key: cord-0768227-4zx7ralg
authors: Mahajan, Hemant B.; Rashid, Ameer Sardar; Junnarkar, Aparna A.; Uke, Nilesh; Deshpande, Sarita D.; Futane, Pravin R.; Alkhayyat, Ahmed; Alhayani, Bilal
title: Integration of Healthcare 4.0 and blockchain into secure cloud-based electronic health records systems
date: 2022-02-04
journal: Appl Nanosci
DOI: 10.1007/s13204-021-02164-0
sha: afcda1d7dbecef5c8f0b1c81599e79c5329dc5dd
doc_id: 768227
cord_uid: 4zx7ralg

Since the last decade, cloud-based electronic health records (EHRs) have gained significant attention to enable remote patient monitoring. The recent development of Healthcare 4.0 using the Internet of Things (IoT) components and cloud computing to access medical operations remotely has gained the researcher's attention from a smart city perspective. Healthcare 4.0 mainly consisted of periodic medical data sensing, aggregation, data transmission, data sharing, and data storage. The sensitive and personal data of patients lead to several challenges while protecting it from hackers. Therefore storing, accessing, and sharing the patient medical information on the cloud needs security attention that data should not be compromised by the authorized user's components of E-healthcare systems. To achieve secure medical data storage, sharing, and accessing in cloud service provider, several cryptography algorithms are designed so far. However, such conventional solutions failed to achieve the trade-off between the requirements of EHR security solutions such as computational efficiency, service side verification, user side verifications, without the trusted third party, and strong security. Blockchain-based security solutions gained significant attention in the recent past due to the ability to provide strong security for data storage and sharing with the minimum computation efforts. The blockchain made focused on bitcoin technology among the researchers. Utilizing the blockchain which secure healthcare records management has been of recent interest. This paper presents the systematic study of modern blockchain-based solutions for securing medical data with or without cloud computing. We implement and evaluate the different methods using blockchain in this paper. According to the research studies, the research gaps, challenges, and future roadmap are the outcomes of this paper that boost emerging Healthcare 4.0 technology.

Healthcare 4.0 is a phrase that has developed lately and received from Industry 4.0. Nowadays, the healthcare area is more digital than earlier days; for instance, growing from magnetic resonance imaging (MRI) and X-rays to computed tomography (CT) and ultrasound scans to electronic medical documents. Medical data processing is an important task of the Healthcare 4.0 standard. Since from the last decade, it observed that healthcare is dataintensive technology in which a huge amount of data introduced, disseminated, saved, and fetched frequently. When the patient undergoes any tests, for example, its data are created that further needs to disseminate to the medical experts like radiographer and physician. In smart healthcare systems, the medical data stored in the hospital servers by considering the future requirements of accessing by the authorized physician from the hospital located within their networks. A significant role can play by technology while improving the quality of service for the patients. It allows data analytics to take appropriate medical decisions. Additionally, it helps to reduce the costs by the efficient allocation of medical resources such as equipment, personnel. (Taichman et al. 2016; Chen et al. 2014) . It noticed that the data written in the paper form is difficult to fetch in digital form as it needs the extra manpower, costly to archive, and also leads the data entry errors. Such challenges may lead the failure in medical decisions due to lack of complete/accurate medical information and hence may require the repeated tests of patients. It increases the unnecessarily increasing costs expenses and patients inconvenience (Raghupathi and Raghupathi 2014; Krumholz and Waldstreicher 2016) .

Hence medical data dissemination has received the researcher's attention for novel approaches for patient treatment. The digitization, electronic storage, and medical data remote access by the medical experts are a key base for an above-said statement (Costa 2014) . The electronic information about the patients created by the hospitals since after their visit and making them individual owners of such electronic data (Huang et al. 2014) . With the appearance of that technology era and the succeeding acquisition of large amounts of data that have received in the big data age, sharing data gives interesting value on views that are still opening. The significance of medical data and the integration with its distribution has given origin to enterprise substances that consolidate, process, interpret, store, and presented the appropriate incentive distribution of data with other connected individuals (Huang et al. 2018; Aceto et al. 2013; Assis et al. 2014; O'Driscoll et al. 2013) . It has gained the attention of several enterprises with a center on cloud storage and processing tools, data analytics, and data derivation rendering established enterprises province on data accessible on their progress and durability. The Cloud Service Providers (CSPs) were introduced to deliver cross-domain, flexible, and controlled medical data sharing as well as data searching functions for the end-users (Borgman 2011) .

