# Securing Smart Grid Enabled Home Area Networks with Retro-Reflective Visible Light Communication
## 1 Introduction  
Smart grids are modern electricity distribution systems that monitor, protect, and automatically optimize the operation of interconnected elements including generation equipment, high-voltage distribution, automation systems, and energy storage [1]. As a subset of smart grids, smart microgrids operate in a grid-connected mode and offer the benefits of distributed computing and communications to deliver real-time information and enable the instantaneous balancing of electrical supply and demand at the level required for each discrete device [2]. The ability of smart microgrids to deliver electricity to loads in a home area network (HAN) on a targeted, as needed basis is important to their success. Internal access to HAN energy management systems enables microgrid operations to perform multi-tier custom diagnostics and make selective decisions to schedule load shedding and level demand in real time. Electricity loads (consuming devices) can be divided into groups based on the degree of need for electricity. They are commonly categorized as sensitive, adjustable, or sheddable [2]. Tier 1 loads (sensitive) are those that must operate continuously without fail, such as elevators, refrigeration equipment, and emergency lighting. Tier 2 loads are discretionary (adjustable) and may be shifted or shed for short periods to balance generation availability. Examples include domestic water heating systems, certain fans, and air conditioning loads. Tier 3 loads (sheddable) are those that can be shed for emergency operations due to unplanned and partial loss of generation. Some loads may fall into different tier classifications based on the seasonor time of day. Inside a smart home, a HAN connects different tier loads including smart appliances, IoT sensors, and other electric devices to the energy management system of a smart grid through a HAN gateway (or smart meter). Smart appliances and devices will adjust their run schedule to reduce electricity demand on the grid at critical times and lower consumers' energy bills [3]. The charging of a plug-in electric vehicle can also be managed over a HAN, e.g., bidirectional charging and electric vehicles for mobile storage [4]. The HAN can balance the demand of electricity across the household and prioritize between electric vehicles and other appliances to manage electricity usage and reduce costs. By adding more plug-in electric vehicles to the grid, we have the potential to reduce fuel costs, lower our dependency on foreign oil, and help reduce greenhouse gas emissions [3]. Short range radio-based wireless communication technologies, such as Zigbee, Bluetooth and WiFi, are existing candidates in a HAN that support two-way communication between the smart appliances, IoT sensors, electric vehicles, and the gateway [5]. However, this comes with a price as omnidirectional radio signals are vulnerable to intentional interceptions. Common cyber attacks in a wireless HAN include passive attack, masquerading, replay attack, denial of service (DOS) attack, and man-in-the-middle (MITM) attack [6]. Some of the attacks impose threats on individual household user privacy, while other attacks may even cause a widespread blackout by gaining control of portions of the grid. Although each wireless candidate has its unique security concerns (e.g., Zigbee shares the key with appliances, Bluetooth places the device into discoverable mode, and WiFi garners considerable interest from the hacker community), one common feature of these radio-based technologies causing the vulnerabilities is their wide interception range. Without sophisticated methods to protect the encryption keys, the data communication through the wireless channels are completely exposed to the public. In a WiFi-based HAN, pre-shared key WPA and WPA2 remain vulnerable to password cracking attacks [7]. Once adversaries discover the pre-shared key (PSK), they can potentially decrypt all packets encrypted with the PSK.