## 4 SSHies: An Era of Research
### Blockchain and Smart Contracts-Based Techniques in HIE Systems: A Background
EHR data are encrypted and stored off-chain in Health Insurance Portability and Accountability Act-compliant cloud-based storage. Public key infrastructure-based asymmetric encryption and digital signatures are used to secure shared EHR data. The study by [96] explored the potential of blockchain technology in the healthcare industry from the perspective of patients. It presents an experimental study using 16 information exchange scenarios, four exchange mechanisms, two types of health information, and two privacy policy transparency levels. The study found significant differences in patients' perceptions of various exchange mechanisms regarding privacy concerns, trust in competency and integrity, opt-in intention, and willingness to share information. Interestingly, participants held a favorable attitude towards blockchain-based exchange mechanisms for privacy protection, coordination, and information exchange purposes. The study suggests potential limitations of a blockchain-based HIE that healthcare organizations should address to ensure secure and private exchange of personal health information. The authors of [47] proposed an end-to-end framework for data trust using blockchain to offer trustworthy data sharing. The trust value is available to data users interested in a particular data set, determining the number of verifiers for verification. It is also computed based on the data owner's reputation, endorsements, and confidence. Data users ensure that the data set's quality is adaptively examined and updated. The system also provides secure and traceable access control management using smart contracts, allowing data owners to have full control over their data assets and regulate access permissions without relying on third parties. The blockchain's provenance and auditability features allow data owners to monitor access regulations and modifications on their data assets. The study [97] introduced a secure method for storing and sharing E-health data, incorporating a selective encryption algorithm, fragmentation, and dispersion. This method involves four key steps: generating E-health data, fragmenting the data into public and private fragments, and implementing access control for data sharing. The public fragment is transmitted to cloud servers, whereas the private fragment, containing crucial information, is stored on smartphones. It is encrypted and backed up on a cloud server with higher trust levels. End-users have control over data sharing of private fragments on smartphones and can decide whether to share them with medical institutes. Once authenticated, institutes can download the public fragment from the cloud server, and private fragments can be shared anonymously. The authors of [48] developed an access control framework using smart contracts and blockchain to secure the sharing of EMRs among various entities. The framework includes hospitals, patients, smart healthcare devices, medical central units (MCUs), cloud servers, a blockchain network, and SCs. The smart contract-based mechanism allows patients to be the real owners of their EMRs and securely share them. The framework uses four SCs: validation contract (VC), get access contract (GAC), grant contract (GC), and revoke contract (RC). The proposed architecture involves uploading EMRs from patients to hospitals, encryption of EMRs on a cloud server, and verification of access requests from hospitals. The SC-based access control policies check authentication and send the result to the blockchain. The study in [98] focused on the application of blockchain technology in stroke nursing information management systems using AI. The system involves sending patient medical data, such as treatment, EMR, PHR, and EHR, to the cloud, forming blocks in the blockchain phase. Hospitals are equipped with wireless sensor networks (WSN) for data sharing. Lightweight deep learning models and natural language processing (NLP) algorithms are used to transfer written and typed medical information to the blockchain.