Analysing Security Protocols Using Refinement in iUML-B

We propose a general approach based on abstraction and refinement for constructing and analysing security protocols using formal specification and verification. We use class diagrams to specify conceptual system entities and their relationships. We use state-machines to model the protocol execution involving the entities' interactions. Features of our approach include specifying security principles as invariants of some abstract model of the overall system. The specification is then refined to introduce implementable mechanisms for the protocol. A gluing invariant specifies why the protocol achieves the security principle. Security breaches arise as violations of the gluing invariant. We make use of both theorem proving and model checking techniques to analyse our formal model, in particular, to explore the source and consequence of the security attack. To demonstrate the use of our approach we explore the mechanism of a security attack in a network protocol.