The Role of Blockchain in Medical Data Sharing

: As medical technology advances, there is an increasing need for healthcare providers all over the world to securely share a growing volume of data. Blockchain is a powerful technology that allows multiple parties to securely access and share data. Given the enormous challenge that healthcare systems face in digitizing and sharing health records, it is not unexpected that many are attempting to improve healthcare processes by utilizing blockchain technology. By systematically examining articles published from 2017 to 2022, this review addresses the existing gap by methodically discussing the state, research trends, and challenges of blockchain in medical data exchange. The number of articles on this issue has increased, reﬂecting the growing importance and interest in blockchain research for medical data exchange. Recent blockchain-based medical data sharing advances include safe healthcare management systems, health data architectures, smart contract frameworks, and encryption approaches. The evaluation examines medical data encryption, blockchain networks, and how the Internet of Things (IoT) improves hospital workﬂows. The ﬁndings show that blockchain can improve patient care and healthcare services by securely sharing data.


Introduction
Everyone may benefit from healthcare data.It maintains a record of our bodily characteristics.It is essential for the treatment and diagnosis of disorders [1].With the fast growth of artificial intelligence (AI), health records have become a tremendous advantage.It may assist in the development of AI diagnostic models and aid in the diagnosing process.Even while the recording of medical data has moved from paper data to electronic medical records (EMRs), which are more convenient for data storage and access, more attention needs to be placed on data privacy [2].Several institutions and hospitals have curtailed data transmission and exchange to prevent data privacy breaches, which has resulted in the establishment of data silos as medical information is dispersed among numerous healthcare institutions [3].
The sharing of medical data provides numerous benefits to diverse stakeholders.Sharing data among clinical organizations, hospitals, and healthcare providers, for example, improves patient care coordination by providing comprehensive medical histories, allowing for more informed decisions and preventing unnecessary testing [4].In emergencies, data sharing between hospitals and emergency medical services can expedite care, as immediate access to vital patient information enables responders to administer appropriate treatment, thereby reducing delays and enhancing patient outcomes [5].The integration of medical data sharing with smart homes and Internet of Things (IoT) devices enables remote patient monitoring, which is advantageous for patients with chronic conditions and enables proactive healthcare delivery [6].In addition, collaborative data sharing between institutions promotes medical research and scientific discoveries, facilitating the identification of patterns, risk factors, and the development of new treatments.the first to use blockchain technology.Therefore, introducing a coin is not required to utilize blockchain and develop decentralized apps [26].This section explains the principles of blockchain technology to facilitate a comprehension of the remainder of this article.To aid the reader in comprehending the blockchain idea, its fundamental properties and building blocks and also their subsequent importance in healthcare will be detailed in the following sections.

Blockchain
A blockchain may be described as a sequence of time-stamped and cryptographically connected blocks.These blocks are permanently and securely sealed [27].Each new block added to the end of the chain contains a reference to the content of the preceding block [28].The shareholders, known as the blockchain's nodes, are arranged in a peer-to-peer (P2P) network.Each node in the network has two keys [29]: a private key used for decrypting messages and allowing the node to read them, and a public key used for encrypting messages transmitted to the node.Hence, the public key encryption process is employed to assure the non-repudiation, irreversibility, and consistency of a blockchain [25].Messages encrypted with the accompanying public key can only be decrypted with the matching private key.The term for this idea is asymmetric cryptography.While a comprehensive explanation is beyond the scope of this study, more information may be obtained in [29].The so-called hash, which is created using a cryptographic one-way hash function, is used to connect every block on the blockchain.It also assures the block's compactness, anonymity, and immutability [30].
This leads us to the significance of network nodes.Because the blockchain system is a P2P network, a node may be considered a peer when it begins to connect and interact with other nodes in the network; hence, peer node is the correct term.A full node is, in layman's words, any computer that has the main blockchain client installed and runs a complete copy of the whole blockchain ledger [25].A user who wishes to interact with the blockchain connects to the network through a node [31].Miners are a subset of nodes since each miner needs to also run a fully functional node.Each miner is thus a node, but not every node is also a miner.This situation is known from a certain sort of public blockchain using the proof-of-work (PoW) consensus algorithm.Some forms of blockchain networks using different distributed consensus mechanisms, such as proof-of-stake (PoS), do not need mining [32].
Depending on the level of involvement [33], blockchain may be classified into the consortium, private, and public chain.As its name suggests, a public chain is entirely public and open to anybody.Due to the immutability of the data on the chain, public chains are regarded to be entirely decentralized.Participation in the consortium chain is restricted to authorized members, and the write/read rights and participation accounting permissions on the blockchain are constructed by the alliance's norms.The private chain is exclusive to private organizations, and the write and read rights on the blockchain, as well as the permissions to participate in accounting, are constructed by the norms of the private organization.Participating nodes are restricted in reference [34].

