# Secure Trust-Based Blockchain Architecture to Prevent Attacks in VANET
## 3 Motivation  
This section discusses the challenges faced in the VANET environment and the implications they bring to the genuine nodes in the network during the occurrence of network attacks. The major challenge faced in the VANET environment is the mobility of the nodes, which can be an RSU, vehicles that are stuck in the traffic congestion, or one vehicle moving at a fast pace. The nodes within the system itself have challenges in communicating [6]. The mutual communication window during a high-velocity scenario is kept small, only a few seconds, due to the small transmission range. Besides, the communication system has to cope with the Doppler effect, frequent link failures, wastage of network bandwidth, and high end-to-end delay for high relative velocity [30]. Although nodes have a high period of message exchange, they must deal with the problems related to high vehicular traffic density, such as frequent data collision, channel fading, message dropping due to expired waiting time, and other interference problems. Due to the coverage area of vehicles, the connectivity can be lost with the high mobility and might travel in the opposite direction which makes the nodes' connectivity extremely ephemeral. Long live context is lacking in VANET systems, where a hotspot with a long-life password from the user node is required and is at the same time impractical for securing volatile connections. Privacy in keeping their personal details private, protected, and not exposed by the drivers will be quite difficult when the system is set to give identities to all the individual vehicles in order to avoid Sybil attacks. Each vehicular node has the right to keep its personal details from other nodes while not violating the privacy, no matter of the situation. For example, during an accident, the legal investigation is allowed to access data without any denial, and it is an advantage for the liability that provides the opportunity for open investigation platform. Since there is no global authority that handles the standards for VANET systems, and the scale of the network increases every single day--approximately more than 750 million nodes--the problem of standardization arises. For instance, the standards for the same car brand are different in different countries or continents, and also totally distinguishable for different brands of car. A node in the context of the VANET system can be placed in a high-density network, such as a traffic jam, or in a low-density network, such as a highway roadway with no or fewer surrounding vehicles. In a low-density network, an advanced information message dissemination using a store-and-forward message is transmitted instead of the immediate message forwarding [31]. The same message has the possibility of repeating multiple times by the same vehicle due to this case scenario. In the case of a high-density network, this is achieved by choosing only selected vehicles given permission to send a repeated message. The density of the node is influenced by the road and time, which is commonly measured as high during the daytime compared to other times [32]. In the case of high density, the opposite must be achieved, with only selected vehicles allowed to send repeated messages. The vehicular node follows a predefined path instead of a random path, as different roads come with various characteristics [33]. Compared to rural and highway roads, urban roads are usually a dense roadway with numerous vehicles, buildings, and other obstacles. As the characteristics of the roadways differ, the movement pattern of the vehicular nodes varies too due to the challenge they pose for an efficient communication [6]. For example, urban roads are not as highly ordered as the highway roads in terms of movement. Heterogeneity is also a challenge in the VANET system, as every single node has its own characteristics depending upon its applications, be it either a stationary node, such as RSU, or a mobile node, such as the vehicles.