Cloud computing has been envisioned as the next generation architecture of IT Enterprise Cloud computing moves the application software and databases to the large data centers, where the management of the data and services may not be fully trustworthy. This unique attribute, however, poses many new security challenges which have not been well understood. In this paper, the authors focus on cloud data storage security, which has always been an important aspect of quality of service. To ensure the correctness of users' data in the cloud they propose providing security using GDC. Public-key digital certificate has been widely used in Public-Key Infrastructure (PKI) to provide user public key authentication. However, the public-key digital certificate itself cannot be used as a security factor to authenticate user.