A distributed computer network is a special type of network, which facilitates the customers to use different network services which is provided by the service providers. In the distributed computer networks, user verification is an important process for the security. In the verification process, the decision is taken whether the user is legal or illegal and after that allow the users to access the service. A new certification scheme which is called as Single sign-on mechanism that facilitates

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... he users with a single credential to be verified by multiple service providers. In addition to the user verification, service provider's verification is also important to evade bogus servers. After completion of the user and service provider verification, a session key is provided to maintain the confidentiality of the data exchange between a user and a service provider. In this survey, different mechanisms are suggested for providing the anonymity of legal users. Chang and Lee scheme is one of the single-sign on methods which is presented by Chang and Lee for providing security in the distributed computer networks. But this scheme has two impersonation attacks. The drawbacks are identified in the Chang and Lee scheme and use another single sign-on scheme which is called Hsu and Chuang scheme which stimulated the design of the Chang-Lee scheme. Particularly, in this survey investigate the different single sign-on mechanisms to meet credential privacy and reliability of authentication.