## 2 Identity Model
The service provider offers the service based on the received validation results after the identity provider returns the authentication results. 1. IdP: persists user identity, authenticates and authorizes incoming requests. 2. SP: Has resources. Access to the resources is restricted by IdP. 3. Subject: Has a credential used for authentication. Subjects serve as the system's main facilitators, utilizing the numerous services provided by the service provider and identity provider. Type of Identity Management (IdM) can be classified into three models: Isolated IdM, Centralized IdM, and Federated IdM [7]. Table 1 shows the types of IdM. In the Isolated IdM model, also called the Silo model, each service provider has its own IdP. The identity provider and service provider are mixed up and they share the same space. The end user should log in for each service provider with a different identity. The intricacy and inadequate scalability innate to the isolated Id management model leads to relying on the third-party authentication scheme [10]. The identity is handled for each service, and the user needs to register his/her identity with personal information and then to perform a specific authentication process for each service. For user authentication and access control of the cloud CDM service, an identity management system is established and operated with high management cost, because the users of the cloud CDM must perform identity registration separate identifiers for each service. In the centralized IdM Model, IdP is based on centralized digital identity management. The end user can log in and access with a single user identity. The user registry is managed by third-party services that contain identity information for participants in the cloud \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Isolated IdM** & **Centralized IdM** & **Federated IdM** \\ \hline Identity Management Autdoriy & Service provider & Centralized identity management server & User-selected identity provider \\ \hline Registration of & User-attribute registration & Central identity server & Pre-registration wild IdP as \\ Identity information & by service & & federation service user \\ \hline Privacy preserving & Privacy-leak problem & Privacy-leak problem & Privacy-leak problem \\ \hline Fault & Single-point failure & Single-point failure & Single-point failure \\ \hline Level of scalability & Low & Low & Middle \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of IdM. Figure 1: Traditional identity management architecture. CDM. All of the access controls in all the SPs are controlled by a single access control list (ACL); hence, the users' identities and passwords can be used to authenticate themselves with SPs. The centralized model is weak as it runs the risk of having one identity and having its related credential disclosed. The centralized IdM Model is used to handle access control in one environment. A centralized identity management system empowers teams with visibility so they can detect and respond to threats swiftly and efficiently. It centrally manages reliable user identities and, compared with the isolated type, the establishment and operation of the identity management system is more efficient. Several services connected by authentication are available. With these technical characteristics, the centralized type is suitable for providing multiple services through a single cloud CDM. However, when the central management system fails, it is impossible to use the entire service and there are limitations in interoperability and scalability due to the closed structure. The service provider has to decide whether the cloud CDM should be usable in an inter-institute context in the cloud service. From the point of view of a service provider, it is important to support the ease of deployment of the identity system, preserving privacy.