only result in the increasing of trust. The monotonic assumption oversimplifies the real world by not considering negative information, thus it cannot handle many real world scenarios. In this paper we present Shinren, a novel non-monotonic trust management system based on bilattice theory and the anyworld assumption. Shinren takes into account negative information and supports reasoning with incomplete information, uncertainty and inconsistency. Information from multiple sources such as credentials, recommendations, reputation and local knowledge can be used and combined in order to establish trust. Shinren also supports prioritisation which is important in decision making and resolving modality conflicts that are caused by non-monotonicity

The Audit Logic: Policy Compliance in Distributed Systems

We present a distributed framework where agents can share data along with usage policies. We use an expressive policy language including conditions, obligations and delegation. Our framework also supports the possibility to refine policies. Policies are not enforced a-priori. Instead policy compliance is checked using an a-posteriri auditing approach. Policy compliance is shown by a (logical) proof that the authority can systematically check for validity. Tools for automatically checking and generating proofs are also part of the framework.\u

Detection and resolution of normative conflicts in multi-agent systems : a literature survey

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Towards defining semantic foundations for purpose-based privacy policies

We define a semantic model for purpose, based on which purpose-based privacy policies can be meaningfully expressed and enforced in a business system. The model is based on the intuition that the purpose of an action is determined by its situation among other inter-related actions. Actions and their relationships can be modeled in the form of an action graph which is based on the business processes in a system. Accordingly, a modal logic and the corresponding model checking algorithm are developed for formal expression of purpose-based policies and verifying whether a particular system complies with them. It is also shown through various examples, how various typical purpose-based policies as well as some new policy types can be expressed and checked using our model

Audit-based Compliance Control (AC2) for EHR Systems

Traditionally, medical data is stored and processed using paper-based files. Recently, medical facilities have started to store, access and exchange medical data in digital form. The drivers for this change are mainly demands for cost reduction, and higher quality of health care. The main concerns when dealing with medical data are availability and confidentiality. Unavailability (even temporary) of medical data is expensive. Physicians may not be able to diagnose patients correctly, or they may have to repeat exams, adding to the overall costs of health care. In extreme cases availability of medical data can even be a matter of life or death. On the other hand, confidentiality of medical data is also important. Legislation requires medical facilities to observe the privacy of the patients, and states that patients have a final say on whether or not their medical data can be processed or not. Moreover, if physicians, or their EHR systems, are not trusted by the patients, for instance because of frequent privacy breaches, then patients may refuse to submit (correct) information, complicating the work of the physicians greatly. \ud \ud In traditional data protection systems, confidentiality and availability are conflicting requirements. The more data protection methods are applied to shield data from outsiders the more likely it becomes that authorized persons will not get access to the data in time. Consider for example, a password verification service that is temporarily not available, an access pass that someone forgot to bring, and so on. In this report we discuss a novel approach to data protection, Audit-based Compliance Control (AC2), and we argue that it is particularly suited for application in EHR systems. In AC2, a-priori access control is minimized to the mere authentication of users and objects, and their basic authorizations. More complex security procedures, such as checking user compliance to policies, are performed a-posteriori by using a formal and automated auditing mechanism. To support our claim we discuss legislation concerning the processing of health records, and we formalize a scenario involving medical personnel and a basic EHR system to show how AC2 can be used in practice. \ud \ud This report is based on previous work (Dekker & Etalle 2006) where we assessed the applicability of a-posteriori access control in a health care scenario. A more technically detailed article about AC2 recently appeared in the IJIS journal, where we focussed however on collaborative work environments (Cederquist, Corin, Dekker, Etalle, & Hartog, 2007). In this report we first provide background and related work before explaining the principal components of the AC2 framework. Moreover we model a detailed EHR case study to show its operation in practice. We conclude by discussing how this framework meets current trends in healthcare and by highlighting the main advantages and drawbacks of using an a-posteriori access control mechanism as opposed to more traditional access control mechanisms

Model Checking Social Network Models

A social network service is a platform to build social relations among people sharing similar interests and activities. The underlying structure of a social networks service is the social graph, where nodes represent users and the arcs represent the users' social links and other kind of connections. One important concern in social networks is privacy: what others are (not) allowed to know about us. The "logic of knowledge" (epistemic logic) is thus a good formalism to define, and reason about, privacy policies. In this paper we consider the problem of verifying knowledge properties over social network models (SNMs), that is social graphs enriched with knowledge bases containing the information that the users know. More concretely, our contributions are: i) We prove that the model checking problem for epistemic properties over SNMs is decidable; ii) We prove that a number of properties of knowledge that are sound w.r.t. Kripke models are also sound w.r.t. SNMs; iii) We give a satisfaction-preserving encoding of SNMs into canonical Kripke models, and we also characterise which Kripke models may be translated into SNMs; iv) We show that, for SNMs, the model checking problem is cheaper than the one based on standard Kripke models. Finally, we have developed a proof-of-concept implementation of the model-checking algorithm for SNMs.Comment: In Proceedings GandALF 2017, arXiv:1709.0176