Coarser-Grained Multi-user Searchable Encryption in Hybrid Cloud

The task of searchable encryption schemes in multi-user setting is to handle the problem of dynamical user injection and revocation with consideration of feasibility. Especially, we have to make sure that user revocation will not cause security problem, such as leakage of secret key. Recently, fine-grained access control using trusted third party is proposed to resolve this issue. However, it increases the management complexity for maintaining massive authentication information of users. We present a new concept of coarse-grained access control for the first time and use it to construct a multi-user searchable encryption model in hybrid cloud. In our construction, there are two typical schemes, one is broadcast encryption BE scheme to simplify access control, the other is a single-user searchable encryption scheme, which supports two-phases operation and is secure when untrustful server colludes with the adversary. Moreover, we implement such a practical scheme using an improved searchable symmetric encryption scheme, and security analysis support our scheme.