## 4 Blockchain Technology for Security  
According to the procedure, the blockchain contract record is turned into a sensor information record. Each datum block in the blockchain system comprises two components: a header and then a body, which are generated every 10 min. Many pieces of information are in the header block, including the current block number, previous block hash value, current timestamp, random-value (nonce), current block hash value, and Merkle tree. Most of the sensor data are included in the units or blocks content. Every sensor data point is continuously stored in the data block of the research system, where the operator can access it. Each element of the sensor data acquired is digitally signed by the Merkle tree in the block, ensuring that there are no repetitions of the sensor information. Once the system has received all the sensor data, \"Merkle-root values\" are created using the Merkle-tree hash algorithm in the block's header [58]. Blockchain architecture is shown in the following figure. A vital component of the blockchain system is the untranslatability of the timestamp and sensor data. In the contemporary digital age, the timestamp serves as a digitalized postmark and is an essential security component. The timestamp is used to offer exact \"proof of time\" and certification of every record modification or transaction content since it serves as the time stamp for every electronic file or transaction. The electronic timestamp indicates a message or document's creation date and time by assigning a specific time. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Paper** & **Security** & **Efficiency** & **Reliability** & **Decentralized** & **Drawbacks** \\ \hline
[7] & Moderate & Moderate & Yes & No & Integrity is possible in this system \\ \hline
[14] & Low & Moderate & No & Non-centralized & The verification process is low \\ \hline
[17] & Moderate & Moderate & No & Yes & More chances of security attacks \\ \hline
[25] & Moderate & Low & No & Yes & An unknown person can attack transmission \\ \hline
[28] & Low & Low & No & Yes & Weakness of private information \\ \hline
[29] & High & Moderate & yes & Yes & Cannot bear the fault \\ \hline
[30] & Low & Moderate & No & Yes & The complication in data transactions \\ \hline
[32] & Moderate & Low & No & Yes & Low hashing power \\ \hline
[35] & High & Moderate & No & No & No assurance of privacy of data \\ \hline
[38] & Low & Moderate & No & Non-centralized & The verification process is low \\ \hline
[41] & Low & Low & No &
\begin{tabular}{c} Client-server \\ architecture \\ \end{tabular} & Not secure, any node data can be dropped during transmission. \\ \hline
[42] & Moderate & Moderate & yes & Peer to Peer & Not secure for private data \\ \hline
[48] & High & Moderate & No & No & Privacy assault can be initialized, but it is unreliable for large transactions. \\ \hline
[51] & High & Low & No & Yes & lack of reliability and systematic evaluation \\ \hline
[57] & Moderate & High & Yes & Yes & Need confidentiality \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison table of previous studies. Even if a certificate is terminated or cancelled after a timestamp is created, it still has the nonrepudiation feature. The timestamp and sensor data cannot be changed, which is an essential feature of the blockchain system. In today's world, the timestamp serves as a digitalized postmark and is an essential security element. The timestamp is used to validate any record modification or transaction content since the moment of stamping for any electronic file or transaction, which provides precise \"proof of time.\" In order to establish when communication or a document was made, the electronic timestamp lends a precise time to it. The nonrepudiation functionality remains active even if a certificate is revoked or canceled after a timestamp is generated. The central node idea is still there in the dispersed network design, and many central node conceptions may exist. Each primary node is connected to other auxiliary nodes.