## 2 State-of-the-Art: A Review
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Years** & **Authors** & **Focus** \\ \hline
2018 & [PERSON] et al. [12] & Authors have proposed a monitoring system based on smart contract to identify malicious usage of electrical power. \\
2018 & [PERSON] et al. [22] & Authors have introduced the energy BC based on the consortium BCT and the Stackelberg game. \\
2018 & [PERSON] et al. [26] & Authors have implemented a token-based private decentralized energy trading system. \\
2018 & [PERSON] et al. [27] & A four-layer framework based on smart contract BCT for fine-grained access control system is proposed for Industry 4.0. \\
2019 & [PERSON] et al. [13] & Authors have proposed a four-layer architecture for the concept of Blockchain of Things (BCoT) in industrial applications. \\
2019 & [PERSON] et al. [14] & Authors have proposed a new architecture based on smart contract for client and resource registrations in IIoT. \\
2019 & [PERSON] et al. [25] & Authors have proposed a data protection framework based on distributed BC. \\
2019 & [PERSON] et al. [28] & Authors have proposed a hybrid technique based on BC and ML to detect attacks for energy-trading applications. \\
2020 & [PERSON] et al. [29] & Authors have proposed a reinforcement learning technique to address the block time minimization and transaction throughput of blockchain-based IIoT networks. \\
2021 & [PERSON] et al. [15] & Authors have proposed a new architecture based on smart contract, BC and ML for quality control in smart manufacturing application. \\
2021 & [PERSON] et al. [30] & Authors have proposed BCT applications for Industry 4.0 such as manufacturing data protection, automotive, information and security. \\
2021 & [PERSON] et al. [31] & An IIoT framework based on BC for sensor authentication is proposed by the authors. \\
2021 & [PERSON] et al. [32] & The paper exposes the main enabling technologies for Industry 4.0 such as IoT, Artificial Intelligence, cloud computing and BC. \\
2021 & [PERSON] et al. [33] & Authors present the various metrics for the usage of BC in manufacturing. \\
2021 & [PERSON] et al. [34] & Authors propose BC and IoT-based product traceability system for textile manufacturing applications. \\
2022 & [PERSON] et al. [35] & The review paper discusses the BC applications in Industry 4.0 such as authentication, asset tracking and smart contract exchange. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Related works based on Blockchain/ML for Industrial IoT. [PERSON] et al. [22] introduced the energy BC for secure energy trading in Industrial IoT based on the consortium BCT and the Stackelberg game. [PERSON] et al. [26] implemented a token-based private decentralized energy trading system in decentralized smart grid energy, which can be applied to the IoE. Therefore, the IoE provides an innovative concept to increase the visibility of energy consumption in the Smart Grid. The authors in [27] propose a framework named BSeIn that is a BCT-based system for secure mutual authentication to enforce fine-grained access control polices. Furthermore, BSeIn ensures confidentiality, privacy and multifactor authentication. [PERSON] et al. [13] proposed a new architecture based on four layers for industrial applications. In addition, the authors define the concept of merging BC and IoT in one system named Blockchain of Things (BCoT). Likewise, a new architecture based on three layers for supplier chain applications among supplier, producer, factor and customer is suggested by [PERSON] et al. [14]. The latter architecture is based on a distributed ledger BC to ensure traceable transactions among untrusted peers. In modern power systems, [PERSON] et al. [25] proposed a data protection framework based on distributed Blockchain, which can resist against data manipulation that is triggered by cyber attackers (e.g., false data injection attacks). To guarantee data accuracy, [PERSON] et al.