Keyword search over encrypted cloud data based on blockchain in smart medical applications

In consideration of the inconvenience of sharing user identity authorization, and the lack of correctness verification for searching electronic medical records in hospitals under the many-to-many search model, we propose an blockchain-aided searchable attribute-based encryption scheme that supports verification, we apply the scheme to electronic health record systems. Using blockchain technology, the ciphertext document is stored in the medical cloud, the secure index is stored in the blockchain, and the smart contract is used for searching, which reduces the computational burden of the medical cloud. In addition, this scheme can verify whether the results returned by the cloud server are correct, ensure data integrity and confidentiality. The scheme eliminates duplicate data and reduces the storage space of the medical cloud. Furthermore, users’ privacy security is guaranteed due to the hiding of access policy. The security analysis shows that the proposed scheme satisfies the semantic security of adaptively chosen-keyword attacks, can effectively protect the confidentiality of medical data and anonymity of users. Performance analysis and experiments demonstrate that the proposed scheme achieves optimizations in security index generation, trapdoor generation, search efficiency and result verification; hence, it is more suitable for many-to-many search scenarios such as smart medical applications. It effectively realizes the sharing of patient electronic medical records between doctors and third-party users without infringing on patient privacy.