Abstract: When sharing medical data, the volume of shared data often exceeds the necessary amount, leading to significant computational overhead when encrypting a large number of metadata. This paper proposes a medical data classification encryption and sharing scheme based on blockchain, which integrates attribute-based encryption and blockchain to facilitate access control and data sharing of medical information. First, the entire medical dataset is classified into medical metadata according to the basic information, medical departments and disease types, enabling fine-grained access control. Then, a data access strategy classification algorithm is proposed, which divides the data access strategy into attribute encryption strategy and blockchain access strategy. Multiple attribute encryption strategies are combined to reduce the computational cost of constructing the access structure tree. Smart contract controls the access of the data on the chain according to the blockchain access policy, and the authority is revoked by modifying the blockchain policy. Finally, the security analysis and simulation experiments validate the feasibility and efficiency of the proposed scheme.

Key words: blockchain, attribute-based encryption, smart contract, access control, data sharing