Due to the industrial nature, assuring the integrity, security, privacy of medical data is essential. Thus it required the efficient and secure framework of data management (Grozev and Buyya 2012) . The CSP contested with a necessity of collaboration for medical data sharing because of unfavorable hazards acted on exhibiting the details on their data (Fazio et al. 2015) . For data masters and managers, it is the actual danger of received data revealed in the controls of attacker data users (Kuo 2011; Weber et al. 2014; Shao et al. 2015) . To address such challenges many cryptographic techniques have been introduced for secure healthcare data storage and sharing, however, they have still been inadequate (Thilakanathan et al. 2014; Khan et al. 2014; Dong et al. 2014; Yang et al. 2015) . The cryptography techniques are proposed by considering the cloud server's untrustworthiness and the user's data privacy. It's important to perform data encryption before outsourcing it to the cloud server. But the direct use of conventional encryption methods withholds users of search capability and thus ends in poor user experience. To secure the data search over the encrypted medicinal data, searchable encryption methods have been produced in two characteristic settings including the symmetric-key setting and the public-key setting. The symmetric-key has an effective way compared to the public-key setting, but the number of difficulties that have not been addressed effectively for keyword searches over the encrypted medical data either by the patient or medical experts. The main challenges that threats the medical data security are user side verification (patient should be valid user), server-side verification, without the need of a trusted third party to store, retrieve, and search the medical information efficiently.

Recent studies have demonstrated that blockchain is a solid fit to give a reasonable answer to such issues based on its appealing highlights like immutability and decentralization. The blockchain methodology has proven an effective solution to achieve higher security and computation efficiency compared to the conventional cryptography solutions for cloud data processing. The recent works introduced the blockchain for secure data processing (Tschorsch and Scheuermann 2016; Azaria et al. 2016; Zhang et al. 2016) . The blockchain is a technology ready to assemble an open and circulated online database comprises a rundown of data structures called obstructs that are connected to fabricate the chain. These blocks are conveyed among numerous hubs of a foundation and not halfway put away. Each block contains a timestamp of its production, the hash of the past block and the exchange data, a patient's healthcare data, and the healthcare supplier data. In this paper, our point is to study the various solutions of blockchain-based security for medical data storage and sharing in the cloud domain to notice the current research gaps, challenges, and future roadmap that help to design Healthcare 4.0. Section 2 presents the Healthcare 4.0 components. The architecture of blockchain methodology for data security presented. Section 3 presents a systematic review of blockchain-based security solutions. Section 4 presents the research gaps, challenges of current solutions, and future roadmap. Section V presents the conclusion and future work.

For healthcare 4.0, several components considered to establish the remote health monitoring and emergency control. This section presents the design of cloud-based healthcare data processing, security requirements, and emergence of blockhain technology.

In general, Electronic Medical Records (EMRs) contain therapeutic and clinical data identified with a given patient and put away by the dependable healthcare supplier. It encourages the recovery and examination of healthcare data. To more readily bolster the administration of EMRs, early ages of Healthcare Information System (HIS) planned with the ability to make new EMR examples, store them, and question and recover put away EMRs of interest. HIS can be moderately straightforward solutions and schematically depicted as a graphical user interface or a web administration. These are commonly the front-end with a database at the back-end, in concentrated or disseminated implementation. With patient portability (both inside and remotely to a given nation) being progressively the standard in the present society, it wound up evident that numerous independent EMR solutions must make interoperable to encourage the sharing of healthcare data among various suppliers. Even crosswise over national fringes, as required.

To encourage data distribution and patient data dispatch capability, there is a demand for EMRs to formalize their data composition and the design of HIS. The EHRs are designed to facilitate patient therapeutic records to proceed with the victim or be made available to diverse healthcare suppliers. EHRs have an improvident data structure compared to EMRs. There are supplementary actions to develop up HIS and foundations to balance and sustain future demands, as approved by the various national and global enterprises. For example, the Fascicolo Sanitario Elettronico (FSE) venture in Italy, the epSOS venture in Europe, and a continuous task to institutionalize the sharing of EHRs. As of late, the inescapability of savvy devices (Android and iOS devices and wearable devices) has likewise brought about a change in perspective inside the healthcare business. Such devices can be client possessed or introduced by the healthcare supplier to gauge the prosperity of the clients (for example, patients) and educate/encourage treatment and observing of patients. For instance, there is a wide scope of portable (applications) in wellbeing, wellness, weight reduction, and other healthcare-related classes. These applications predominantly work as the following apparatus, for example, enlisting client exercises/exercises, keeping the check of devoured calories, and different insights (for example, number of steps taken, etc.

