Security of Transportation Networks: Modeling Attacker-Defender Interaction

Transportation networks are increasingly facing new security threats due to the vulnerabilities of cyber-physical components that support their operation. In this article, we aim to understand how the network operator (defender) should prioritize the investment in securing a set of facilities in order to limit the impact of a strategic adversary (attacker) who can target a facility to increase the overall network cost. We adopt a game-theoretic approach to model the defender-attacker interaction and study two models: normal-form game – where both players move simultaneously; and sequential game – where attacker moves after observing the defender’s strategy. For each model, we provide a complete characterization of how the set of facilities that are secured by the defender in equilibrium vary with the cost of attack and per-facility defense cost. We also identify the set of vulnerable facilities; i.e., the facilities in the support set of attacker’s equilibrium strategy. Importantly, our analysis provides sharp conditions relating the cost of attack and defense cost for which the defender has the first mover advantage. In particular, by securing all vulnerable facilities at an appropriate level of effort in a proactive manner, the defender is able to fully deter the attacker from targeting any facility.