Keeping identity secret in online social networks

In this paper, we construct a system which can hide users' identity when they visit untrusted third party storage sites. We also define a fine-grained access control policy for the data owner to freely define who can access the record. That is to say, the data owner divide his friends into several groups and issues them corresponding credentials for accessing his data. However, he can adds a friend at any time in a revocation list (RL) so that that friend could not access the data owner's data any more even if he has credentials. We theoretically prove the security of our protocols, and evaluate the performance of our protocols through simulations.