Smart Contracts
Computer protocols known as "smart contracts" allow for the informational distribution, validation, and enforcement of contracts [35].Smart contracts do not need the verification of a third party, and successful transactions are irrevocable and traceable.Computer software is used to create a legally binding contract that can be automatically executed.A smart contract is a program placed on the blockchain that guarantees the safety and security of transactions in the absence of third-party monitoring [36].The process of smart contracts is shown in Figure 1.In the smart contract code, predefined response rules and trigger situations are encoded, triggering specific actions automatically when predetermined conditions are met.This eliminates the need for intermediaries and improves the contract execution process's transparency, security, and efficiency.When trigger situations, such as specific dates, events, or conditions, occur, the smart contract implements predefined actions, such as transferring ownership, releasing funds, and updating records.By incorporating blockchain technology into smart contracts, participants gain an increased trust, lower costs, and reduced fraud risks.Combining blockchain technology and smart-contract streamline processes optimizes contract administration and provides a secure and transparent solution for a variety of industries.and trigger situations are encoded, triggering specific actions automatically when predetermined conditions are met.This eliminates the need for intermediaries and improves the contract execution process's transparency, security, and efficiency.When trigger situations, such as specific dates, events, or conditions, occur, the smart contract implements predefined actions, such as transferring ownership, releasing funds, and updating records.By incorporating blockchain technology into smart contracts, participants gain an increased trust, lower costs, and reduced fraud risks.Combining blockchain technology and smart-contract streamline processes optimizes contract administration and provides a secure and transparent solution for a variety of industries.Table 1 displays the highlights of blockchain-enabled smart contracts.

Features Description
Untamperable Smart contracts cannot be changed after deployment.Like a contract, this cannot be changed once signed.
Low cost Smart contracts do not need a third party to enforce the code after a violation; thus, they are cheaper than regular contracts.
Open and transparent A smart contract will execute according to the design code and be transparent once deployed.

Decentralized
Computers supervise and arbitrate smart contracts without third-party involvement.

Importance of Blockchain in Healthcare
Blockchain may provide an effective, efficient, safe, and transparent method of data and information communication for all stakeholders involved in the healthcare business [37].With tokenization and smart contracts, it is possible to decrease or eliminate the preauthorization procedure in the healthcare industry [38].While connecting with multiple parties, blockchain-based systems for health documentation protect the security of an individual's data via the use of secure encryption methods [39].Using the encryption methods, smart contracts, and tokenization used in blockchain network transactions, the preauthorization method will be drastically streamlined, allowing patients to obtain essential and informed treatment more quickly.This is a consequence of the healthcare provider's ability to immediately obtain pertinent information, whereas previously, they had to rely on the patient or on files physically delivered or emailed from many sources, such as local doctors, laboratories, etc.Not only may tokenization promote a more efficient contact and communication between insurance companies and healthcare practitioners, but it can also support and enhance patient-provider dialogue.

Features Description
Untamperable Smart contracts cannot be changed after deployment.Like a contract, this cannot be changed once signed.
Low cost Smart contracts do not need a third party to enforce the code after a violation; thus, they are cheaper than regular contracts.
Open and transparent A smart contract will execute according to the design code and be transparent once deployed.

Decentralized
Computers supervise and arbitrate smart contracts without third-party involvement.

Importance of Blockchain in Healthcare
Blockchain may provide an effective, efficient, safe, and transparent method of data and information communication for all stakeholders involved in the healthcare business [37].With tokenization and smart contracts, it is possible to decrease or eliminate the pre-authorization procedure in the healthcare industry [38].While connecting with multiple parties, blockchain-based systems for health documentation protect the security of an individual's data via the use of secure encryption methods [39].Using the encryption methods, smart contracts, and tokenization used in blockchain network transactions, the pre-authorization method will be drastically streamlined, allowing patients to obtain essential and informed treatment more quickly.This is a consequence of the healthcare provider's ability to immediately obtain pertinent information, whereas previously, they had to rely on the patient or on files physically delivered or emailed from many sources, such as local doctors, laboratories, etc.Not only may tokenization promote a more efficient contact and communication between insurance companies and healthcare practitioners, but it can also support and enhance patient-provider dialogue.
The expansion of the worldwide healthcare business may be aided by blockchain technology, which can also save money and stimulate additional investment in vital resources.With so much at risk, it is inconceivable that the current inefficient, excessively bureaucratic, and failing healthcare business can continue [40].It is time for executives, practitioners, and patients to embrace the available technological and system-based innovations.
The misuse of available information prevents healthcare organizations from providing appropriate patient care and remarkably improved services.Even though these organizations are economically competent, they are unable to meet the needs of patients.Here are a few facts from Supporting Materials that illustrate this reality.Nowadays, healthcare data breaches in organizations are estimated to cost around USD 380 per compromised record.This amount is anticipated to increase with time.Several healthcare offices still use antiquated frameworks for maintaining patient records.These frameworks are beneficial for keeping patient information records close at hand.This might make it difficult for the professional to analyze, which can be tiresome for both the specialist and the patients.As a result, the cost of maintaining a patient-centered business increases substantially [41,42].The majority of the present healthcare data infrastructure relies on reputable third parties.In numerous instances, however, they cannot be relied upon.A potential answer to this issue is the blockchain, which depends on consensus and does not need a central authority.

