A Quantum secure sharing protocol for Cloud data based on proxy re-encryption.

A quantum scheme for cloud data sharing based on proxy re-encryption is proposed. The user Alice stores the cipher-text of her data on cloud data center. When Alice wants to share her data with another user Bob, Alice is called the delegator and Bob is called the delegatee. The cloud service provider (called the proxy) can convert the delegator's cipher-text into the delegatee's cipher-text without decrypting the former, so that the delegatee can get the plain-text of Alice's data with his private key. The proxy cannot obtain the plain-text of the user's data stored on cloud data center. Delegator in the protocol should have the ability of producing Bell states, performing Bell basis and Z-basis measurements, and storing qubits. The quantum requirements for the delegatee are reduced. The delegatee needs to have the ability of reflecting and performing Z-basis measurement. One secret at a time (one-time one-pad) is theoretically implemented, especially when the same data is shared multiple times. The anti-selection plain-text attack security and the anti-selective cipher-text attack security are realized. Fine-granularity secret data sharing is achieved flexibly.