## 4 Decentralization in IoT Security
### Applications of Blockchain in IoT  
In this section, we introduce various applications for which Blockchain has been deployed for IoT devices, as shown in Figure 6.  
_Internet of Vehicles (IoV):_ Many of the security and trust difficulties with Internet-connected vehicles could be resolved by implementing blockchain technology. Basic trust and security characteristics, such as vehicle identity management, reputation, communication channel integrity, system automation, etc., need to be guaranteed by a successful, dependable system [105; 106]. Social IoV (SIoV) is one such common example [107]. Smart contracts are adopted in this concept to implement tasks such as managing access, monitoring activities, etc. As an added bonus, privacy management via smart contracts is possible [108]. _Managing Supply Chain:_ Blockchain-empowered IoT devices can help improve the efficiency of the supply chain over the whole process, i.e., from the factory to the end user. IoT has shown strong potential to improve supply chain systems. However, there is an urgent demand to ensure the integrity and trustworthyness of data in such systems. According to to [109] and other sources, blockchain technology offers a definitive answer to this problem [110]. Particularly, smart contracts allow us to effectively build a fully automated supply chain management system without relying on any kind of centralized authority. Figure 6: Application of blockchain in IoT. Industrial Internet of Things (IIoT): Integrating smart edge devices into industries enables monitoring and maintenance of all processes with no need for human intervention [111]; this is where blockchain comes in. The integration of blockchain can further improve the reliability of the IIoT in terms of data trustworthiness, access control, privacy preservation, and security [112; 113]. Firmware Updates in IoT: The updating process of devices in IoT is also vulnerable to disruption, and the flow of code execution can be altered. There are also difficulties in distributing accurate firmware updates due to the restricted capabilities of IoT devices [6]. Another challenge is scalability; it is not feasible to manually update hundreds of endpoints. The majority of firmware update procedures rely on asymmetric cryptography technologies, which are notoriously difficult and resource-intensive. Regarding its decentralized structure, blockchain can effectively eliminate single points of failure [114; 115]. Smart Healthcare: A significant part of modern medical practice involves implanting sensors and other devices into patients for monitoring and diagnostic purposes. The IoT enables integrated sensors to gather data from patients to be shared with the doctor, who can then evaluate the patient's condition remotely. By taking this route, the patient can be freed from the hospital's hierarchical structure while still maintaining close contact with his or her physician. Strong interest exists in implementing such a cutting-edge IoT framework to guarantee real-time monitoring of patients, given the aging population and rising medical costs [11]. The Food and Drug Administration (FDA) and IBM Watson Health have collaborated on the use of blockchain technology to secure oncology-related data. They found that blockchain is able to store data collected from various sensors when all necessary conditions are met [116]. The healthcare industry is likely to adopt blockchain technology for safe storage of patient medical records. Blockchain can offer patients with unchangeable record confirmation and confidence in such a way that sensitive patient information can only be accessed by authorized personnel following designed protocols. Smart Grid: Recent increases in electricity production can be attributed to the utilization of cutting-edge IT methods that take into account consumer needs via the power grid.