Methodology
This study continues by defining the used approach.The systematic study is confined to the subject of medical data sharing.

Research Questions
The purpose of the study was to address the following research questions (RQs): RQ3: What are the issues of using blockchain to share medical data?

Databases
Included in the systematic review were the following databases: Using the query string(s) listed below, a search for related articles was conducted.Based on the study domain and the established RQs, the search strings were developed.These keywords have been used in the search: The online digital library search was performed on 14 March 2023.The search query was purposely designed to be as comprehensive as feasible to evaluate as many results as possible that were relevant to the research topics given in this systematic review.By searching in the title of the articles, 284 total items were discovered via the main search.The online digital library search was performed on 14 March 2023.The search query was purposely designed to be as comprehensive as feasible to evaluate as many results as possible that were relevant to the research topics given in this systematic review.By searching in the title of the articles, 284 total items were discovered via the main search.Figure 2 shows a summary of the search and selection technique used to choose the articles.

Selection of Studies
Depending on the criteria, articles were either included or excluded from the systematic review (Table 2).Fifty papers were ultimately included in the systematic review.To ensure that only high-quality and relevant research was examined, the approach was rigorous.

Selection of Studies
Depending on the criteria, articles were either included or excluded from the systematic review (Table 2).Fifty papers were ultimately included in the systematic review.To ensure that only high-quality and relevant research was examined, the approach was rigorous.

Limitations
One issue is due to the scope of attention; as systematic reviews have a confined focus.Another restriction concerns the study selection, information loss on critical outcomes, incorrect subgroup analysis, and inconsistency with the unique experimental results [43].
Limited databases and the title search query are other limitations of this review.The decision to use only article titles as the search query for this systematic review was motivated by the need to conduct a preliminary investigation of the topic within the limitations of time and resources.This method has several limitations, including the possibility of omitting relevant studies, a reduced precision in the study selection, and the risk of bias.

Discussion
RQ1: How established is blockchain in medical data sharing, and how has this evolved?This systematic review looked for articles published between 2017 and 2022 on the use of blockchain technology in the exchange of medical data.Figure 3   4. System design must not be defined properly

Limitations
One issue is due to the scope of attention; as systematic reviews have a confined focus.Another restriction concerns the study selection, information loss on critical outcomes, incorrect subgroup analysis, and inconsistency with the unique experimental results [43].Limited databases and the title search query are other limitations of this review.The decision to use only article titles as the search query for this systematic review was motivated by the need to conduct a preliminary investigation of the topic within the limitations of time and resources.This method has several limitations, including the possibility of omitting relevant studies, a reduced precision in the study selection, and the risk of bias.

