Privacy preserving cloud data sharing system with flexible control

With the development of cloud technology, sharing date between users securely becomes more and more important. Moreover, the cloud server should provide a flexible control on sharing date. This work presents a notion named fuzzy conditional broadcast proxy re-encryption (FC-BPRE), in which a semi-honest proxy can transform a delegator's ciphertext to a new ciphertext for a set of delegatees when the ciphertext satisfies a certain condition set by the delegator. However, the proxy cannot learn any useful information about the underlying plaintext. The proxy can convert a ciphertext, encrypted under a condition set W, to a ciphertext encrypted under a condition set W′ using a broadcast re-encryption key, if and only if S and S′ are close to each other. We first formalize the notion of FC-PBRE scheme and then proposed a construction.