## 4 Identity Management and Access Control Based on Blockchain under Edge Computing for IIoT
### System Setup and Operation  
This section describes the establishment and operation of the hierarchical network architecture. The process can be divided into the following distinct phases: Network establishing, registering edge centers and manufacturing terminals into the system, defining access control policies for edge centers and manufacturing terminals, and changes in access control policies of nodes. The operation process is shown in Figure 4.  
Figure 4: Setup and operation of access control with identity management.  
(1) Network establishment: Each industrial control edge networks and blockchain network is constructed. The blockchain network is created by edge centers, which manages industrial control edge networks. Each manufacturing terminal and edge center has a unique identity. Once the blockchain network is established, edge centers will build access management and identity management mechanisms for manufacturing terminals in the blockchain network.  
Each industrial control edge network and manufacturing terminal can be connected to an adjacent edge center, which is also a node in the blockchain network. The edge center is responsible for building and managing data access policies and identity management information, which are stored in the blockchain.  
(2) Registration and authentication: The blockchain nodes need to know the address of the smart contract before registering as a miner. After the information is obtained, it can send the transaction to the feature registration manager. Thereafter, once the transaction is successfully accepted into the blockchain, the cloud computing center will receive its registered address [41].  
(3) Identity management: Edge centers can register manufacturing terminals under the control of the cloud computing center. Manufacturing terminals can be registered on any nearby edge center based on their own conditions. The identity management policy of each terminal is stored in the blockchain. The terminals should be able to verify the identity before the access operation.  
(4) Access policy definition: Manufacturing terminals define access control rules for their stored resources. There are several ways to define their permissions. The article uses an attribute-based access control mechanism to define a list of attributes for access rights and lists network devices that have access to specific resources.  
(5) Access policy modification: The access control rights of the resources can be changed. The manufacturing terminal negotiates with the edge center to modify its access control policy. If the edge center modifies the access policy of a terminal, it will be verified and modified in the blockchain network.  
(6) Modification of management rights: As mentioned earlier, manufacturing terminals must be managed by edge centers. When an edge center needs to transfer management control to another node, add, or remove other edge centers from the system, it needs to be implemented through blockchain transactions.  
One advantage of our approach is that transferring administrative control of IIoT devices is a simple process, because all operations in the system are defined and implemented using blockchain transactions, and the edge centers do not need to interact with everyone.