Discussion
RQ1: How established is blockchain in medical data sharing, and how has this evolved?This systematic review looked for articles published between 2017 and 2022 on the use of blockchain technology in the exchange of medical data.Figure 3 provides a bibliometric summary of the selected articles.Only two articles were published over the years 2017 and 2018.In 2019, four papers were published.The years 2020 and 2021 each have nine items.With 24 papers published in 2022, the growth rate has risen.It contains 48 percent of all papers in this review.This demonstrates that blockchain research in medical data sharing is very important, and expanding, and shows no indication of slowing down.Blockchain enables enterprises to offer proper patient care and provide access to highquality healthcare services.With this technology, health information exchange, a substantial strain owing to its repetitive nature and time-consuming nature, is swiftly alleviated.Adoption and implementation of blockchain in healthcare systems and organizations for the sharing of medical data should be thoroughly evaluated.Various factors, including regulatory frameworks, technological challenges, interoperability, data protection, and stakeholder acceptance, need to be considered.Several research and development initiatives are investigating the potential of blockchain for medical data sharing, as its popularity and importance have risen dramatically.Initially, research concentrated on the theoretical foundations and viability of blockchain in this domain, resulting in the development of frameworks, methods, and protocols tailored to address the unique challenges of medical data sharing.As the technology advanced, efforts were made to improve the effectiveness and functionality of blockchain in the sharing of medical data, including refining data storage and retrieval, optimizing consensus processes, and exploring integration with other cutting-edge technologies such as edge computing and IoT.
Despite growing interest and research in this area, blockchain technology for the sharing of medical data is still in its infancy.Numerous proposed solutions are still in the experimental or proof-of-concept stages and require additional validation, standardization, and integration with the current healthcare infrastructure.To accomplish a widespread blockchain adoption in the healthcare industry, adoption, regulation, interoperability, and scalability issues need to be resolved.These developments are required to ensure the successful deployment of blockchain technology for the secure and efficient exchange of medical data, which will benefit healthcare stakeholders and facilitate the improvement of healthcare outcomes.
RQ2: What are the latest developments in blockchain-based medical data-sharing research?There are several instances in which blockchain is utilized to share medical data.Rajput et al. [44] propose a system for healthcare management that leverages blockchain technology to create a tamper-protection application by taking into account secure rules.In an emergency case, these regulations specify extendable access control, auditing, and tamper resistance.Hu et al. [45] propose CrowdMed-II, a blockchain-based health data management architecture that might solve the aforementioned issues with health data.In their framework, they investigate the architecture of significant smart contracts and suggest two smart contract structures.In addition, a unique search contract for searching patients is introduced.They assess their efficacy based on Ethereum's execution costs.The paper by Hashim et al. [46] presents a transaction-based smart contract-triggering method for inter-blockchain communication, allowing the exchange of electronic health records (EHRs) across separate blockchains.They employ local and global smart contracts that will be executed whenever a blockchain-based transaction is generated.Local smart contracts are used to share EHRs inside a blockchain, while global smart contracts are used to share EHRs across blockchains that are independent of one another.Using the Hyperledger Fabric blockchain technology, the experimental setup is executed.In a health federation arrangement, inter-blockchain communication between two separate fabric networks is handled by a global smart contract using Hyperledger Cactus for EHR exchange.
Wu et al. [47] build a blockchain-enabled framework for dynamic access control coupled with local differential privacy (LDP) techniques to offer attribute-based privacy protection in transaction processing.In the framework, they develop four kinds of smart contracts to suit the needs of anonymous transactions, dynamic access control, advantageous matching decisions, and the assessment of disclosed data.To provide granular privacy protection, they categorize critical EMR parameters into distinct tiers and randomize them before data publication using differential privacy budgets.In addition, they create a data quality function that illustrates the disruption caused by LDP-based privacy preferences from the requester's perspective, and they propose suitable many-to-many matching selections among participants for advantageous transactions.Specifically in the study by Kumar et al. [48], deep learning and permissioned blockchain uses a blockchain system to register, verify (using zero-knowledge evidence), and validate communicating entities by utilizing a consensus process based on smart contracts.The authenticated data are then utilized to propose a unique DL strategy that combines a stacked sparse variational autoencoder (SSVAE) with self-attention-based bidirectional long short-term memory (SA-BiLSTM).In this system, SSVAE encodes or converts healthcare data to a new format, while SA-BiLSTM detects and enhances the attack detection process.
Several blockchain implementations, encryption strategies, and IoT-based systems are the three main categories of current system platforms for exchanging medical data.Table 3 outlines research proposing blockchain solutions for exchanging medical data.

Types of Blockchain
There are four primary forms of blockchain networks, including public blockchains, private blockchains, consortium blockchains, and hybrid blockchains.Each of these systems has advantages, disadvantages, and optimal applications.The paper by Zhang and Lin [49] offers a blockchain-based safe and privacy-preserving protected health information (PHI) sharing (BSPP) protocol for enhancing e-health system diagnostics.Initially, the data architecture and consensus procedures for the two types of blockchains-private blockchain and consortium blockchain-need to be designed.The private blockchain is responsible for storing PHI, while the consortium blockchain maintains the PHI's safe indexes.To ensure privacy preservation, access control, data security, and secure search, all data, including PHI, keywords, and patient identities, are encrypted with a public key using keyword search.Two kinds of blockchains, private and consortium blockchains, are developed in another research by Shamshad et al. [50] by defining their consensus, data formats, and procedures.A private blockchain is responsible for the maintenance of EHRs, while a consortium blockchain keeps the safe indexes of EHRs.To achieve data security, secure search, access management, and the protection of patient privacy, all EHRs are public-key encrypted with an appropriate search phrase.

