Formal modelling and analysis of XML firewall for service-oriented systems

Firewalls have been designed as a major component to protect a network or a server from being attacked. However, due to their emphasis on packet filtering rather than verifying user permissions and examining packet contents, conventional firewalls are not suitable for protecting service-oriented systems from unauthorised service invocations. In this paper, we present a formal XML firewall security model for service-oriented systems, which supports user authentication and role-based user authorisation according to policy rules that can be updated dynamically. The formal model consists of two major components, namely the application model and the XML firewall model, which are designed compositionally using coloured Petri nets. We analyse both the application model and the XML firewall model using an existing Petri net tool, and demonstrate how key properties of the formal models can be verified, and how design errors can be detected and corrected at an early design stage.