Abstract: Opportunistic networks integrate the concepts of delay-tolerant networks, mobile ad-hoc networks and social networks. In opportunistic networks, the information can be transmitted and shared by the parallel opportunistic contacts between different mobile users without any pre-existing internet architecture. The social context information is exploited to formulate the routing and forwarding strategies which can improve the network performance efficiently in comparison with the traditional routing protocols. However, privacy is a primary challenge in opportunistic networks, for some social context information is sensitive and users dont want to expose such information to unfamiliar nodes. We propose a security scheme based on IBE (identity-based encryption) to protect the privacy of nodes and confidentiality of messages for social context-based routing in opportunistic networks. The efficient-PEKS (public key encryption with keyword search) is used to set up trapdoors for each nodes social attributes so that relay could compute the matching of social context between itself and destination node without getting any social attribute information from the destination node. Meanwhile, our scheme encrypts the messages by employing the combination of nodes social context as the public key to ensure the confidentiality. Simulation results show that implementing our security scheme does not induce any negative impact on the delivery probability and the average delay, which indicates that our security scheme is practical and effective for opportunistic networks.