# Distributed Reputation for Accurate Vehicle Misbehavior Reporting (DRAMBR)
## 1 Introduction  
In recent years, the advancement of Intelligent Transport Systems (ITS) has led to significant research in the field of Vehicular Ad hoc Networks (VANETs). The U.S. Department of Transportation (U.S. DOT) highlights the need to ensure that connectedvehicles operate in secure, safe, and privacy-protective networks [1]. A security system is required as vehicles exchange critical information with other vehicles, wireless mobile devices, traffic management centers, and roadway infrastructure. VANETs, as shown in Figure 1, play a vital role in enabling seamless real-time information exchange between vehicles to improve safety, optimize traffic flow, and enhance the efficiency of the overall driving experience. However, the reliability of information sharing between vehicles becomes increasingly challenged in disconnected areas characterized by sparse infrastructure and where connectivity is intermittent. In these scenarios, the probability of malicious actions occurring without detection is increased, which leads to hazardous and undesirable situations. Thus, detecting and reporting misbehavior in such conditions is crucial and requires an accurate scheme that works offline without relying on an infrastructure. Vehicles need a reliable way to autonomously assess the trustworthiness of information based on factors like reputation scores. A further difficulty is differentiating between genuine system errors, such as those resulting from imperfect GPS data, and intentional misbehavior, a task that necessitates highly precise validation processes. Given the real-time requirements of vehicular networks, balancing data accuracy and computational efficiency poses a dilemma. In addition, the emphasis on privacy protection using certificates to maintain anonymity complicates the process of misbehavior detection. Figure 1: VANET communications infrastructure. Source: [2]. Existing standards for misbehaving detection and reporting rely on the Mishehavior Authority (MA) in the Security Credential Management System (SCMS) [3]. In this system, if enough misbehavior is reported for a certain vehicle, the vehicle certificates will be revoked and added to the Certification Revocation List (CRL). This will be updated and distributed to other vehicles in the environment. Once other vehicles identify that a message came from a vehicle on the CRL, it will no longer be considered a trusted node for sending and receiving messages [4]. However, in the implementation of SCMS in disconnected vehicular networks, two primary challenges arise, as depicted in Figure 2.  
1. Firstly, maintaining and synchronizing the CRL is crucial for identifying the misbehaving vehicles. The CRL must be constantly updated and shared with all vehicles, a process that requires regular access to network infrastructure, typically via Roadside Units (RSUs). This becomes problematic in areas with limited connectivity as the CRL grows with the number of misbehaving vehicles, necessitating frequent online updates. 2. CRL size and retrospective unlinkability: The SCMS is responsible for revoking misbehaving or malfunctioning vehicles' Pseudonym Certificates (PCs). However, putting all valid vehicle certificates on the CRL would make it very large. The system needs an efficient scheme to perform the revocation without revealing the PCs used by the vehicle before it started misbehaving. As a result, vehicles could be using expired or invalid certificates that might call into question the security, trustworthiness, and accuracy of the misbehavior reports they transmit. To address these challenges, we need a system that ensures vehicles detect and report misbehavior accurately and maintain privacy while establishing trustworthiness, even without constant internet connectivity. Reputation systems have been proposed as a means to strike a balance between anonymity, security, and trust, especially in offline settings. In this paper, we propose a Distributed Reputation mechanism for Accurate vehicle Misbehavior Reporting (DRAMBR).