Network Topology-aware Mitigation of Undetectable PMU Time Synchronization Attacks

Time Synchronization attacks constitute a major threat to PMU-based smart grid applications, their cost-efficient detection and mitigation is thus of utmost importance. In this paper we propose a mitigation approach based on authenticated network-based time synchronization. Our approach relies on the observation that a time synchronization attack can be undetectable if and only if it targets at least three time references in the power system, and such attacks need to be mitigated through appropriate security controls. We first provide a formal proof of this result, including a characterization of the degrees of freedom of the attacker in constructing an attack. We then formulate the problem of mitigating undetectable attacks at minimum cost as an integer linear program, and prove that it is NP-hard. To solve the problem, we propose two approximation algorithms based on (1) computing shortest paths, and (2) solving a linear relaxation of the problem. Extensive simulations suggest the superiority of the proposed algorithms on IEEE benchmark power system graphs compared to baseline solutions. We report mitigation cost savings of at least 76% compared to a naive approach for mitigation and at least 30% compared the state-of-the-art. Authors