## 4 Modified Blockchain Model
### The Proposed Algorithm
#### 4.6.3 Preliminaries and Notations
It also shows the total number of messages for the traditional blockchain that includes 240 blocks of type _Block_. Obviously, the total number of messages using modified blockchain is reduced by about 53% compared to the traditional blockchain model. Figure 6: The detailed execution time for the validation process of read and write transactions within Block1, Block2, and Block using a traditional blockchain and a modified blockchain. ## 6 Discussion

This section discusses blockchain technology in general, as well as the proposed modified blockchain that is illustrated in this work. It also discusses the IoT and wearable device specifications which may enhance our model. ### Decentralization

One of the main characteristics of using blockchain technology is decentralization, where the blockchain eliminates the central authority, since every node and device in the blockchain network can generate data and all decisions are made according to the consensus. This allows for fault tolerance, as it does not have a single point of failure. This means the system keeps running even if there are some faulty or failed components. In addition, every node in the blockchain has an up-to-date copy of the data, which helps to avoid centralized data storage. Actually, this supports data availability, accessibility, and recovery if needed [20]. However, it costs more space, time, computation, communication, and energy to manage the data's consistency. ### Security

Another important feature of blockchain technology is security, which also includes authentication, authorization, and privacy. The structure of a blockchain allows us to

Figure 8: The number of messages using traditional blockchain and modified blockchain. Figure 7: (**a**) Shows the Relationship between Number of Messages and Number of Nodes where the Number of Blocks is Constant, Highlighting the Number of Messages for Block1, Block2 and Block; (**b**) Shows the Relationship between Number of Messages and Number of Blocks where the Number of Nodes is Constant. have multiple copies of data ledgers, which facilitates discovery and recovery in case of data misusing or corruption issues. Every block in the ledger is secured through a hash number that considers the content of the current block and the hash of the previous block in the ledger. This prevents any change in the ledger or the blocks as the chain of the hash numbers is changed, which can be directly discovered, and the approval of such a change is reached through consensus, which makes it impossible. Moreover, a blockchain allows direct communication between any two nodes, which helps to authenticate every communication. The authentication is performed using smart contracts and encryption. Smart contracts include some conditions, and if those conditions are satisfied, specific actions are taken. It is an automatic code that is immutable (cannot be changed) and distributed (so every node knows the actions it takes) [26]. In our model, every node and device in the blockchain has a unique ID, authority, privilege, and role, which are listed in a smart contract. Upon any communication, the nodes or devices authenticate each other through smart contract. This also helps to validate whether the communication or the requested action is authorized. This is implemented using a private or public key, which allows for validated authorization of access or updates to any data. This guarantees privacy and control. Furthermore, the transferred data and patient identities are encrypted for privacy purposes. In fact, according to the healthcare specifications, there are different levels of data sensitivity, and there are specific considerations for some patients, such as some governmental or military officials. Thus, different levels of security protocols, encryption techniques, and privacy procedures can be applied. ### Performance

It is important to discuss the performance in cases of applying blockchains in healthcare systems.