Abstract
In Online Social Network (OSN) one of the major attacks is Sybil attack, in which an attacker subverts the system by creating a large number of pseudonymous identities (i.e. fake user accounts) and using them to establish as many as possible of friendships with honest users to have disproportionately large influence in the network. Finally, the Sybil accounts led to many malicious activities in the online social network. To detect these kinds of fake accounts in online social network is a big challenge. In this paper, we propose a prevention mechanism for Sybil attack in OSN based on pairing and identity-based cryptography. During the formation of a group when any user wants to join the group, a user needs to pass a trapdoor which is built based on pairing-based cryptography and consists of a challenge and response mechanism (process). Only the authenticated users can pass the trapdoor and the fake users cannot pass the process, therefore, exclusively the genuine users can join a group. Thus, the Sybil nodes would not be able to join the group and the Sybil attack would be prevented in the OSN.