Modelling and Analysing Access Control Policies in XACML 3.0

XACML (eXtensible Access Control Markup Language) is a prominent access control language that is widely adopted both in industry and academia. XACML is an international standard in the field of information security. The problem with XACML is that its specification is described in natural language (c.f.

GM03,Mos05,Ris13) and manual analysis of the overall effect and consequences of a large XACML policy set is a very daunting and time-consuming task. In this thesis we address the problem of understanding the semantics of access control policy language XACML, in particular XACML version 3.0. The main focus of this thesis is modelling and analysing access control policies in XACML 3.0.

There are two main contributions in this thesis. First, we study and formalise XACML 3.0, in particular the Policy Decision Point (PDP). The concrete syntax of XACML is based on the XML format, while its standard semantics is described normatively using natural language. The use of English text in standardisation leads to the risk of misinterpretation and ambiguity.

In order to avoid this drawback, we define an abstract syntax of XACML 3.0 and a formal XACML semantics. Second, we propose a logic-based XACML analysis framework using Answer Set Programming (ASP). With ASP we model an XACML PDP that loads XACML policies and evaluates XACML requests against these policies.

The expressivity of ASP and the existence of efficient implementations of the answer set semantics provide the means for declarative specification and verification of properties of XACML policies. Overall, we focus into two different area. The first part focuses on the access control language. More specifically our focus is on the understanding XACML 3.0.

The second part focuses on how we use Logic Programming (LP) to model access control policies. We show that there is a relation between XACML and LP through their semantics. We close the thesis by presenting applications in analysing access control properties and a case study. These applications show that these two approaches (AC paradigm and LP paradigm) can be combined together.

We close the thesis by presenting applications in analysing access control properties and a case study. We present access control security policies in a Smart Grid from Smart Meter perspective.