Formal Engineering of XACML Access Control Policies in VDM++

We present a formal, tool-supported approach to the design and maintenance of access control policies expressed in the eXtensible Access Control Markup Language (XACML). Our aim is to help developers evaluate the consequences of policy decisions in complex situations where security requirements change and access decisions may depend on the external dynamic environment. The approach applies the model-oriented specification language from the Vienna Development Method (VDM++). An executable formal model of XACML access control is presented in VDM++. The use of the model to analyse and revise both policies and requirements on the environment is illustrated through an example. An approach to the practical problem of analysing access control in virtual organisations with dynamic membership and goals is proposed.