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Top1. Introduction
Current growths in wireless communication technologies and automobile industries have generated significant attention in Vehicular Ad-hoc networks (VANET) over the last few years. In VANETs each vehicle is furnished by smart devices like GPS, Wi-Fi, On-board Unit (OBU) and sensors, etc. (Martinez et al., 2010), which allows it to act as a wireless vehicle and can perform vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication (Li et al., 2007). It implements an intelligent transportation system (ITS), notifying drivers to avoid awful traffic situations through disseminating beacons, event messages, and infotainment messages. These messages are key steps towards improving overall traffic conditions, driving assistance, and vehicle safety.
However, the unique characteristics of VANET, i.e., openness, high mobility, and dynamic topology, enable the malicious vehicle to perform misbehaving activities on the messages, i.e., message modification, message drop, broadcasting bogus message, and so on (Li et al., 2007), (Hamdi et al., 2014), Hasrouny et al., 2017). These malicious activities are severe and cannot be solved by existing security solutions (Kumar and Maheshwari, 2014), (Pradweap et al., 2013), (Han et al., 2014), resulting in the degraded service of VANET.
Security is one of the main issues in VANETs and requires reliable message delivery through the authenticated vehicle as all the applications are based on the exchange of messages. The establishment of trust is the best solution to ensure the reliability of the messages and their sender. Trust can be defined as a subjective belief of a vehicle about another vehicle belonging to the same geographical zone. It helps each vehicle to detect the dishonest or malicious vehicle fabricating messages or its identity.
According to the evaluation object (entity or data or both), existing trust models are divided into three categories: vehicle-centric, message-centric, and combined trust model. Vehicle-centric detects malicious vehicles by evaluating each vehicle behavior, message-centric ensure reliable data delivery by measuring the trustworthiness of the messages and combined trust model to evaluate the trustworthiness of both vehicles and messages.
In existing trust models, each vehicle trustworthiness is evaluated by considering only event messages. The integrity and trustworthiness of each communicated message critically impact the quality of the applications in VANET. Beacon messages play an important role in position related VANET applications. They construct traffic views, access location-based services, and evaluate warning messages (A. Rachedi et al., 2015). Therefore, false beacons may mislead the vehicle to make the right decisions in packet forwarding or accessing location-based services. These false beacon messages result in choosing a misbehaving vehicle as the next forwarder. Infotainment messages are forwarded to access the non-safety services, e.g., a real-time parking navigation system is used to inform drivers of any available parking space, internet access, toll payment, etc. These messages play the least role in securing the VANET. But essential to offer convenience and comfort to drivers and passengers. Event messages avoid catastrophic situations and improve traffic efficiency by informing drivers timely and correctly. But a modified or delayed event message may incur severe costs on a network, even loss of human life.