# Blockchain-Based Authentication in Internet of Vehicles: A Survey
## 1 Introduction  
With the huge increase in the number of vehicles on roads nowadays, more accidents and traffic congestion issues are encountered. This raises the need for serious arrangements to ensure roads' safety and traffic efficiency. Different technologies have been introduced towards maintaining safer and time-efficient driving on roads, such as, Vehicular Ad-hoc Networks (VANETs) in which the vehicles exchange data about their speed, location, etc., and other road-related information to raise their awareness about surrounding road conditions and help them making better and effective decisions. However, with the rapid advancement in today's technologies such as ubiquitous connectivity, wireless technologies, sensor devices, smart vehicles, and cloud computing platforms, the need for more powerful vehicular networks has increased. Hence, the IoV has appeared that can exploit and incorporate all these advanced technologies in order to provide more satisfying real-time services for vehicles' drivers and passengers. IoV has emerged with great potential to support various services and offer several benefits to the transportation system such as cost effectiveness, time efficiency, road safety [1], traffic management [2, 3, 4], evolution of smart cities [5, 6], autonomous driving [7, 8, 9, 10] alarms and dynamic warning systems [11, 12, 13] as well as recording fatal occurrences [14]. However, in order for the IoV system to be able to secure such services, enormous amounts of dataneed to be generated and exchanged among the different IoV entities including vehicles, pedestrians, and roadside infrastructure. Since this information exchange takes place through an open-channel wireless network, the exchanged messages are vulnerable to various security attacks that could undermine the privacy of the communicating entities and the confidentiality of their data via eavesdropping or even affect the integrity of the transmitted messages by tampering them before reaching their target destination. Other types of security attacks that could be encountered in IoV environments are the attacks that target the authenticity of users. Here, a malicious entity masquerades a legitimate user and may commit malicious activities in the network. Therefore, efficient authentication is necessary to prevent such attacks in IoV. On the other hand, blockchain technology has recently drawn the attention of both industry and academia due to its efficient characteristics represented in decentralization, immutability, consensus, fault tolerance, and enhanced security. Blockchain was first known as the enabling technology behind Bitcoin or cryptocurrency. Yet, it has recently attracted various emerging domains such as smart cities [15; 16; 17], smart grids [18; 19; 20], Internet of Things (IoT) [21; 22], Cyber Physical Systems (CPS) [23; 24; 25], robotics [26; 27], machine learning [28; 29], and health systems [30; 31; 32]. IoV platforms have also started to adopt blockchain for various services which include data management [33; 34], resource trading [35; 36], resource sharing [37; 38], vehicle management [39; 40], ride sharing [41; 42], traffic control [43; 44], and forensics applications [45; 46]. In this paper, we highlight the use of blockchain in IoV and VANETs for authentication by surveying a number of recent blockchain-based authentication schemes. Numerous surveys have recently been published discussing the authentication approaches and protocols in the vehicular networks of VANETs and IoV which are summarized in Table 1. Some of the surveys have focused on authentication in IoV and/or VANETs as part of the Intelligent Transportation Systems (ITS) whereas others have exhibited wider perspective by discussing IoV authentication as a subsection of the Internet of Things (IoT) technology.