There are likewise devices with implanted sensors for further developed therapeutic errands, for example, bracelets to quantify heartbeat during exercises, or devices for self-testing of glucose. The data (for example, the client's crucial signs) can be consistently accumulated and sent progressively to a brilliant gadget, before being sent to a remote healthcare cloud for further analysis. The ongoing improvements made ready for Personal Health Records (PHR), where patients progressively engaged with their data collection, observing their wellbeing conditions, and so on, utilizing their advanced mobile phones or wearable devices (for example, shrewd shirts and brilliant socks). With such systems, several challenges associated such as related to the process of medical data collection and its processing:

• Should we depend on medical data gathered by end-users themselves? • Should the appropriate healthcare providers approved data gathered by the subjects, and if consequently, whence can that be achieved? • Who should be professionally responsible for misdiagnosis or late diagnosis, because of judgments being made on the data transmitted from the device of the patient that is afterward confirmed to be inaccurate or flawed?

Despite the above-listed challenges of healthcare systems, the presence of such a system can provide seamless data sharing among hospitals, and patients who provide the abstraction of single wellbeing data stockpiling for some random patient will profit all clients, going from patients to social insurance suppliers to governments. The well-known framework called cloud computing is an appropriate solution as it supports the real-time data sharing all over the world, supports resource elasticity, and handling the big data to fetch the important information from the enormous medicinal services data for research and strategy basic leadership. General cloud-based system of storing and sharing the medical data among the different providers which supporting every supplier in dealing with their data, giving a consistent method for trading and possibly ensuring data among EHR and PHR, and giving a bound together perspective on human services records for every patient. As showing in Fig. 1 , all key terms of healthcare systems demonstrated such as PHR in which the patients collect their data and store in the cloud, EMR at every healthcare provider which can access the reports of the individual patient from the cloud storage, and EHR, a cloud storage system from which the user or hospitals can access the medical history of the patient when it's required from any geographical location.

As the medical reports containing the sensitive data of individuals, it may get attention from hackers. The attackers looking to profit monetarily from the hacking of individual medicinal data as it would hold any importance with specific associations or industries. Thus it becomes essential to provide security for systems like EHR, PHR, and EMR. Moreover, the privacy and integrity of healthcare attacks can be purposeful and unintentional, and associations might be punished or held criminally obligated for such episodes, for instance, under the Medical coverage Compactness and Accountability Act. Since from the last two decades, how to secure such a system that ensures the protection and integrity of the data is increasingly critical considerations. Strategies incorporate utilizing cryptographic natives, for example, those dependent on an open key foundation and open mists to guarantee data secrecy and protection (Nepal et al. 2015) . But such methods having the limitation of data searching as in medicinal services suppliers need to unscramble the data preceding looking at the decoded data, bringing about increments in time and expenses for the data recovery and (Poh et al. 2017) . Access control models have additionally been utilized to direct and restrict access to the data, in light of predefined get to policies. Such models can be especially successful for outside assaults, however, commonly ineffectual against inside attackers as they are probably going to be approved to get to the data (Alam et al. 2017; Li et al. 2013) . The attributed based encryption is another solution that integrates access control with some cryptographic primitives (Xu 2016; Niranjanamurthy et al. 2018) . However, such a method does not achieve all concerns of security with acceptable (Dinh et al. 2018; Ocheja et al. 2019; Shahzad and Crowcroft 2019; Turkanovic et al. 2018 ) computational efforts. The conventional centralized solutions may get compromised during the online data processing systems (Kshetri and Voas 2018; Chen et al. 2018a) , thus the recent decentralized approach called blockchain gains significant interests since from last five years.

