To solve the problems such as data sharing difficulty, data privacy disclosure of data sharing between medical institutions, a blockchain-based Electronic Health Record (EHR) sharing scheme was proposed. Firstly, based on the blockchain characteristics of non-tampering, decentralization and distributed storage, a blockchain-based EHR data sharing model was designed. The blockchain network and distributed database were used to jointly store the encrypted EHR and the related access control policies, preventing the modification and leakage of EHR data. Secondly, the Distributed Key Generation (DKG) and Identity-Based Proxy Re-Encryption (IBPRE) were combined to design a data secure sharing protocol. The Delegated Proof of Stake (DPOS) algorithm was used in this protocol to select the proxy node, which re-encrypted the EHR to achieve the data sharing between single pair of users. The safety analyses show that the proposed scheme can resist the fake identity and the replay attack. Simulation experiments and comparative analyses show that DPOS algorithm has the efficiency higher than Proof of Work (POW) algorithm, and slightly lower than the Practical Byzantine Fault Tolerance (PBFT) algorithm, but the proposed scheme is more decentralized and costs less computing power.

The security problem of the data stored in the cloud is a challenge for cloud computing. Encryption is the main method to solve the problem of data storage security in cloud computing. The confidentiality issue of the encryption is the key management. The attribute-based encryption and re-encryption scheme in cloud computing was proposed. It combined attribute-based encryption and re-encryption technology. The cloud server could re-encrypt for different users, and re-encrypt for a group of users at a time. Thereby the scheme reduced the number of re-encryption keys. The data owner could generate and send the keys of re-encryption for a group of users and the data requester could use the key corresponding to the attribute set to decrypt the data of several data owners, which reduced the amount of keys’ transmission. The scheme reduced the difficulty of key management and improved the efficiency of the scheme. In the end, the security and efficiency of the scheme were discussed.