## 4 SSHies: An Era of Research
### Blockchain and Smart Contracts-Based Techniques in HIE Systems: A Background
The study concluded that blockChain containers running on multiple ports are proposed for holding patient's medical records effectively. The authors of [86] proposed a secure and reliable data exchange architecture for the cyber-physical healthcare industry using blockchain technology. The methodology includes BigchainDB, Tendermint, Inter-Planetary-File-System IPFS, MongoDB, and AES encryption algorithms. The proposed system uses sensors to monitor patients, upload health data, and grant access to records to an API. Tendermint stores large data off-chain into IPFS and commits transactions on the blockchain into Tendermint. The blockchain-assisted secure and reliable data exchange architecture for Cyber Physical Healthcare 4.0 aims to address issues like data fragmentation, leakage, and illegal access to patient data. The study in [87] used a healthcare blockchain, which is a Merkle tree-based structure with leaf nodes representing patient record transactions. Transaction reference FHIR resources are recorded via URLs, keeping sensitive patient data out of the blockchain. The blockchain algorithm adds data to the blockchain, and mining ensures interoperability by avoiding the drawbacks of the PoW consensus algorithm. The study also discusses data discovery and access, ensuring that external entities can query the blockchain using keywords in the secure index field. The authors conclude that blockchain can play a crucial role in enabling data sharing within a network and introduce a new consensus algorithm for data interoperability. The authors of [67] proposed a blockchain called SPChain to address privacy leakage in permissioned blockchain and scalability issues in open blockchain. The proposed model includes cryptographic hash functions, chameleon hash functions, and proof-of-reputation. SPChain aims to ensure confidentiality, patient-centric sharing, quick retrieval, and label and correctness. It also resists blockchain attacks, such as 51% attacks, selfish mining attacks, Sybil attacks, and SPCChain attacks, such as reputation fraud and inhibition attacks. The construction of SPChain includes three types of transactions: register transaction, medical transaction, and label transaction. The chain structure stores register transactions in key-blocks, and the consensus mechanism creates the reputation algorithm and transaction processing algorithm. The authors of [88] devised a health-related data sharing system that integrates IoT and distributed ledger technology (DLT) to facilitate secure, fee-less, tamper-resistant, highly scalable, and granularly controllable health data exchange. They employed wearable devices and stationary air quality sensors, IOTA's distributed ledger, directed acyclic graph tangle for data sharing, masked authenticated messaging (MAM) for data communications, and Merkle hash tree for data encryption and verification. The prototype was utilized for the remote diagnosis of tremor disease, demonstrating costless data integrity and flexible access management during data sharing. Furthermore, the study revealed the feasibility of fully decentralized health data sharing by substituting local servers with edge computing devices. In [64], the proposed medical record system based on blockchain aims to leverage clouding technology for storage and implement smart contracts and a consensus algorithm for electronic medical records (EMRs). The system comprises several components, including a central authority, a management system (CAMS), a list of service providers, a data lake pool, hash generators, and a cloud server. Employing a permissioned blockchain model, the system allows only verified and authenticated users to generate data and participate in the data-sharing process, ensuring confidentiality. Its architecture is interconnected through a decentralized peer-to-peer model. The authors of [89] proposed a privacy-preserving scheme for medical data sharing among medical institutions and users using K-anonymity and searchable encryption techniques.