The blockchain is an answer to all the challenges of other centralized security solutions of data storage and sharing in cloud computing (Knirsch et al. 2019; Pirtle and Ehrenfeld 2018) . It is a new paradigm of data documentation on the internet. The blockchain can be used in applications such as voting systems, online shopping, social networks, games (Scriber 2018; Esposito et al. 2018) , storage platforms (like cloud computing), messengers, prediction markets, and online education (Kshetri 2018; Alhayani and Abdallah 2020) . The data considered in blockchain can be of any form such as medical reports sharing, money transfer, individual's identity, ownership (Alhayani and llhan 2021; Alhayani et al. 2021a), sensitive information. Figure 2 illustrates the step by step working of blockchain technology, and Fig. 3 shows the same technology using the cryptography structure (Al-Hayani and Ilhan 2020; Kwekha- Rashid et al. 2021) .

As observed in the figures, it noticed that in blockchain the information does not keep at a central point like the conventional security methods (Hasan and Alhayani 2021; Yahya et al. 2021 ; Abu-Rumman 2021; Abu-Rumman et al. 2021). The multiple copies of similar data are stored in various locations and on various devices, and hence it is called distributed technology (Aldiabat et al. 2018 (Aldiabat et al. , 2019 . As the multiple copies of the same data available, the loss of any single point of storage does not affect the security of the original data Chen et al. 2019) . Also, if the attacker hacks and changes the data at one point, there are multiple similar copies of the same data available to fetch the true data. Zhao et al. 2018 ) In short, the data packaged into different a block that links to build the chain with other blocks of the same information (Kamel Boulos et al. 2018; Zhou et al. 2018) . A blockchain is a process of linking various blocks into the chain that makes the information stored securely. Once the chain of block build (Xia et al. 2017a (Xia et al. , 2017b , it is not possible to alter any single block without altering all other blocks, hence it becomes very difficult to compromise the security using blockchain.

Blockchain technologies generally are three types such as public blockchain, private blockchain, and Federated blockchain.

(a) Public Blockchain The public blockchain technology is available for everyone publically as the name indicates. In the public blockchain, there is no need for taking permission to become part of the public blockchain (Xia et al. 2017b; Gao et al. 2018) . In a public blockchain, any kind of transaction is valid for all the end-users (Zhang et al. 2018b; Chen et al. 2018b ).

(b) Private Blockchain This type of blockchain exactly opposite to the public blockchain as it is a centralized system. However, the security threat risk higher in this blockchain technology (Tian et al. 2019; Rathee et al. 2020) . The cost of transactions is less as well as the process of document handling is easier using a private blockchain. The well-known private blockchain technologies are MONAX and Multichain. Figure 4 shows the difference in working between private and public blockchain technologies (Rocha et al. 2020; Jmaiel et al. 2020 ). (c) Federated Blockchains It is also known as Consortium Blockchains that is opposite to the public blockchain as accessing does not allow everyone. The leader's group process these kinds of blockchains. The privacy Fig. 2 Step-by-step blockchain working 

Due to the advantages of emerging blockchain technology over the conventional security solutions for online data processing (https:// www. kaggle. com/ allen-insti tutefor-ai/ CORD-19-resea rch-chall enge, https:// www. kaggle. com/ sudal airaj kumar/ novel-corona-virus-2019-datas et), a recent number of researchers presented their blockchainbased solutions across different applications. This section presents the review of such methods in two groups Mahajan and Badarla 2018) . In the first group, blockchain-based solutions for all other applications except the healthcare reviewed in section A. In the second group Badarla 2019, 2020) , the blockchain-based solutions for healthcare application reviewed in section B.

As the blockchain is under development technology, there is no full-fledged application and implementation presented so far. Recently few authors attempted to design blockchain for applications like e-learning, e-voting. Initially, several malicious activities and frauds that can be tackled using the blockchain method presented in Mikhail et al. (2017a) . They presented the suggestions for future research into the methods of protecting the malicious activities related to the blockchains. Similar to Mikhail et al. (2017b) , another study on blockchain presented in Alhayani et al. (2021b) in which the definition of blockchain presented, types of blockchain, working of blockchain, and SWOT analysis of blockchain introduced. They also presented the advantages and challenges of using blockchainbased on the SWOT analysis. In (Dinh et al. 2018) , the author presented the study to understand and estimate the future directions of using the blockchain. They designed the block bench framework to understand the performance of the private blockchain against the workloads of data processing. They evaluated three different blockchains such as Parity, Ethereum, and Hyper ledger Fabric on block bench. In the results, they highlighted the trade-offs in design space and performance differences among database systems and blockchain. The study presented in Xu (2016) In Ocheja et al. (2019) , the author presented the framework called blockchain of learning logs (BOLL) to move the students their study records starting with one organization, then onto the next in a verifiable and secure manner to address the cool beginning issue in learning frameworks. The BOLL framework allowed access to learning logs from other institutions to the existing learning data analytic stages according to the learners and/or institution permission. However, BOLL was introduced at the initial level without considering the challenges of scalability and reliability.

