There still remain problems associated with security in patients’ data as used in EHR systems, such as privacy concerns, data integrity issues, or unauthorized access. This work introduces a new key management solution between patients and doctors in a B&C EHR system. Thus, we propose a combination of blockchain technology and cloud computing as the basis of the developed hybrid architecture. Our approach protects data sharing through asymmetric encryption and smart contracts and distributes key management. In this work, we deploy and test the above-proposed system on a private Ethereum blockchain environment in a secure cloud environment. Earlier this year, the health information exchange reduced unauthorized access attempts by 9 percent compared to traditional EHR systems. The experimental results on the blockchain access control mechanism showed that the rate of successfully preventing data tampering reached 95%, although the number of average transactions per second was around 0.5 s. In addition, our key management protocol reduced the number of reported key compromises by 87% compared to the centralized model. Consequently, when EHR systems are implemented using blockchain and cloud integration with the key management strategy that we have proposed, it reveals a highly efficient and secure patient data management system. This approach not only improves data privacy and accuracy, but it also promotes patient-centered health care because people will have ownership of their own data.