## 3 Literature Review
### Blockchain-Based IDMSs
Blockchain technology was used to provide authentication and identification processes to users and service providers across a variety of health domains. A smart contract was implemented in the proposed system using Ethereum. In edge computing, the privacy and security of user data are two of the most important factors that need to be considered. As discussed in [22], the authors used smart contracts as a means of presenting the Access Management System by using blockchain technology. In order to improve the Internet of Things IIoT privacy, the authors in [15] proposed verifiable anonymous identity management systems (VAIM), through which they improved blockchain identity management and enhanced the unlinkability of the system by using zero-knowledge proof (ZKP) algorithms. User privacy has been affected by third-party dependencies in identity management systems in a variety of fields, including the Internet of Things. An SPOF is also one of the most important issues resulting from third-party control. Using Hyperledger Fabric, the authors in [13] implemented a smart-home-based scenario architecture to improve the quality and efficiency of home sensors and to enhance IoT centralization issues. A proposed architecture would divide the functions of the system into three main parts: registration, authorization, and revocation. The authors tried to improve the scalability of the system by splitting the functions. The authors in [32] attempted to solve the problem of electronic health records information being exposed, which poses a threat to the privacy of the users and those whose records are accessed. The authors implemented a proof of concept through the use of Hyperledger Fabric's permissioned blockchain technology to ensure anonymity for the EHR data and to enhance privacy for patients. Using a DNS-like approach, the authors of [23] proposed a DNS-IDMs architecture that is implemented on Ethereum's permissioned ledger. In order to enhance the privacy of the user, users and service providers would be able to create identity attribute claims and verify them using the services of real-world identity attribute benefactors. By using blockchain transactions, users can also control and manage their identities. There are many security challenges associated with large-scale IoT systems due to centralization concepts, such as unauthorized access requests to IoT-enabled devices, which are an issue of access control. To make the system more flexible and adaptable, reference [14] implemented a private blockchain POC prototype using Ethereum and smart contracts. BlendCAC was the name of the framework proposed by the authors. An Ethereum-based IDM cloud protocol was proposed by [27], an improved version of CIDM (Consolidated Identity Management). The proposed protocol attempts to solve the third-party reliance problem in traditional identity management systems. Smart contracts were used in the proposed system to increase data transmission privacy and to enhance system flexibility. The authors of [24] provided a method that allows users to sign transactions using a different Ethereum identity in order to enhance user untraceability by granting the user the right to delete their data and allow them to discard their identity afterward. The proposed method represents identity through web3 js-based implementation and data erasing can be requested by the user or an end of service. It was proposed in [25] that attribute trust could be enhanced by using an Attribute Trust-enhancing Identity Broker (ATIB) architecture in order to enhance the aggregation of system attributes by following the ten SSI principles. As part of the proposed proof of concept, the service providers role would be enhanced with the help of the protocol manager, which is the main component in the proposed architecture that will be able to support the implementation of many identities and access protocols to the system.