In Shahzad and Crowcroft (2019) , another recent blockchain-based framework was introduced to secure the electronic voting system. They presented a framework based on successful hashing techniques to guarantee data security. Further, the methodology of black creation and fixing presented to address the requirement of the polling process. They introduced the consortium blockchain to ensure that the blockchain was owned by the election commission only. However authors presented only a conceptual framework Fig. 4 Public vs. Private blockchain without its validation and implantation, also they considered the assumptions of human awareness which is not the case in real-time scenarios.

In Turkanovic et al. (2018) , the blockchain-based education system introduced called EduCTX. The EduCTX in light of the idea of the European Credit Move and Aggregation Framework (ECTS). They presented the environment prototype implementation using the Ark Blockchain platform. They mentioned that EduCTX will process, oversee, and control the ECTX tokens that demonstrate the student credits gained from course completion. Similar to the limitations of Shahzad and Crowcroft (2019) , this approach also suffered from those issues.

Similar to Shahzad and Crowcroft (2019) , another blockchain-based E-voting system introduced in Kshetri and Voas (2018) called Blockchain-enabled e-voting (BEV). They presented the study of various BEV implementations and their challenges. They summarized their study with the advantages of BEV over the conventional voting process without actually any design and implementations for it.

In Chen et al. (2018a) , the author presented various applications of education and the use of a blockchain framework to address some problems of such applications. They presented the advantages and working of blockchain technology. They reviewed some blockchain-based applications with their advantages for education.

In Bistarelli et al. (2019) , the author proposed the decentralized start to finish casting a ballot stage dependent on the blockchain innovation. They designed the e-voting system using the Bitcoin and Multi Chain systems with a similar underlying concept as a transaction among the voter and competitor speak to a vote, which is communicated to the distributed network and confirmed by diggers. They introduced the arrangement which is completely agreeable with the existing Bitcoin network. They explore several other concepts with few implementations, however missing the validations and analysis.

In Knirsch et al. (2019) , the author presented the blockchain technology with its core concepts by considering the real-time test case of the energy domain. They attempted to implementation of the custom, permissioned, and private blockchain from scratch. However, this is also just another initial study as other literature discussed above without having some real implementations and validations with conventional solutions. Most of the above works were introduced either as a study of blockchain or applications such as e-voting and e-learning oriented research. But all those studies are at just initial level.

In our case, we mainly focused on securing the healthcare systems from unauthorized access, data leakages, and data loss problems. This section reviews the recent technology blockchain-based solutions for healthcare systems. As the blockchain is a relatively new concept, there is not much work reported. In Pirtle and Ehrenfeld (2018) , the introductory information presented over the utilization of blockchain in the social insurance systems by describing the several concerns of medical reports using the blockchain. They summarized that blockchain in its present state doesn't offer the total responsibility for the majority of the present medicinal record tribulations.

In Scriber (2018) , the literature review was presented by considering the healthcare application. They conducted the interviews with companies that using blockchains and evaluated the 23 implementation projects of blockchain at Cable Labs and noticed the observations and questions.

The problem of security becomes severe in the case of a cloud-based environment, thus the recent study presented in Esposito et al. (2018) that used blockchain technology to verify the medicinal services data put away in a cloud. They presented the various challenges of using blockchain technology in the cloud computing paradigm. The work is at the prime level and hence very difficult to figure out the claims. A similar study presented in Kshetri (2018) , they presented how the blockchain may overcome the challenges of healthcare data security and address the problems of conventional cryptography methods. Both studies (Esposito et al. 2018; Kshetri 2018 ) presents a conceptual framework with its advantages and challenges of its implementation, however, there are not validations.

