# Blockchain Application in Internet of Vehicles: Challenges, Contributions and Current Limitations
## 2 Background: Blockchain for the IoV  
Blockchain technology is one of the most current topics that has piqued the interest of many companies and researchers owing to the numerous advantages it offers over conventional alternatives, such as cryptography techniques and trust management. Blockchain is a distributed database that does not require a central authority and does not require third-party verification. A blockchain is composed of blocks, and each block has a hash of the preceding block, forming a chain of blocks from the genesis block to the present block (i.e., genesis block does not relate to a prior block). Most nodes should register their agreement in order to record a transaction in the distributed ledger. This necessitates the use of a consensus mechanism. Proof of Stake (PoS) and Proof of Work (PoW) are the most frequent and widely used consensus algorithms. Blockchain has the potential to provide significant benefits in a variety of industries and applications, including IoV. This new technology shares some common features that involve decentralization, transparency, immutability, better security, anonymity, cost reduction and autonomy.  
It is evident within the literature that blockchain is widely used for addressing the privacy and security concerns of a variety of use cases. However, it is of paramount importance to highlight that blockchain is complementing existing techniques such as cryptography (e.g., elliptic curve cryptography) and identity management (e.g., self-sovereign identity management and the K-Anonymity algorithm).  
As briefly stated in the Introduction, the Internet of Vehicles is regarded as being among the most active research domains in ITS, integrating VANET and IoT. The IoV combines two scientific visions: (a) vehicle connectivity and (b) vehicle intelligence, focusing on the integration of objects such as persons, cars, things, networks and surroundings [24]. Because of the combination of communication and information technology in the IoV, it is advantageous in addressing numerous traffic and driving difficulties, which contributes to the safety of passengers and the overall driving experience [25]. Therefore, based on the existence of multiple technologies in the IoV ecosystem, researchers proposed an architecture consisting mostly of four layers [26; 27].  
1. The first layer (i.e., the sensing layer) comprises all the sensors within the vehicles, which collect data and identify particular events of interest such as driving patterns, vehicle circumstances, weather conditions, etc.
2. The second piece (i.e., the communication layer) enables various wireless communication modes (e.g., V2V and V2I). The communication layer ensures that existing and future networks are always connected (such as GSM, Wi-Fi, LTE and Bluetooth, among others).
3. The third layer (i.e., computing) is in charge of storing, analyzing, processing and making decisions regarding various circumstances in the IoV network. This layer also provides data computing services.
4. Finally, the application layer is the highest level of the IoV and may provide consumers with a range of vehicle services.  
Figure 1 displays an example of a hybrid blockchain and IoV architecture in light of the preceding discussion. The blockchain acts as a governance layer and may be viewed as a bridge between the communication and application layers [24; 27; 28; 29]. In such an expanded IoV architecture, blockchain may supply blockchain-based solutions and bundle data into new blocks. Furthermore, it may leverage incentive mechanisms to incentivize users to share information resources by rewarding a certain number of tokens, allowing users to actively contribute transaction information to the system.