Recently, distributed online social networks (OSNs) are developed to address the security and privacy issues in centralized OSNs. Identity based cryptography (IBC) was introduced into distributed OSNs recently for better identity verification and authentication purposes. However, current IBC-based solutions in OSNs could not address the problem of secure private key issuing. In this paper we propose PEKING: a novel Pivacy Enhanced Key IssuiNG scheme for distributed online social networks using IBC. Our scheme adopts key generate center (KGC) and key privacy assistants (PAs) to issue keys to peers securely. In the scheme, PAs can be selected from users' friends. Neither KGC nor PAs can impersonate the users to obtain the private keys. Furthermore, to maintain the security of PAs, we develop a scheme to authenticate PAs using Byzantine fault tolerance protocol. The experimental results show that PEKING performs effectively and efficiently, and is able to support large scale networks.