Multilevel Data Security and Revocability in Cloud Storage System

In this paper, we propose a data security protection mechanism with revocability for cloud storage system. An encrypted message is send from the sender to receiver through a cloud storage server. The sender only knows the identity of the receiver. The receiver's certificate or its public key is not known to the sender and also the receiver has two things in order to decrypt the ciphertext. The secret key is stored in the computer and the unique personal security device which connects to the computer. It is impossible to decrypt the cipher text without both the key. Once the Security device is lost, the device is revoked. Since revoking has been done the ciphertext cannot be decrypted. This can be achieved by some algorithms to change the existing ciphertext to be un-decrypt able by this device.