Encryption
Encryption of medical data facilitates electronic data transmission and the sharing of clinical patient data and documentation.Regardless of location, patient medical data may be exchanged within a health system or transmitted to permitted health systems.In the study by Yang et al. [51], first, the encrypted medical data are saved in the cloud, and then the storage address and medical-related information are entered into the blockchain, thus ensuring efficient storage and eliminating the risk of irreversible data change.The proposed approach combines attribute-based encryption (ABE) and attribute-based signature (ABS) to enable the exchange of medical data in many-to-many interactions.The ABE provides data privacy and fine-grained access control, while the ABS confirms the source of medical data while safeguarding the signer's identity.In addition, the majority of medical data ciphertext decryption activities are outsourced by the data user to the cloud service provider (CSP), which may significantly minimize the computing strain.In a separate investigation, Sun et al. [52] conduct a hash computation on the EMR and record the resulting value on the blockchain to assure the data's integrity and validity.They encrypt the EMR and put it in the distributed storage protocol interplanetary file system.The encrypted keyword index information of EMRs was saved on Ethereum, and instead of relying on a centralized third party, a smart contract implemented on Ethereum was utilized to perform keyword searches.In addition, they use the ABE method to guarantee that only the access policycompliant qualities may decode the encrypted EMR.Zhang et al. [53] address these issues by providing a distributed PHR-sharing mechanism based on blockchain and ciphertext policy ABE (CP-ABE), which enables efficient encryption and decryption.In addition to maintaining the data's integrity and tracking its source, blockchain records all activities on the data as transactions.In addition, the nodes of the blockchain serve as attribute authority for the CP-ABE cryptosystem.Tracing cryptographic techniques enables the identification of rogue blockchain nodes.Furthermore, the recovery of ciphertext is made fair via the use of smart contracts.To circumvent the restricted storage capacity of blockchain, our innovative solution employs both on-chain and off-chain storage options.
In the study by Zhang et al. [54], the deniably authenticated searchable encryption scheme (DASES) utilizes blockchain to assure the integrity, immutability, and traceability of image data, while circumventing the blockchain's storage and processing limitations.Not only can the DASES survive an inside keyword guessing attack (IKGA), but it can also offer good privacy protection and validate the validity of medical picture data.Secondly, they demonstrate that the DASES meets the ciphertext and trapdoor indistinguishability conditions.Regrettably, the DASES is less efficient than other comparable systems in the literature, but its largest asset is its capacity to provide an improved identity privacy protection and enhanced security.The application created by Cheng et al. [55] enables the physician to access the patient's personal history EMRs with the patient's permission to comprehend the patient's sickness history and build a new medical record for the patient.The server calculates the ciphertext and adds it to the patient's medical record to complete the case update.Via hierarchically storing patient information, medical staff information, and medical records, Yuan et al. [56] devise a three-chain paradigm.The combination of interplanetary file system (IPFS) technology and the encryption algorithm guarantees the security and efficiency of data storage off-chain.Attributes are used to classify users, and ABE technology is used for the secondary encryption of the key and ciphertext channel.However, hierarchical encryption drastically reduces the chance of a system assault.Zhang et al. [57] provide a unique blockchain-based data sharing system (BDSS) with fine-grained access control and permission revocation for the medical context.With this concept, they divide the EMR into public and private sections.Next, they employ symmetric searchable encryption (SSE) technology to encrypt these two pieces independently, and ABE technology to encrypt the symmetric keys used by SSE technology.Based on CP-ABE, Tan et al.
[58] present a blockchain-enabled security and privacy protection system for COVID-19 medical records with traceable and direct revocation.With this system, all public keys, revocation lists, etc., are maintained on a blockchain, and the blockchain is used for consistent identity authentication.The system management server is responsible for producing the system settings and publishing the COVID-19 medical practitioners' and users' private keys.Using policy matching, the cloud server provider (CSP) maintains the CEMRs and creates the intermediate decryption parameters.If the user has private keys and intermediate decrypt parameters, he or she may compute the decryption key.Chen et al. [59] offer BFHS, a blockchain-based method for the safe, granular exchange of EHRs.On BFHS, they encrypt EHRs using ciphertext-policy ABE and upload them to the IPFS for storage, whilst the matching index is encrypted with proxy re-encryption and stored on a medical consortium blockchain.In addition, a credit evaluation system was developed and included in the smart contract.The combination of smart contracts, proxy re-encryption, a credit assessment system, and IPFS provides patients with a secure EHR sharing environment and a dynamic access control interface.

Ciphertext
Ciphertext is the result of an encryption algorithm transforming plaintext into encrypted text.Ciphertext cannot be read until it has been decrypted (converted to plaintext) using a key.Decryption cipher is a method that converts ciphertext to plaintext.Yang et al. [60] propose a novel blockchain-based keyword search protocol with dual authorization for the exchange of EHRs.The certificateless cryptosystem eliminates key escrow and certificate administration.The development of the authorization matrix enables the dual authorization of user identities and searchable departments.Moreover, the matrix may manage user access privileges.The ciphertext index signal value enables an authoritative control over the ciphertext index.The ciphertext MAC verification code kept on the blockchain can check for the legality of ciphertext, and smart contracts are utilized to guarantee fair transactions.Yang et al. [61] encrypt keywords using the certificateless cryptosystem, which eliminates the certificate administration and key escrow issues.The suggested approach also enables multi-user searches, and the user authorization table may be utilized to adjust medical data users' access rights.In addition, the root values of the Merkle trees are recorded in the blockchain to assure the search results' immutability, integrity, and traceability.In addition, a smart contract facilitates a fair transaction between a cloud service provider and customers of medical data without the need for trusted third parties.They demonstrate that the suggested technique is safe against the random oracle model's keyword-guessing attack.Lai et al. [62] propose a secure medical data-sharing system based on a traceable ring signature and blockchain as a solution to the issue of medical institutions' challenges in exchanging medical data.First, a certificateless traceable ring signature mechanism based on distributed key generation is suggested to preserve data integrity and privacy.The combination of a smart contract with access control and a self-controlling object (SCO) enables the outsourcing of decryption and the sharing of data.In addition, the suggested approach leverages the IPFS to store the seas of medical privacy data and encrypts the hash index to store it, which increases data sharing efficiency.Using the consensus process, they may choose the proxy node and upload the SCO package to the blockchain node for data exchange after the blockchain has been incorporated.

