As a characteristic cloud application an organization pledge the cloud services and approves its team to share files in the cloud. Each file is explained by a set of keywords and the staff as authorized users can repossess files of their interests by querying the cloud with certain keywords. In such an environment how to protect user privacy from the cloud which is a third party outside the security boundary of the organization turn into a key problem. The communication cost acquires on the cloud will also be concentrated since files shared by the users need to be returned only once.