Measuring the security posture of IEC 61850 substations with redundancy against zero day attacks

As one of the most critical components of the smart grid, substations are responsible for distributing the energy to end users. According to the substation automation standard, IEC 61850-90-4, substations contain highly complex and interconnected networks, which are typically designed with redundancy to improve the availability in case of failures. The redundancy usually takes the form of multiple subsystems with identical functionality, such that one failed subsystem would not affect the normal operation of the entire substation. However, we show that such redundant subsystems are not always effective against malicious attacks, because, unlike natural faults, attackers may deliberately target the weakest link, i.e., common vulnerabilities found in multiple subsystems. In this paper, we first present a detailed substation configuration designed based on IEC 61850 and industrial practices. We then devise a novel security metric, namely, the factor of security, to measure the effectiveness of redundant subsystems against unknown zero day attacks. We apply the metric to two concrete attacks scenarios, time delay attack, and the tripping circuit breakers attack. Finally, we evaluate the metric through simulations.