IoT-Based Systems
With healthcare mobility solutions, IoT may automate the workflow of patient care by automating the workflow of patient care.Data transfer, machine-to-machine connectivity, and interoperability have increased the productivity of healthcare sectors.Healthcare professionals and patients may save time with IoT integration.Chen et al. [63] presented a health IoT-based blockchain data-sharing system that protects privacy.To allow patients to construct granular privacy protection, they devised a privacy-preserving mechanism based on the content extraction signature system.They created a Byzantine fault-tolerant leader election method that improves the Raft algorithm's security and data-sharing efficiency.In addition, they built a summary contract to facilitate the retrieval of data.Pang et al. [64] propose a patient-controlled EHR-sharing system based on blockchain technology and cloud computing.To prevent tampering, the medical abstract and access strategy are kept on the blockchain.To accomplish fine-grained access control, they suggest encrypting EHRs using ABE and multi-keyword encryption.In addition, they suggested a node-statecheckable practical Byzantine fault tolerance consensus method to prevent Byzantine nodes from gaining access to the consortium blockchain.Nie et al. [65] present a new blockchainbased safe-sharing system with searchable encryption and a concealed data structure through IoT devices.Data owners' EHR ciphertexts are kept in the interplanetary file system (IPFS).A user with the appropriate access rights may search for the needed data using the data owner's time-limited authorization and validate the search result's legitimacy.With a symmetric key, the data user may then obtain the appropriate EHR ciphertext from IPFS.In IoT applications, the technique combines searchable encryption and smart contracts to provide safe search, time management, verified keyword search, quick search, and forward privacy.Wang et al. [66] present a consortium-based blockchain-based PHR management and sharing system that is both security-conscious and privacy-preserving.The PHR ciphertext of Internet of medical things (IoMT) is stored using the interplanetary file system (IPFS).Hence, zero-knowledge proof may be used to validate keyword index authentication on the blockchain.In addition, the system combines modified attribute-based cryptographic primitives with custom-tailored smart contracts to offer safe search, privacy preservation, and individualized access control in IoMT situations.Wu et al. [67] present a triple-subject purpose-based access control (TS-PBAC) model that is compatible with a blockchainenabled reliable transaction network, and they design an individual-centric security and privacy-preserving mechanism for access control with varying purposes and roles in IoMT scenarios.Particularly, they develop a hierarchical purpose tree (HPT) and associated regulations to ensure the legality of an external user who has several purposes.They create a LDP-based policy and role-based access control mechanism in an edge computing paradigm to award fine-grained permissions to authorized users to increase the privacy of sensitive characteristics against an internal attacker.

Blockchain Role Year Capability Smart Contract Reference
Trust-less medical data sharing 2017 Access control mechanism [68] Blockchain-based data sharing for electronic medical records 2017 Receive data from the shared pool once identities and cryptographic keys have been validated [69] Efficient and secure medical data sharing 2018 The enhanced consensus technique delivers EMR consensus without significant network congestion or energy consumption [70] Secure and privacy-preserving data sharing 2019 Session-based flexible healthcare data sharing [71] Table 3. Cont.

Blockchain Role Year Capability Smart Contract Reference
Blockchain-based searchable encryption 2019 Complete control over data access [72] Efficient healthcare data sharing 2019 Mutual authentication and the generation of a session key [73] Privacy-preserving data sharing 2019 Fine-grained access control, keyword search, and privacy protection [74] Secure and privacy-preserving data sharing 2020 Using bilinear mapping and intractable issues, the authentication process's security danger may be neutralized. [75] Efficient and secure data sharing 2020 Verification by zero-knowledge proof, decryption using proxy re-encryption technology, and PBFT-based distributed consensus [76] Privacy-preserving data sharing 2020 The data usage ontology and the automatable discovery and access matrix comprise the dynamic consent model [77] Fine-grained access control and privacy protection 2020 In the random oracle paradigm, keyword indistinguishability against adaptively selected keyword assaults [78] Protected data sharing 2020 Couples with privacy-sensitive information are stored on the consortium blockchain, while non-sensitive data are shared on the public blockchain [79] Privacy-preserving medical data sharing 2021 Scheme for anonymously transmitting medical data based on proxy re-encryption algorithm and cloud servers [80] Secure data sharing 2021 Proxy re-encryption protocols [81] Protected data sharing 2021 Searchable encryption and K-anonymity [82] Consortium-based data sharing 2021 Allowing data requesters to comply with data access requirements and to build their standing within a consortium [83] Secure and privacy-preserving data sharing 2021 The outsourced business has no access to the server or its data [84] Secure and distributed data sharing 2021 Data ownership, data traceability, data consistency, privacy protection, data security, and distributed storage [85] Secure data storage and sharing 2021 Certificateless public key cryptography and elliptic curve cryptography (ECC) [86] Hierarchical data sharing with access control 2022 Fine-grained access control, efficient retrieval across encrypted PHRs with low-consumed hierarchical key distribution and key leakage resistance, as well as efficient aggregative authentication [87] Searchable encryption with access control 2022 Algorithm for key-policy ABE [88] Privacy-preserving data sharing 2022 The condition is concealed inside the re-encryption key so that the proxy cannot discover it [89] Table 3. Cont.

