Evil Twins: Handling Repetitions in Attack–Defense Trees: A Survival Guide

Abstract : Attack–defense trees are a simple but potent and efficient way to represent and evaluate security scenarios involving a malicious attacker and a defender – their adversary. The nodes of attack–defense trees are labeled with goals of the two actors, and actions that they need to execute to achieve these goals. The objective of this paper is to provide formal guidelines on how to deal with attack–defense trees where several nodes have the same label. After discussing typical issues related to such trees, we define the notion of well-formed attack–defense trees and adapt existing semantics to correctly capture the presence of repeated labels.