## 4 Modified Blockchain Model
### The Proposed Algorithm
#### 4.6.3 Preliminaries and Notations
As mentioned earlier, applying blockchain technology has a negative impact on the space, as a copy of the data is attached to every node. It also costs a large number of messages exchanges to perform blockchain tasks such as proposing, voting, and consensus. In addition, the cost of computation increases as a result of decentralization, in which every validator runs validation processes and processes for consensus calculations [1]. On the other hand, the use of blockchain technology results in many advantages that enhance its performance. In fact, having direct communication among nodes and devices speeds up communication. In addition, having smart contracts within a blockchain enables the automation of processes and actions. In fact, smart contracts and consensus decisions both give more reliability to blockchain technology. Another vital advantage of blockchain technology is scalability, where large numbers of IoT sensors, wearable devices, users' devices, and others can be adapted. Blockchains also facilitate the management, coordination, and cooperation of heterogeneous components within systems. One of the main advantages is the ability to manage the components and identities of users, processes, services and ownerships. Those elements interweave many processes and are subject to change over time, which is a challenging task. Moreover, the procedures of validation in blockchains clearly challenge attempts at manipulation. Such features reduce the chances of aborting transactions and blocks, which improves the performance, since these abortions waste execution time. Indeed, all aborted transactions should be rolled back and re-executed again. Some studies have shown that the abortion of read transactions costs about 80% of the total execution time [43]. ### Sensors and Wearable Devices

The development of sensors and wearable devices has enhanced their uses in many fields of technology. There are various categories of wearable devices, i.e., clothes like smart shirts, accessories such as watches and earbuds, and embedded wearable devices such as biosensors and smart tattoos. The use of wearable devices has many advantages, such as providing real-time data and responses. It supports data accessibility, availability, automation, and control. On the other hand, wearable devices cause some weaknesses to the systems from the point of view of security, energy, and computation abilities. Actually,most wearable devices use Bluetooth technology for communication, which is considered a vulnerable communication technology from a security perspective. Therefore, it should be supported with advanced security protocols and techniques for key generation, key characteristics, key exchange, and data encryption, as well as to detect malicious and infected devices. However, having advanced security protocols and techniques is challenged by computation and energy capabilities that are limited as a result of the sizes of wearable devices [15]. In this case, the system should balance the computation and energy capabilities on one side, and security on another side. It also should balance the computation and energy capabilities with the quality of data. Actually, to overcome the challenge of computation, it is recommended to exploit the computation power of other system components or faraway servers [45; 46]. It could also outsource the computation and processing tasks in case the data are not sensitive. Moreover, for energy consumption, there are different kinds of energy technology that can be involved in enhancing wearable devices, such as renewable energy that comes from nature (e.g., sun, wind, and body temperature). ### Risk Management

At the end this discussion, it is important to highlight risk management for the modified blockchain model. Firstly, blockchain technology promises to change centralized management by enforcing democratic decision-making techniques through data sharing and voting.