## 1 Introduction  
The Vehicular Ad hoc Networks (VANETs) has been instrumental in advancing intelligent transportation systems, notably through Vehicle-to-Infrastructure (V2I) and Vehicle-to-Vehicle (V2V) communications, as shown in Figure 1. However, disconnected areas, often remote or rural, face a significant challenge due to the scarcity of Roadside Units (RSUs). This scarcity hampers robust vehicular communication, making direct V2V interactions for message authentication crucial [1]. Such conditions highlight the need for reliable communication methods to ensure trust between vehicles. Our research introduces the Pre-Signature scheme, tailored to enhance secure V2V communication in areas with limited RSUs support. This scheme is central to building trust between vehicles, ensuring safety and operational integrity in disconnected environments. It hinges on the exchange of Reputation Values among vehicles, establishing a decentralized trust mechanism in the absence of RSUs. Additionally, the scheme incorporates Pseudonym Certificates (PCs) and the Security Credential Management System (SCMS) for secure offline communication. In SCMS, the Certification Revocation List (CRL) plays a key role in identifying and blocking misbehaving vehicles from the network. However, the synchronization of the CRL becomes imperative when vehicles gain access to the infrastructure, notably through _RSUs_[2; 3]. A Pre-Signature scheme offers a more scalable and granular approach than CRLs by leveraging a reputation system. This system assesses vehicles based on their historical behavior, providing a more nuanced view of reliability and trustworthiness. Our focus is on effectively disseminating the Reputation Value (RV) for offline use while maintaining privacy. The goal is to develop a system to authenticate messages, which maintains privacy, works offline, and allows reputation to be used. Referring to Figure 2, reputation+offline can be delivered by foregoing pseudonyms and providing medium-term (e.g., daily) Reputation Value certificates. Reputation+privacy can be delivered by requesting a short-term RV certificate every time a new Pseudonym Certificate is used. Finally, privacy + offline is delivered by systems like SCMS. The challenge is to deliver all three of these properties in a scalable way, with minimal changes to the standards. Our innovative solution involves a new cryptographic primitive--the Pre-Signature. This two-step process allows vehicles to verify Reputation Values offline, without compromising sender privacy. A significant contribution of this study is the employment of Simulation of Urban Mobility (SUMO) simulation on an aerial communication map of the Peak District, a National Park in central England. It is worth noting that our work is based on the SCMS framework that relies on Dedicated Short-Range Communication (DSRC) rather than using the internet, e.g., via sattelite or GSM. The distinct advantages here are high-bandwidth and low-latency capabilities, even in challenging weather conditions, high-speed scenarios, or remote locations. The proposed scheme is based on real-world considerations regarding coverage. For example, in rural areas with limited connectivity or in disaster-hit regions where infrastructure is damaged, traditional methods of online verification are not feasible. Figure 1: VANET Communications Infrastructure. Through a detailed 24 h simulation, we analyze vehicle communication in rural areas under different conditions with limited RSUs connectivity. This simulation is pivotal in demonstrating the practical effectiveness and feasibility of the Pre-Signature scheme, showing its capacity to bolster trust and reliability in challenging and disconnected regions. The results play a pivotal role in demonstrating the scheme's ability to improve communication trust and reliability, providing significant insights into its practical application in real-world rural environments.