With many features of cloud computing, many organizations have been considering moving their information systems to the cloud storage. Cloud storage is a service model, in which data is stored, maintained, managed and backup remotely, and made available to the users over the network. However, an important problem in public cloud is preserving confidentiality of stored data from both unauthorized access and the storage provider i.e. cloud. So, in order to make confidentiality the data owners first encrypts the file before uploading them on the cloud storage, and re-encrypting whenever user credentials change.