Social Networking sites nowadays use passwords to authenticate users. But there are certain problems with this; the user may forget his password or the account may be hacked by the attacker. The web services nowadays provide users' with an alternative email address or security question to recover password. Unfortunately, this authentication mechanism is insecure or unreliable. To overcome the drawbacks of this mechanism, a backup mechanism for account recovery is considered. Backup authentication mechanism helps the users' to regain accounts with the help of trusted friends. In this mechanism user depends on multiple trustees and recover their account via verification mails. A trust model which is implemented in social networking sites is associated with an authentication protocol. Trust evaluation models are really needed in smart environments is that they create a secure yet more flexible environments because security policies cannot do that. Trust systems are very adaptive to the user needs, actions and behaviors.
Sagar, K., & Waghmare, V. (2016). Measuring the Security and Reliability of Authentication of Social Networking Sites. In Procedia Computer Science (Vol. 79, pp. 668–674). Elsevier B.V. https://doi.org/10.1016/j.procs.2016.03.085