In Alhayani and Abdallah (2020) , the first proper methodology presented in which the design and analysis of blockchain-based securing healthcare data in cloud servers are presented. They designed a blockchain-based accessible encryption method for the EHRs. The EHRs file constructed using the mind-boggling rationale articulations and afterward put away in blockchain such a way that users can exploit the expressions to index searching. They justified the use of blockchain in terms of assurance of integrity, traceability of EHRs, anti-tampering, etc. They validated the method in terms of document IDs extraction from EHRs overhead and smart contract transactions in Ethereum overhead.

In Alhayani and llhan (2021) , another approach of parallel PHSs utilizing the Fake frameworks, Computational analyses, Parallel execution called ACP proposed. The artificial intelligence was used for the decision-making process in patients' diagnosis and treatment process. They additionally used the blockchain methodology using constructing a consortium blockchain connecting patients, wellbeing authorities, hospitals, and the medicinal services networks for secure medical data storage and sharing. In Alhayani et al. (2021a) , the author introduced a methodology in which they merged Body Sensor Network (BSN) with the wellbeing blockchain, and utilize the biosensor nodes in the BSN to propose a lightweight reinforcement and effective recuperation plot for keys of the wellbeing blockchain. The biosensor nodes were utilized to age, reinforcement, and recuperation of wellbeing blockchain keys. Each block was encoded by a recognized key with minimum storage cost and higher security.

In Al-Hayani and Ilhan (2020), the author proposed the novel methodology for securing the clinical data with scalability. They presented four key steps of using the blockchain to the medical data sharing such as (i) they analyzed requirements of health information technology and their implications for the blockchain-based frameworks, (ii) then they proposed the blockchain-based framework to address those requirements called Quick Medicinal services Interoperability Assets (FHIR) Chain called FHIR Chain for shared clinical data, (iii) they demonstrated FHIR Chain using the digital health identities to authenticate, and (iv) they finally noticed the key findings from the case study conducted.

In Kwekha-Rashid et al. (2021) , another study-based invention presented over the blockchain system for the healthcare systems. They presented the promises, challenges, and scenarios in healthcare systems using the geospatial blockchain along with the future directions. In Hasan and Alhayani (2021) , the author proposed a blockchainbased medical insurance storage framework called MI Store. They designed the MI Store framework with key features such as decentralization, secure data storage, threshold, verifiable, efficient verification, and efficient homomorphic computation.

Some other recent works (Yahya et al. 2021; Abu-Rumman 2021; Abu-Rumman et al. 2021; Aldiabat et al. 2018 Aldiabat et al. , 2019 Rashid et al. 2021; Chen et al. 2019; Wang et al. 2018; Zhao et al. 2018; Zhang et al. 2018a ) reported those are based on blockchain for the medical data storage and sharing in the cloud computing environment. The blockchain-based data-sharing framework proposed in Yahya et al. (2021) that adequately approaches the access control difficulties connected with sensible medical data collected in the cloud employing built-in and immutability independence features of the blockchain. They used strong cryptographic methods to guarantee effective access control for shared data pool(s) applying a permission blockchain. Furthermore, produce a blockchain-based data-sharing system that allows data owners to obtain automated medical reports from a shared repository following their individualities with verified cryptographic keys. The MeD Share proposed in Abu-Rumman (2021) to tackle the problem of healthcare data sharing between pharmaceutical big data escorts in trust-less conditions. The blockchain technology applied to achieve the data auditing, data provenance, and control for shared data in cloud containers among big data substances. In Abu-Rumman et al. (2021) , the preceding investigation on the description of Post-Quantum Blockchain (PQB) and designed a secure cryptocurrency system using PQB, that maintain quantum computing threats given. The Trustworthy Keyword Search scheme over Encrypted data without any third party (TKSE) using blockchain proposed in Aldiabat et al. (2018) . In TKSE, the encrypted data index based on digital signature enables an end-user to explore the outsourced encrypted data and examine whether the search outcome delivered by the cloud meets the pre-specified search conditions. Lately other recent methods on blockchain-based security measures and related surveys were presented in Aldiabat et al. (2019) , Rashid et al. (2021) , Chen et al. (2019) , Wang et al. (2018) , Zhao et al. (2018) , and Zhang et al. (2018a) . In Kamel Boulos et al. (2018) , the new methodology utilizing ordinary data stockpiling and security capacities for EHRs had proposed. They planned a blockchain-based framework to address medical data honesty and upgrade framework interoperability. The blocks were made utilizing a novel motivator method. Nonetheless, this methodology didn't perform activities like medical data stockpiling, sharing, and searching under different dangers. The united structure of blockchain and distributed computing had proposed in Zhou et al. (2018) for privacy protection of medical data connections with cloud and blockchain. They planned a technique for distributed computing and its connection with blockchain hubs to play out the safe medical data activities.