Blockchain Role Year Capability Smart Contract Reference
Protected and integrated data sharing 2022 Storing encrypted medical data in dispersed storage mode and integrating patient data across offline institutions and platforms [90] Privacy-enhanced data storage and exchange 2022 Patients' personal information is held on off-chain storage (IPFS), while other information is saved on the blockchain ledger, which is available to all participants [91] Hybrid storage with access control 2022 Feasibility of recovery of the encryption keys [92] Secure data sharing with access control 2022 Immutability, fine-grained access control, and traceability [93] In the sphere of blockchain-based medical data sharing, there are common concepts and tendencies.These papers highlight the use of blockchain technology to facilitate the secure and trustless sharing of medical data, addressing issues of trust, security, and privacy.These solutions seek to provide a tamper-resistant and transparent infrastructure for storing and sharing sensitive medical information by leveraging the distributed and decentralized nature of blockchain in conjunction with cryptographic techniques.
In these blockchain-based systems, privacy and data security are top priorities.Several methods, including encryption techniques, access control mechanisms, and privacypreserving algorithms, are used to protect the privacy of patient information while allowing authorized parties to access relevant data.In addition, attribute-based access control and fine-grained access control mechanisms are frequently employed, enabling data owners to define access policies based on particular attributes or duties.Frequently, consortium or permissioned blockchains are utilized, allowing multiple trusted parties to collaborate and administer the shared data.Moreover, interoperability, consent management, and compliance with regulations such as the General Data Protection Regulation (GDPR) are also essential considerations for these solutions.These trends highlight the growing interest in utilizing blockchain technology to establish secure, privacy-preserving, and interoperable medical data-sharing systems.
Various research studies are garnering interest in the application of blockchain technology to the exchange of medical data.Several approaches and frameworks have been proposed by researchers to resolve the challenges associated with health data exchange.These methods make use of blockchain characteristics such as tamper resistance, secure rules, extendable access control, auditing, and counterfeit protection.They investigate the architecture of smart contracts, devise methods for inter-blockchain communication, and assess the efficacy of these systems by calculating execution costs.Integrating encryption methods such as attribute-based encryption (ABE) and ciphertext-policy ABE (CP-ABE) with blockchain ensures privacy protection, granular access control, and secure search.Consideration is given to public, private, consortium, and hybrid blockchains for the secure storage and management of medical data.Moreover, techniques such as hash computation, deniably authenticated searchable encryption schemes (DASES), and smart contracts are utilized to guarantee data integrity, validity, and traceability.By integrating blockchain technology with encryption techniques, researchers hope to develop dependable systems that improve data security, privacy, and the exchange of medical information.
RQ3: What are the issues of using blockchain to share medical data?Using blockchain technology for sharing medical data presents several issues that need to be addressed.Firstly, scalability is a major concern.Blockchain networks may struggle to manage the large volumes of data involved in sharing EMRs among multiple stakeholders.Scaling the blockchain to accommodate these demands is essential for efficient data sharing [69].Ensuring the privacy and confidentiality of sensitive medical data is paramount in healthcare systems.While blockchain offers immutability and transparency, it presents challenges in protecting patient privacy and maintaining data confidentiality.Innovative solutions must be developed to address these concerns and provide robust privacy measures in blockchain-based medical data-sharing systems [70].
Another significant issue is the performance and efficiency of blockchain networks.Public blockchains, in particular, can experience slow transaction-processing speeds and high energy consumption.These limitations hinder the real-time access and responsiveness required for sharing medical data effectively.Optimizing blockchain performance and energy efficiency is crucial to ensure seamless data sharing [74].Additionally, the interoperability of blockchain with the existing healthcare infrastructure is a challenge.Integrating blockchain into diverse systems and ensuring compatibility with legacy systems is complex.Achieving seamless interoperability among different healthcare providers and systems is crucial for effective medical data sharing.Addressing this issue requires careful planning and implementation strategies [75].
Regulatory and legal considerations play a significant role in blockchain-based medical data sharing.Compliance with data protection laws, such as GDPR, is necessary.However, the decentralized nature and immutability of blockchain can make it difficult to meet certain regulatory obligations, such as data deletion and consent management.Developing frameworks that align with regulatory requirements is vital to ensure compliance while leveraging the benefits of blockchain technology [91].Lastly, establishing a governance framework and building trust among participating entities are critical aspects of blockchainbased medical data sharing.The distributed nature of blockchain requires robust consensus mechanisms and trust models to guarantee data integrity and reliability.Creating effective governance structures that address the needs and concerns of all stakeholders is essential for successful implementation [81].
The use of blockchain for sharing medical data poses several challenges.Scalability, privacy and confidentiality, performance and efficiency, interoperability, regulatory compliance, and governance and trust are among the key issues that need to be addressed.Overcoming these challenges is crucial for the successful implementation of blockchainbased solutions in healthcare, enabling secure, efficient, and privacy-preserving sharing of medical data.Table 4 provides an overview of the various research papers pertaining to blockchain-based medical data-sharing schemes.Using blockchain technology for sharing medical data presents several technical challenges that need to be addressed for successful implementation in healthcare systems.Scalability is a major concern due to the large volumes of data involved, requiring the blockchain networks to be scaled appropriately.The privacy and confidentiality of sensitive medical data need to be ensured, necessitating the development of innovative solutions such as attribute-based encryption and robust access control policies.Performance and efficiency issues, including slow transaction-processing speeds and high energy consumption, need to be optimized for real-time data access.Interoperability with existing healthcare infrastructure requires careful integration and compatibility planning.Regulatory compliance, particularly with data protection laws like GDPR, is crucial, and frameworks aligning with these requirements need to be developed.Establishing a governance framework and building trust among participants is essential, necessitating robust consensus mechanisms and effective governance structures.Overcoming these challenges will enable the secure, efficient, and privacy-preserving sharing of medical data, leading to improved healthcare outcomes.

