# Towards the Detection of GPS Spoofing Attacks against Drones by Analyzing Camera's Video Stream
## 2 Related Work  
In this section, we review prior studies that proposed countermeasures against GPS spoofing. The GPS protocol is vulnerable to spoofing attacks, since it lacks encryption and authentication mechanisms. As a result, attackers can inject false GPS signals using software-defined radio (SDR) [7] or dedicated GPS spoofers (which can be purchased online), causing the drone to believe that it is flying in a location that differs from the actual location. Studies have shown that GPS spoofing attacks against drones can cause a drone flying in autonomous mode to accelerate in the attacker's chosen direction [8] (by transmitting fake GPS coordinates in the opposite direction); force a drone flying in manual mode to land [9] (by sending a no-flight zone alert that triggers a safety mechanism, causing the drone to land); or change the direction of the drone's movement itself [10]. Other studies have suggested countermeasures against GPS spoofing attacks by integrating additional hardware. One study [3] suggested the use of a multi-receiver for GPS spoofing detection to detect malicious fake signals, by verifying the GPS measurements using the fixed distances between the receivers and then measuring the distances between the receivers' reported locations. When the GPS signal is legitimate, the distance will be similar to the fixed distances, but when there is a GPS spoofing attack, the measured distances will be very close to zero, as all the receivers are spoofed with the same fake location; this method would be difficult to implement with small drones, because additional hardware is needed for all of the GPS receivers. SPREE [4], a method presented in another study, is a countermeasure for GPS spoofing attacks that can also detect takeover attacks; it relies on the auxiliary peak method, which is used in combination with a navigation message inspector in which the strongest satellite signal as well as other weaker environment signals are tracked. SPREE's main disadvantage is that external hardware is needed. Another study [11] suggested the use of Iridium signals to detect Global Navigation Satellite System (GNSS) spoofing. The authors reverse engineered parameters from the Iridium satellite constellation, such as the satellite's speed, packet interarrival times, maximum satellite coverage, satellite pass duration, and satellite beam constellation. With those parameters, they proposed a solution for the detection of a target user's deviations from his/her path caused by a GNSS spoofing attack. The main disadvantage of the proposed method is the requirement to provide the parameter values for each user, which may be a barrier to a consumer without this capability. Another study proposed SemperFi [12], a single antenna GPS receiver capable of tracking legitimate GPS satellite signals and estimating the drone's true location (even during a spoofing attack); this method relies on a comparison of satellite signals' time of arrival (ToA) in order to determine whether a GPS spoofing attack occurred. This solution's main disadvantage is that the consumer is dependent on the manufacturer, which is responsible for the solution's implementation, and cannot implement the solution him/herself. In a paper presenting a similar solution that deals with the GPS signal [13], the authors proposed a receiver that uses maximum plausibility estimates after the validator signal is dropped, in order to assess the correct location. Other studies suggested countermeasures that do not rely on GPS for navigation and instead rely on the cellular network; for example in [14], the authors presented \"drive me not\", a GPS spoofing detection method that utilizes mobile cellular network infrastructure to validate the position received by the GPS infrastructure. Other research [15] utilized UpLink's received signal strength (RSS) measurements for cross-position validation for GPS spoofing detection. In another study [16], the authors built a network of clustered ground base stations (BSs) that cooperatively serve a number of UAV-UEs.