I. Introduction
In an environment of growing power demand, the future smart grid is designed to run more efficiently, cost-effectively and reliably. This target is achieved by growing integration of information and communication technologies (ICTs). However, ICTs have also opened a door for potential attackers to intrude the system, and resulting cyber-attacks can have severe social, economic and physical consequences [1], [2]. For example, in December 2015, a power grid was compromised, triggering a major power outage and several hours of disruption to nearly 225, 000 citizens in Ukraine.