## 4 SSHies: An Era of Research
### Blockchain and Smart Contracts-Based Techniques in HIE Systems: A Background
The experiment illustrates the non-repudiation aspect of blockchain and an integrated architecture for information security protection and data verification. The study in [78] aimed to improve medical diagnosis by ensuring robust, efficient, and accurate access to a patient's full medical history. The study concluded that the specific role of blockchain technology in healthcare systems remains uncertain. However, it utilized a vignette-based experiment to explore the potential correlations between non-blockchain systems and blockchain-based systems regarding patients' perceptions of security and their motivations to share health records within a healthcare provider's information system. The authors of [79] proposed an efficient access control system for privacy-sensitive medical data, allowing data owners to specify their preferred access controls. The system involves establishing specific access policies through Health Wallet, which were then registered by patients as a form of transmission within the BC network's policy chain. Data storage and retrieval involve encrypting data using a symmetric encryption technique, such as AES, and sending EncrpData (id, data) to the Inheritance Management (IHM) that sends a message to confirm data receipt. The study concluded that the health chain is suitable for use in smart healthcare systems, as demonstrated by experimental data and security analyses. The authors of [80] introduced a permissioned blockchain model to enhance the security and efficiency of sharing electronic health record data. Their proposed methodology comprises three layers within the blockchain architecture: a decentralized storage layer, a blockchain layer, and a user layer. In this framework, encrypted data are stored and indexed using associated hashes in the decentralized storage layer, while the blockchain layer employs the IBFT consensus algorithm and smart contracts. The user layer features a public-private key pair for transaction signing and a unique address for user identification on the blockchain. Results indicated that the proposed system outperformed existing blockchain-based solutions across different network sizes, demonstrating superior security and data integrity. The study of [81] aims to combine attribute-based encryption (ABE) and blockchain-assisted SABE with hidden policy support to achieve data confidentiality, security under keyword attacks, and fine-grained access control. The proposed framework includes three phases: setup, key generation, and trapdoor generation. It ensures security through controlled searching, query privacy, and semantic security against chosen keyword attacks. The results showed that the framework is very efficient in terms of time cost, with the setup, key generation, and trapdoor generation times being very low compared to other approaches. In [82], the OmniPHR model is a distributed architecture that integrates Patient Health Records (PHRs) for patients and healthcare providers. The model consists of multiple modules: a data block and service module, which handles interoperability; a distributor that distributes and replicates data blocks; a validator that checks data block integrity; a node manager that manages input and output of routing overlay nodes; and a message router that provides communication services. The security and privacy module handles privacy and security tasks, including encryption, digital signatures, authentication, and roles and privileges. The model showed that even with an increase in nodes and messages, latency remains stable, demonstrating that OmniPHR can support a growing number of nodes and requests without significantly increasing delivery time. The authors of [62] have developed a prototype implementation and evaluation of a PHR model that integrates distributed health records using blockchain technology and the penEHR interoperability standard. They used the OmniPHR architecture model, which supports the implementation of a distributed and interoperable HR.