## 3 Related Work on Protection against Sybil Attacks
The solution makes it possible to detect a Sybil attack separately for each car. In order to provide tamper-free periodic digital signatures to neighboring vehicle nodes, it requires the approved infrastructure. [PERSON] [46] suggested a strategy based on a distributed partnership between the roadside units that would allow for a local database providing instant information on vehicles on the road. This knowledge includes the positions in which they associate and  
Figure 3: Sybil attack in VANET. the real positions determined based on trilateration between three RSUs using the obtained signal intensity (RSS). In another early analysis, [PERSON] et al. [47] proposed a lightweight protection regime focused on estimating the node's location by analyzing its distribution of signal power. Three functions are delegated to vehicles in this strategy. The claimer is a vehicle that emits beacon signals periodically, including its name and location. The witness is a vehicle within the signal spectrum of the applicant. Witness nodes calculate the claimant's signal strength and then store this information in their memory along with the claimant's respective personal data. Thus, they hold a neighbor list that will be transmitted in the next beacon post [48]. When a beacon alert is sent, the vehicles are waiting for a period of time to obtain the previous calculations from the applicant's witness nodes. Then, they will determine the approximate location of the claimant. RSUs are used to certify the cars' location behind them to be confident of the car's path. [PERSON] et al. [49] suggested a privacy-preserving detection system without requiring cars to reveal their information on the infrastructure. The Department of Motor Vehicles (DMV) assigns a separate set of pseudonyms instead of assigning precisely one ID to each car, and pseudonyms in the same pool are hashed to a standard value. As a result, a car can use any alias in its pool and maintain its privacy. Related in forms of privacy security, [PERSON] et al. [50] have developed a protocol that helps vehicles detect a Sybil attack in a collaborative manner. The protocol uses party signatures to preserve anonymity and mobility trace similarities. It involves three phases: probing, verifying, and quarantine of nodes. [PERSON] et al. [34] created the solution depending on the similarity of motion trajectories of Sybil nodes, which are impractical and inappropriate in the real world, believing that Sybil nodes always have the same position and motion trajectories. The solution makes it possible to detect a Sybil attack separately for each car. In order to provide tamper-free periodic digital signatures to neighboring vehicle nodes, it requires approved infrastructure. Finally, one of the potential solutions for identifying the Sybil node may be the resource test. The machine sends complex mathematical problems randomly to the nodes that are supposed to be answered within a given time. Attackers that simulate several nodes are not willing and able to overcome all sent formulas, compromising their simulated cars [19]. The comparison of mentioned methods is presented in Table 2.