Conclusions
As medical technology progresses, there is a rising demand for healthcare professionals throughout the globe to communicate an expanding number of data safely.Blockchain is commonly used in the healthcare industry to provide a comprehensive knowledge of patient information and monitor data-sharing permission.It is a robust technology that enables numerous parties to view and exchange data securely.Considering the huge difficulty that healthcare organizations confront in digitizing and exchanging health information, it is not surprising that many are striving to enhance healthcare operations via the use of blockchain.Using publications published between 2017 and 2022, this review examines the present status, research trends, and problems of blockchain in medical data exchange to address the existing gap.
To attain this purpose, RQs were formulated and a predetermined technique was used to reduce the number of articles reviewed to 50.They were then studied further.Our results show that blockchain technology development and its use in the exchange of medical data are growing.Hence, most of blockchain's potential remain untapped.Most of the studies propose a unique framework, architecture, or methodology for medical data exchange by utilizing blockchain technology.As there are a multitude of benefits in exchanging patient data in a safe, decentralized manner, it is difficult to comprehend why the industry has not determined and concluded on using this concept earlier.Nevertheless, as with many factors in the commercial sector, there are actual reasons as to why it is difficult to exchange healthcare data.It seems that countless challenges must be addressed before blockchain can become the dominant industrial technology.

Figure 1 .
Figure 1.Blockchain in a smart contract process.

Figure 1 .
Figure 1.Blockchain in a smart contract process.

Figure 2
shows a summary of the search and selection technique used to choose the articles.AND Health record sharing.

Figure 2 .
Figure 2. Process of study selection.

Figure 2 .
Figure 2. Process of study selection.
provides a bibliometric summary of the selected articles.Only two articles were published over the years 2017 and 2018.In 2019, four papers were published.The years 2020 and 2021 each have nine items.With 24 papers published in 2022, the growth rate has risen.It contains 48 percent of all papers in this review.This demonstrates that blockchain research in medical data sharing is very important, and expanding, and shows no indication of slowing down.Blockchain enables enterprises to offer proper patient care and provide access to high-quality healthcare services.With this technology, health information exchange, a substantial strain owing to its repetitive nature and time-consuming nature, is swiftly alleviated. objectives

Figure 3 .Figure 3 .
Figure 3.The trend of publishing articles between 2017 and 2022.Adoption and implementation of blockchain in healthcare systems and organizations for the sharing of medical data should be thoroughly evaluated.Various factors, including regulatory frameworks, technological challenges, interoperability, data protection, and stakeholder acceptance, need to be considered.Several research and development

Table 1
displays the highlights of blockchain-enabled smart contracts.

Table 2 .
Standards of inclusion and exclusion.

Table 2 .
Standards of inclusion and exclusion.
4. Article should contain and clearly outline research objectives 4. System design must not be defined properly

Table 3 .
Summary of studies that propose blockchain systems in medical data sharing.

Table 4 .
Challenges and possible solutions of blockchain-based medical data-sharing schemes.