The development of cloud-assisted electronic health system effectively addresses the drawbacks of traditional medical management system. However, some challenging problems such as security and privacy in data storage and sharing cannot be ignored. First, it is difficult to ensure the integrity of electronic health records (EHRs) during the data outsourcing process. Second, it is difficult to guarantee the privacy and traceability of EHRs during the data sharing process. In this paper, a blockchain-based eHealth system called BCES is proposed to ensure that the manipulation of EHRs can be audited. In BCES, each legitimate query manipulation of data consumers, together with each legitimate outsourcing manipulation of hospitals, will be written into the blockchain as a transaction for permanent storage, which ensures the traceability. At the same time, the attributes-based proxy re-encryption is adopted to achieve fine-grained access control of medical data, and any behavior that threatens the integrity of EHRs will be discovered by the auditor. Due to the traceable and tamper-resistant characteristic of blockchain, any entity that had an illegal manipulation of EHRs will be held accountable to the evidence of our constructed Proof-Chain. Finally, security analysis and performance evaluation demonstrate that this scheme is secure and efficient.

云辅助电子医疗系统的开发有效地解决了传统医疗管理系统的弊端。但是，一些具有挑战性的问题，例如数据存储和共享中的安全性和隐私性，不容忽视。首先，在数据外包过程中很难确保电子健康记录（EHR）的完整性。其次，很难在数据共享过程中保证电子病历的私密性和可追溯性。在本文中，提出了一种称为BCES的基于区块链的eHealth系统，以确保可以对EHR的操作进行审计。在BCES中，数据消费者的每项合法查询操作以及医院的每项合法外包操作都将作为永久存储交易写入区块链中，以确保可追溯性。同时，采用基于属性的代理重新加密来实现对医疗数据的细粒度访问控制，审核员将发现威胁EHR完整性的任何行为。由于区块链的可追溯性和防篡改特性，任何非法操纵电子病历的实体都将对我们构建的证明链的证据负责。最后，安全分析和性能评估表明该方案是安全有效的。任何非法操纵电子病历的实体都将对我们构建的证明链的证据负责。最后，安全分析和性能评估表明该方案是安全有效的。任何非法操纵电子病历的实体都将对我们构建的证明链的证据负责。最后，安全分析和性能评估表明该方案是安全有效的。