To address privacy concerns, data in the blockchain should be encrypted in advance to avoid data access from all users in the blockchain. However, encrypted data cannot be directly retrieved, which hinders data sharing in the blockchain. Several works have been proposed to deal with this problem. However, the data retrieval in these schemes requires the participation of data owners and lacks finer-grained access control. In this paper, we propose an attribute-based keyword search scheme over the encrypted blockchain, which allows users to search encrypted files over the blockchain based on their attributes. In addition, we build a file chain structure to improve the efficiency of searching files with the same keyword. Security analysis proves the security of the proposed scheme. Theoretical analysis and experimental results in performance evaluation show that our scheme is feasible and efficient.

Blockchain; searchable encryption; attribute-based encryption; smart contract