# Detecting and Mitigating Attacks on GPS Devices
## 4 Factors Contributing to GPS-Denied or GPS-Disrupted Environments
### GPS Spoofing  
Commercial GPS signals are not authenticated or protected from malicious attacks, including GPS spoofing, where an attacker broadcasts falsified GPS signals, allowing a receiver to believe they are in a different position. This type of attack is easy to generate due to the low signal strength of the downlink GPS signal, making it easier for the malicious attacker's signal to overwhelm the actual GPS signal at the receiver. This attack type is more relevant to the L1 carrier since it does not have any type of protection and is less relevant to the L2 carrier since the L2 carrier implements cryptographically protected codes. Consequently, this type of attack is more relevant to commercial and consumer GPS receivers. There are a limited number of papers that discuss real-world examples of GPS spoofing attacks; however, the authors of [56] did provide a discussion of some real-world examples, such as the well-known \"Iran-US RQ-170 incident\", where Iranian forces captured a Lockheed Martin RQ-170 Sentinel UAS using a GPS spoofer in December 2011, which was publicly confirmed by the US military shortly after the event took place. The authors of [56] also discussed the work conducted by researchers from the University of Texas at Austin in 2013 and 2014. The authors built a GPS spoofer using low- and no-cost hardware and software components and then successfully spoofed a UAS and a ship. The spoofer caused the ship to travel in a zigzag motion while the ship's autopilot reported a straight line of travel. The authors of [57] described the results of experiments conducted to seize control of a UAS navigation system through GPS spoofing. They systematically analyzed how to transmit falsified GPS signals and then prevent detection to maintain UAS control. The authors of [58] presented research where they implemented a GPS spoofer and injected the spoofed signal into a GPS receiver embedded within a UAS testbed. That GPS receiver was not providing stand-alone navigation but was rather part of a fusion approach that combined GPS data with inertial sensors. The authors demonstrated that even in this multi-sensor fusion approach, GPS spoofing was effective and that the UAS testbed's navigation system was compromised. The study presented in [58] did not utilize an actual UAS but rather a testbed running the actual flight control software of a commercial UAS. So while the results must be caveated as such, these results still clearly illustrate the effectiveness of GPS spoofing. GPS spoofers can be coherent, meaning they are phase and frequency synchronized with the actual GPS signal, or non-coherent, meaning they are not phase and frequency synchronized with the actual GPS signal. The authors of [59] presented a theoretical relationship between GPS spoofing signal synchronization error and required GPS spoofing signal power. The authors of [59] then provided practical advice and guidance on optimizing system design to GPS spoofing system designers. The authors of [60] also provided an analysis of potential GPS spoofer system design choices, focusing on potential techniques and strategies a spoofing system may employ in an attempt to minimize detection. Coherent GPS spoofing is more difficult to implement but can have a greater impact on the target receiver and requires stronger detection mechanisms within the receiver. The authors of [61] developed an advanced digital signal processor (DSP)-based GPS spoofer that was capable of high-fidelity civil GPS signal creation with significant carrier phase and Doppler frequency offset accuracy, such that the spoofed signal was virtually indistinguishable from authentic GPS signals. This work aimed to study the effectiveness of potential defense mechanisms against spoofing attacks. Many potential defenses were postulated;however, the authors concluded that cryptographic authentication was required against a sophisticated spoofing attack. Many studies have established that low-cost GPS spoofers can be implemented using commercial SDR hardware and open-source software.