Cloud computing strengthens its presence in the public sector, organizations and individuals are looking for cloud services to improve productivity, security and reduce costs. Apart from communication, file storage is the main requirement for common people. Traditional data centers consist of large collections of server farms implementing perimeter-security measures. Public cloud offers a multitenant service, in which the concept of the network perimeter evaporates. For the former concern, data encryption before outsourcing is the simplest way to protect data privacy.