*2.1. Unmanned Aerial Vehicles*

Unmanned aerial vehicles (UAVs), simply called drones, are specific robotic IoTs, which have electronic components, mechanical power modules, and onboard operating systems to execute complicated tasks. According to their flying mechanisms, UAVs can be categorized as multi-rotor-wing drones, fixed-wing drones, and hybrid fixed/rotary-wing drones [24]. Regarding the range and altitude that a done can be remotely operated at, UAV platforms can be classified into two types: low-altitude platforms (LAPs) and high-altitude platforms (HAPs). Original UAVs were mainly used for battlefields, with advancements in hardware, software, and networking infrastructure, but there has been increasing usage of UAVs in civilian and commercial applications.

Owing to their unmanned nature and requirements for remote wireless communication, modern UAV-aided systems are vulnerable to different attacks [25]. Thus, the continued use of UAVs increases the need for cyber-awareness including UAVs in the airspace, the development of the automatic dependent surveillance broadcast (ADS-B), and the risk of cyber intrusion. The Federal Aviation Administration (FAA) mandates the national adoption of ADS-B, which uses "plaintext" to broadcast messages in avionics networks. Such an unencrypted ADS-B manner introduces serious privacy and security vulnerabilities, such as message spoofing for false aircraft position reports. As a result, current radar-based air traffic service (ATS) providers seek to preserve privacy and corporate operations of flight plans, position, and state data. Moreover, the privacy of aircraft track histories is mandatory and only accessible to authorized entities within UAM networks. In addition, it is necessary to ensure confidentiality, availability, and integrity for urban aircraft data accessing and sharing data during UAM operations.
