Two Dimensional Security in Cloud Data Sharing with Factor Revocability Mechanism

In the two dimensional security in cloud data sharing with factor revocability mechanism. This system allows a sender to send an encrypted message to a receiver through a cloud storage server. The sender only needs to know the identity of the receiver but no other information (such as its public key or its certificate). The receiver needs to possess two things in order to decrypt the cipher text. The first thing is his/her secret key stored in the computer. The second thing is a unique personal security device which connects to the computer. It is impossible to decrypt the cipher text without either piece. More importantly, once the security device is stolen or lost, this device is revoked. It cannot be used to decrypt any cipher text. This can be done by the cloud server which will immediately execute some algorithms to change the existing cipher text to be un-decryptable by this device. This process is completely transparent to the sender. Furthermore, the cloud server cannot decrypt any cipher text at any time. The security and efficiency analysis show that our system is not only secure but also practical.