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. Proxy re-encryption is a kind of secret sharing method, but it is different from secret sharing in common meaning. In general, secret sharing 1 refers to the split of secrets into several shares, and each share is managed by different participants. A single participant cannot recover secret information. Only a number of participants can work together to recover secret messages. Typical schemes are secret sharing schemes SSSs 2-4 and multi-secret sharing schemes (MSSSs) 5-7. Proxy re-encryption is a new secret sharing method in cloud environment. The classical proxy re-encryption adds a proxy to the traditional public key encryption system. On the basis of the authorization of Alice (Alice give a conversion key to the proxy), the proxy can convert the cipher-text of Alice's data into the cipher-text of Bob without decryption, and the proxy cannot obtain the plain-text of Alice's data. This not only protects the key of Alice, but also ensures the security of Alice's data. The concept of proxy re-encryption is proposed by Blaze, Bleumer and Strauss 8 on Eurocrypt'98. In fact, proxy re-encryption does not need to re-encrypt, only the cipher-text is converted simply. Therefore, proxy re-encryptionis also called proxy conversion encryption. In 2005, on ACM CCS 2005, Ateniese, Fu, Green and Hohenberger gave the formal definition of their specification and proposed the first proxy re-encryption scheme 9. This scheme is a two-way authorized proxy re-encryption scheme. That is, the proxy can transform not only the cipher-text of Alice's data into the cipher-text of Bob, but also the cipher-text of Bob's data into the cipher-text of Alice. Later, Ateniese, Fu, Green and Hohenberger proposed a one-way authorization proxy re-encryption scheme 10. At the annual meeting of CCS 2007, Canetti and Hohenberger proposed a scheme of proxy re-encryption copywriting against sel...