This section presents the proposed system model for healthcare monitoring using blockchain and cloud computing. Then the experimental results using existing methods are discussed. Finally, the research gaps, challenges, and future roadmaps are discussed.

The system model of proposed Healthcare 4.0 assisted medical data processing in connection with CSP and blockchain technologies have been presented in this section. Figure 5 shows the proposed united structure by considering all the essential advancements of arising Healthcare 4.0. The connections between the parts are bidirectional for handling the send and get activities of collected medical data. The proposed system comprises five parts like data proprietor (IoT hub or patient), medical client, fog hubs, CSP, and blockchain. On the opposite side, Fig. 1 likewise shows the layers of Healthcare 4.0 innovation, for example, edge layer, fog layer, cloud layer, and blockchain layer. The edge layer comprises an assortment of IoT gadgets like Wireless Body Area Network (WBAN) hubs, mobiles phones, PCs, and so forth. Fog layer is fog registering administrations in which activities of data focuses are relocated into fog hubs to diminish data transmission time with high data rates. The Cloud layer performs activities of data stockpiling, at long last blockchain layers answerable for circulated capacity of CSP meta-data and logs in the chain of various blocks. Supposedly, this is the primary endeavor that characterized the four layers for Healthcare 4.0 applications.

The design is shown in Fig. 5 proposing a Healthcare 4.0 assisted safe smart healthcare system. Consequently, we effectively defined elements and their communications in the proposed model. At first sight, the medical data sensed by body sensor nodes installed on each patient's body has already been registered and verified with the smart hospital practice. The sensed data then encrypted and transmitted to the fog nodes. At fog nodes, collected data verified, and then transmitted to CSP storage including indexing. The access log and meta-data has produced for every incoming encrypted data from the victims and saved into distributed private blockchain for effective security goals against the different vulnerabilities. The proposed system model consists of five components such as IoT Node (IN), Medical User (MU), Fog Node (FN), Cloud Storage (CS), and Private Blockchain (PB). A next section presents the two important operations of this model such as medical data storage and sharing.

This section presents the implementation and results of using existing method for proposed system model showing in Fig. 5 . The proposed model had implemented on Windows 10 OS with 4 GB RAM and Intel® Core i5 processor.

The programming language Java used with Netbeans IDE. For all the cryptographic operations, we used Java security library, Bounty Castle libraries, and Java Pairing-Based Cryptography (jPBC). For the CS node, we designed the Amazon Web Services (AWS) called Amazon S3. The Java AWS SDK (Software Development Kit) has been used to allow the CS node functionality of the proposed model and state-of-art models. The FN had implemented using virtual functions to understand their functionality in the proposed model. For the PB node, we designed the Hyperledger blockchain network in the Docker background with node.js. The PB node consists of two peer nodes, the order node, and the endorser node. For comparative analysis, searchable symmetric encryption (SSE)-based method called TKSE (Aldiabat et al. 2018) , Proxy Re-Encryption Scheme (PRES) (Kamel Boulos et al. 2018) , and Proxy Re-Encryption using RSA (PRER) (Zhou et al. 2018 ) have been implemented. We compare the performance of the proposed model using these three state-of-art techniques by varying the data size with a fixed number of medical users 20. The medical data are generated from these sources periodically with help of publically available research datasets of Covid-19 disease (Xia et al. 2017a (Xia et al. , 2017b . Figure 6 (Table 1) and Fig. 7 (Table 2) shows the results of average encryption and average decryption time using each method by varying the data size. Figure 7 shows the outcome of both encryption and decryption time considering all the scenarios. The result of encryption and decryption time for every system with changing data size reveals that there a fast improvement in execution time as the medical data size increases to sparse MB's. Among the existing methods, 1024 bits PRER and TKSE have shown the worst results due to using RSA and symmetric-key encryption mechanisms respectively compared to PRES. Figure 8 shows the summed outcomes for varying data size scenarios of every cryptography method. The proposed method shows that encryption time decreased by approximately 400 ms and decryption time decreased by 350 ms approximately.

