Unmanned Aerial Vehicle as Encryption Key Distributor for Secure Communications in Smart Grid

We use symmetric cryptography for secure communications with resource-limited smart grid control devices. We propose the novel idea of using the unmanned aerial vehicle (UAV) as a physical courier to carry secret key bits generated at the control center to remote control devices. While distributing secret keys, the UAV may be attacked in an attempt to sabotage secure communications. The UAV may fly a longer route to avoid attackers but it has a limited onboard battery capacity and must visit each device within a time limit to prevent a secret key deficit. We formulate an optimization to find the lowest attack risk flight route for secret key distribution while taking into consideration key deficiency and battery capacity. Such optimization is NP-hard. We further propose an efficient algorithm to find a low-risk flight route in less than a second, even for a large power grid system with more than a hundred nodes. For large systems, we modify the proposed algorithm to find a low-risk flight route as well as to determine the required UAV flight duration and battery size. Extensive simulation results confirm the superiority of the proposed algorithm against a baseline scheme that is ignorant of attackers.