A Blockchain-Based Security Scheme for Vehicular Ad Hoc Networks in Smart Cities Xue Jun Li Department of EEE Auckland University of Technology Auckland, New Zealand xuejun.li@aut.ac.nz Maode Ma College of Engineering Qatar University Qatar mamaode@qu.edu.qa Yong Xing Yong School of EEE Nanyang Technological University Singapore e160206@e.ntu.edu.sg Abstract— The development of Vehicular Ad Hoc Networks (VANET) has brought many advantages to facilitate the deployment of the Intelligent Transportation System (ITS). However, without proper protection, VANETs can be vulnerable to severe cyber-attacks. This paper explores the threats to the VANETs and proposes a security scheme for VANETs with a Blockchain (VNB). Furthermore, the proposed VNB with Ethereum was developed. With a graphical user interface, experiments were conducted. For ad hoc communications, a vehicle can randomly select another vehicle, and VNB will authenticate the selected vehicle with the Blockchain and Trusted Authority (TA). Preliminary test results successfully proved that Blockchain can be the key technology to mitigate the security threats to VANETs. Keywords—vehicular ad hoc networks, blockchain, security I. INTRODUCTION Vehicular ad hoc networks (VANETs) play an important role in the Intelligent Transportation System (ITS). In 1999, the US Federal Communication Commission (FCC) allocated 75 MHz in the spectrum of 5.850-5.925 GHz for Dedicated Short Range Communications (DSRC) for VANETs. The communication protocol works based on Wireless Access for Vehicular Environments (WAVE) also known as IEEE 802.11p [1-3]. As ITS involves high-speed moving vehicles and requires a simple mechanism for communication, VANETs allow an arbitrary vehicle to communicate with nearby vehicles and infrastructure to disseminate real-time traffic messages. Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communications are enabled in a VANET. To achieve that, an On-Board Unit (OBU) is equipped in every vehicle and Road Side Unit (RSUs) are deployed along a road [2]. In addition, a Trusted Authority (TA) and application servers are installed. The TA is responsible for identity management and registration [4]. V2V communication enables broadcast information like vehicle speed, turning direction, etc. With the aid of a RSU, a vehicle gets safety and traffic information from the TA through V2I communication. A VANET is designed mainly to focus on crash prevention, safety and traffic control, which is considered as one of the most prominent technologies to provide efficiency and safety for ITS [5]. Experts predicted that it can prevent up to 80% of the accidents involving non-impaired drivers. However, a VANET can be vulnerable to the following adversaries items [4]: (1) selfish drivers, who may deliberately inject false traffic information in the system to maximize their benefits; (2) eavesdroppers, who spy on other drivers to deduce their behaviour or travelling pattern for future information attacks; and (3) malicious attackers, who may use sophisticated tools to disrupt the communication in a VANET for the certain financial gain. Apart from the abovementioned adversarial behaviours, a VANET is also vulnerable to the following types of cyber attacks: (1) Denial of Service (DoS) attack, which will make the VANET unavailable to vehicles. This can be done by jamming the channel with dummy messages, which prevents a legitimate user from sending critical safety messages. Eventually, it may lead to a system crash. (b) Privacy Violation: To prevent impersonation, the identity of the sender of a message is shown, which would reveal the driver’s identity, location, actions and preference. This violates their privacy. (c) Message Alternation: This attack is done where messages are altered. For example, when a driver decides to send a hazard message, it can be changed from hazard to non-hazard message, which may lead to devastating consequences. To address those security issues, a secure VANET requires the following features: (1) authentication to verify the identity of a user; (2) message integrity to prevent any form of tampering; (3) message non-repudiation to track down the cause of an accident; (4) entity authentication to ensure the sender of a message is active in the network; (5) access control to prevent unauthorised information access; (6) message/user information confidentiality to protect privacy; (8) availability to ensure system resilience; (9) real- time guarantee to provide collision avoidance and valid information. These requirements motivate us to study the possibility of applying Blockchain in VANETs. The rest of this paper is organised as follows. Section II briefly reviews Blockchain and existing works on the security schemes for VANETs. Section III presents the proposed security scheme in VANETs with a Blockchain, followed by its implementation in computer simulations in Section IV. Section V presents its simulation results with discussions and Section VI concludes the paper. II. RELATED WORK A. Blockchain A blockchain [6] is a decentralized, shared, distributed and append-only ledger, which is used to facilitate the process of recording transactions and tracking assets. Its name originated from the fact that it stores transaction data in blocks that are linked together to form a chain. Due to its versatility, a blockchain can be used in many industries such as financial services, insurance, government, supply chain management, healthcare, and the Internet of Things (IoT). The most popular application of blockchain is the Bitcoin.