A Blockchain-Based Framework for Securing Cloud-Based Electronic Health Records Using Smart Contract Access Control, IPFS and Elliptic Curve Cryptography

Cloud computing enables healthcare organizations to store and share electronic health records (EHRs) at low cost, but centralized cloud storage exposes sensitive patient data to unauthorized access, tampering, single points of failure and dependence on trusted third parties. This paper proposes a novel approach for securing cloud-based EHR systems using blockchain technology. The framework combines a smart-contract-based access control model managed by an EHR manager and a policy store, a decentralized storage layer based on the InterPlanetary File System (IPFS) with a distributed hash table (DHT), and elliptic curve cryptography (ECC) for encrypting patient records with short keys suitable for resource-constrained devices. The data uploading and data sharing phases are specified, together with a use-case model involving healthcare providers, cloud service providers and end users. Network performance is modelled in terms of file loss and total transmission time, and security is analysed through the probability that an attacker obtains all replicated file blocks and the probability that an attacker controlling part of the network rewrites the chain. The analysis shows that the attack success probability falls below 0.1% after five confirmation blocks when the attacker controls 10% of the computing power. The prototype, implemented on Ethereum with Solidity smart contracts, Remix IDE, web3js, Infura and JSON-RPC, and audited with SmartCheck and Oyente, supports registration, key generation, encrypted upload, block creation, user verification, secret key verification and decryption. A comparison with four existing schemes shows that the proposed system is the only one that satisfies all seven criteria of confidentiality, availability, decentralized access, authorization, user authentication, integrity and privacy, while achieving lower network latency for 100 to 500 users.