As discussed earlier, the blockchain-based solutions gained the researcher's interest to overcome the problems of conventional cryptographic and access control methods to tackle the privacy and security challenges, especially in the cloud computing environment. In the above sections, we present the review of all the recent blockchain-based methods that are studied, modeled, or designed for a specific application like e-voting, e-learning, and e-healthcare. During the study, we noticed the significant research gaps and further challenges to design and implement the blockchain-based approach for medical data storage and sharing in the cloud computing environment. The key requirements of medical data processing using cloud computing are secure data storage, secure data sharing, and efficiency. The current solutions do not achieve the trade-offs among storage, sharing, and efficiency. The efficiency is measured in terms of scalability, computational efforts, and security. First, we summarize the research gaps in methods studied in Pirtle and Ehrenfeld (2018) 

1. The current methods introduced for healthcare applications are not sufficient to address the challenges of medical data storage and sharing using the blockchain approach as they were designed with specific goals. 2. The encryption methods used in some blockchain-based security models not effective and scalable to support large-scale real-time medical data. 3. Most of the methods introduced the models without the evaluations with state-of-art methods or similar methods, in short, complete security and performance analy- 

Overall encryption and decryption time for varying data size scenario sis missing to justify the effectiveness of blockchainbased healthcare systems.

including the post-quantum threats unavailable in all the blockchain-based methods and hence it is confusing to justify the security benefits at a practical level. 5. Lack of study that practically shows the achievement of features of the blockchain system such as privacy, user side verifiability, server-side verifiability, payment fairness, no third party, compatibility, and performance efficiency

As discussed earlier, along with key features consideration while designing and implementing the blockchain-based healthcare system the challenges related below terms needs to address:

• Data storage: As there is a large number of medical patients and hospitals connected in EHRs, there should be computationally efficient and strong security-based cryptography algorithm required to form the blockchain model. • Data sharing: The blockchain model should consider the possibility of various threats including quantum threats as well while performing medical data sharing. • Efficiency: The key requirement of the blockchain model is performance efficiency in terms of scalability, computational burden, and security. The model should be scalable with minimum computation overhead.

By considering the above research gaps and challenges, the probable future roadmap should focus on development of below solutions to optimize the design of healthcare 4.0 for smart city perspective.

• Quantum aware blockchain (QAB): The goal is to protect the blockchain functionality from quantum computing threats while performing the medical data processing with CPS. The post-quantum cryptography algorithm can be based on the lattice cryptography technique to reduce the public key, private key, and signature sizes and addressing strong security against the quantum threats in blockchain to secure the medical data. • Medical data storage using QAB: The consolidated framework QAB can formulate for two research problems such as scalable medical data storage and trustworthy keyword search over the encrypted data storage. For this phase, the post-quantum cryptography algorithm will encrypt and store data on the blockchain via cloud servers. • Medical data search using QAB: The consolidated framework of QAB can be designed to address the challenge of efficient keyword search problem in e-healthcare. The approaches of the search request, commitment, decryption, etc. designed using the novel post-quantum cryptography algorithm. • Extensive performance evaluations: Implementation and evaluations of proposed techniques with varying number of users and varying data sizes in presence of quantum threats and commonly occurred threats to justify the effectiveness and efficiency will be the final roadmap in this domain.

Nowadays, most healthcare organizations do not have the facility to protect the patient's data from unauthorized access, and hence present EHRs may fail to meet the privacy requirements of patients. The emergence of Healthcare 4.0 using the technologies Internet of Things (IoT), Cloud computing, Big data, and blockchain has required to deal with security challenges for medical data processing. Various centralized cryptography solutions were introduced to secure such data, however, they failed to address the problems completely. In this paper, we introduced blockchain technology that may overcome the challenges of providing EHRs security based on the review of recent works. We presented the model of EHRs first, then the applicability of blockchain in EHRs along with its benefits. The study was conducted on recent works reported in the last few years for blockchainbased security and noticed the various research gaps and challenges. For future work, we suggest proceeding in the direction that considered the research gaps, challenges, and future roadmaps discussed in this paper .

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