# Cross-Domain Access Control Model in Industrial IoT Environment
## 6 Conclusions  
In this study, we designed a master-slave chain structure and proposed a highly scalable and trusted cross-domain access control authentication model to solve the access control problem of resources among devices in different domains. For the master chain security problem, a reputation-based dynamic selection strategy of master-chain nodes is used. In the reputation-based master chain node selection mechanism, by evaluating the historical consensus behavior of the nodes, the consensus nodes with more honest consensus have a higher reputation, and the nodes with malicious consensus behavior are punished so that it is difficult for them to recover with a higher reputation value. Periodically, the edge node with the highest reputation in each domain is selected as the master chain node. In addition, for the special environment of the IIoT domain, the paper proposes an access control method based on the combination of roles and attributes to achieve high fine-grained access control. Finally, to address the attribute strategy matching rate problem, a grouping strategy-based matching algorithm is proposed to improve the efficiency of attribute strategy matching by constructing policy groups into policy trees so that a large number of irrelevant strategies can be excluded in the matching process. The experimental results show that the master-slave chain structure improved the throughput by 82% over the single-chain structure. There was also an improvement in the throughput and latency compared to the results of other studies.  
For future work, expanding the scale of experiments and optimizing the consensus algorithm of the blockchain should be considered to create a service environment with higher performance, lower latency, and higher bandwidth for the blockchain network than the existing scheme. In addition, to further improve intelligent access control, machine learning techniques can be combined to improve access control and optimize the cross-domain access control model. Finally, in real-life blockchain-based access control systems, there are diverse and heterogeneous IoT environments, which will bring many challenges to the network latency, system operation, and unified management of the access control system, which is already our future optimization target.  
Conceptualization, X.W. and Z.Z.; methodology, Z.Z.; software, S.W.; validation, X.W., Z.Z. and S.W.; formal analysis, Z.Z.; investigation, Z.Z.; resources, X.W.; data curation, S.W.; writing--original draft preparation, Z.Z.; writing--review and editing, Z.Z.; visualization, S.W.; supervision, X.W.; project administration, X.W.; funding acquisition, X.W. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Natural Science Foundation of China (62062006, 62062008, 62067001, 61762008), the Natural Science Basis Research Plan in Guangxi Province of China (2018J/A170028, 2019J/A170045, 2018J/A170194), the Special Funds of the Guangxi Bagui Scholars and the National Key Research and Development Program of China (2018 YFB1404404). (Corresponding author: [PERSON]).  
Not applicable.  
The authors declare no conflict of interest.