  This article addresses the problem of automatically generating attack trees
that soundly and clearly describe the ways the system can be attacked.
Soundness means that the attacks displayed by the attack tree are indeed
attacks in the system; clarity means that the tree is efficient in
communicating the attack scenario. To pursue clarity, we introduce an
attack-tree generation algorithm that minimises the tree size and the
information length of its labels without sacrificing correctness. We achieve
this by i) introducing a system model that allows to reason about attacks and
goals in an efficient manner, and ii) by establishing a connection between the
problem of factorising algebraic expressions and the problem of minimising the
tree size. To the best of our knowledge, we introduce the first attack-tree
generation framework that optimises the labelling and shape of the generated
trees, while guaranteeing their soundness with respect to a system
specification.
