# An Empirical Study of a Trustworthy Cloud Common Data Model Using Decentralized Identifiers
## 2 Related Works
### Decentralized Identifier (DID)
An agent is any application that stores and uses DIDs. It is the software that interacts with other entities via DIDs. The verifiable DID model consists of three roles, issuer, holder, and/or verifier. Figure 1 presents a basic DID model proposed by the World Wide Web Consortium (W3C). The statements of verifiable credentials are generated by an issuer. The presentations based on the credential are sent to the verifier to attest the authenticity of verifiable credentials issued by the issuer. Hyperledger Indy is a public and permissioned blockchain platform tailored to build DID. The following describes the main characteristics of Indy:  
* It provides individuals with independent control over their personal data. * It has to allow interoperability with other decentralized ledgers. * It supports the attribute and claims schema system written to the ledger for dynamic discovery of claim types. Hyperledger Aries provides a library for handling verifiable digital credentials. The envelope of the messages between agents has been standardized in the form of the DIDComm protocol. DIDComm describes how messages should be encrypted and decrypted in transport. The agent is an entity working in the cloud CDM, where it interprets messages on behalf of its organization and executes a command to support secure access to the CDM service. The agent has secure storage that is used for all the information collected by it. In this paper, we design a researcher as one of agents in the cloud CDM. In summary, in terms of information security, identity management plays an important role in preventing illegal access from the outside. However, the traditional identity management model relies on a third-party central system for information management. Figure 1: The DID model proposed by W3C. In this approach, it is difficult for the central system to have complete reliability, and it involves the problem of information exposure to the outside. Identities must not be held by a single third-party, even if it is a trusted entity temporally [32; 33]. Additionally, the central system has a single fault risk [34; 35]. To solve the above problems, the proposed model is based on SSI, where individual researchers maintain their identity, and supports secure CDM data transmission and solves the privacy problem. The proposed model is used for safe CDM data transmission and access control of transmitted data in the cloud CDM environment. Table 1 compares the traditional identity management technology and the DID in the following five aspects. * Privacy and protection The rights of users must be protected on the set of tasks such as handling data. The users must be able to choose their privacy model. When personal data are disclosed, that disclosure implicates the minimum amount of information required to complete the given task. * User control and consent In the cloud CDM, researchers must control their identities. They may enable referring to their own identity, updating it, and accessing their own data. Their identities must not be held by a single third-party entity in the cloud CDM. * Dependency Each of the organizations is running an independent corporation without dependency in the cloud CDM. * Fault tolerance To access a system handling user identity, it enables the continued working of the system despite failures or malfunctions in cloud CDM. * Usability The access right is a system granted to users according to the domain policy. The researcher's experience must be consistent with their expectations in a research process.