A revocable attribute-based encryption EHR sharing scheme with multiple authorities in blockchain.

With the development of digital healthcare, sharing electronic medical record data has become an indispensable part of improving medical conditions. Aiming at the centralized power caused by the single attribute authority in current CP-ABE schemes and the problem that cloud servers are curious and even malicious, we design a revocable CP-ABE EHR sharing scheme with multiple authorities (MA-RABE) in blockchain. In this solution, a group of authorities complete user attribute distribution, key generation and user management through secret sharing and transactions. Besides, we innovatively implemented a distributed one-way anonymous key agreement so that other participants cannot obtain useful information from the fully hidden policy embedded in the ciphertext. Taking into account the computational overhead of a large number of bilinear operations in the decryption process, the solution also supports the cloud server to pre-decrypt the ciphertext, and the data user only needs to perform exponentiation operation once to obtain the plaintext from the pre-decryption result. Theoretical analysis and performance evaluation show that the scheme has reliable security and lower user revocation and ciphertext update overhead.