Computing Exact Outcomes of Multi-parameter Attack Trees

In this paper we introduce a set of computation rules to determine the attacker's exact expected outcome based on a multi-parameter attack tree. We compare these rules to a previously proposed computational semantics by Buldas et al . and prove that our new semantics always provides at least the same outcome. A serious drawback of our proposed computations is the exponential complexity. Hence, implementation becomes an important issue. We propose several possible optimisations and evaluate the result experimentally. Finally, we also prove the consistency of our computations in the framework of Mauw and Oostdijk and discuss the need to extend the framework.