In opportunistic Networks, compromised nodes can attack social context-based routing pro-tocols by publishing false social attributes informa-tion. To solve this problem, we propose a security scheme based on the identity-based threshold sig-nature which allows mobile nodes to jointly gener-ate and distribute the secrets for social attributes in a totally self-organized way without the need of any centralized authority. New joining nodes can reconstruct their own social attribute signatures by getting enough partial signature services from en-counter opportunities with the initial nodes. Mobile nodes need to testify whether the neighbors can provide valid attribute signatures for their routing advertisements in order to resist potential routing attacks. Simulation results show that: by implemen-ting our security scheme, the network delivery probability of the social context-based routing pro-tocol can be effectively improved when there are large numbers of compromised nodes in opportun-istic networks.