A Fine-grained Conditional Proxy Broadcast ReEncryption Policy for File Sharing System

With the proliferation of electronic devices, cloud storage has become an integral part of synchronizing files between devices. However, data stored on the cloud is vulnerable to unauthorized access during the sharing process. The traditional conditional proxy broadcast re-encryption solution is suitable for the above application scenarios but does not support flexible control of conditions. This article describes the concept of fine-grained conditional proxy broadcast re-encryption (FGC-BPRE). The scheme utilizes an access tree to generate a re-encryption key. If the ciphertext keyword satisfies the conditions in the access tree, the proxy can convert the user's ciphertext into a new ciphertext for a group of users. In addition, this paper also constructs a fine-grained conditional proxy broadcast re-encryption scheme and verifies the security of selective ciphertext attacks without oracles.