Fluent Essays

Complete  a review of the attached article by writing a 2-3 page overview of the  article. This will be a detailed summary of the journal article,  including concepts discussed and Applications in Health Care. Additionally, find one other  source (2nd - Health_Care.pdf) that substantiates the findings in the article you are reviewing.   Once you find the article, you will read it and write a review of it.  This is considered a research article review. Your paper should meet these requirements:   Be approximately 5 pages in length, not including the required cover page and reference page. Follow APA 7 guidelines. Your paper should include an introduction, a body with fully developed content, and a conclusion. Support  your answers with the readings from the course and at least two  scholarly journal articles to support your positions, claims, and  observations, in addition to your textbook. Received July 7, 2019, accepted July 28, 2019, date of publication August 19, 2019, date of current version September 4, 2019. Digital Object Identifier 10.1109/ACCESS.2019.2936094 A Survey of Blockchain From the Perspectives of Applications, Challenges, and Opportunities AHMED AFIF MONRAT , OLOV SCHELÉN, (Member, IEEE), AND KARL ANDERSSON , (Senior Member, IEEE) Department of Computer Science, Electrical and Space Engineering, Lulea University of Technology, 931 87 Skelleftea, Sweden Corresponding author: Ahmed Afif Monrat ([email protected]) The financial support for the research is provided by the Swedish Energy Agency under Grant 43090-2, and in part by the Cloudberry Datacenters. ABSTRACT Blockchain is the underlying technology of a number of digital cryptocurrencies. Blockchain is a chain of blocks that store information with digital signatures in a decentralized and distributed network. The features of blockchain, including decentralization, immutability, transparency and auditability, make transactions more secure and tamper proof. Apart from cryptocurrency, blockchain technology can be used in financial and social services, risk management, healthcare facilities, and so on. A number of research studies focus on the opportunity that blockchain provides in various application domains. This paper presents a comparative study of the tradeoffs of blockchain and also explains the taxonomy and architecture of blockchain, provides a comparison among different consensus mechanisms and discusses challenges, including scalability, privacy, interoperability, energy consumption and regulatory issues. In addition, this paper also notes the future scope of blockchain technology. INDEX TERMS Blockchain, distributed ledger, consensus procedures, cryptocurrency, smart contract, selfish mining, energy consumption. I. INTRODUCTION Unlike traditional methods, blockchain enables peer-to-peer transfer of digital assets without any intermediaries [1]. Blockchain was a technology originally created to support the famous cryptocurrency Bitcoin. Bitcoin was first proposed in 2008 and implemented in 2009 by Nakamoto [2]. Since then, it has seen huge growth with the capital market, reaching 10 billion dollars in 2016. Blockchain is basically a chain of blocks that store all committed transactions using a public ledger [3]. The chain grows continuously when new blocks are appended to it. Blockchain works in a decentralized environment that is enabled by comprising several core tech- nologies, such as digital signatures, cryptographic hash, and distributed consensus algorithms. All the transactions occur in a decentralized manner that eliminates the requirement for any intermediaries to validate and verify the transactions [4]. Blockchain has some key characteristics, such as decentral- ization, transparency, immutability, and auditability [5]. Although Bitcoin is the most famous application of blockchain, it can be applied to diverse applications far beyond cryptocurrencies. Since it allows payments to be The associate editor coordinating the review of this article and approving it for publication was Chien-Ming Chen. finished without any bank or any intermediary, blockchain can be used in various financial services, such as digital assets, remittance and online payment [6]. The blockchain itself has taken on a life of its own and permeated a broad range of applications across many industries, includ- ing finance, healthcare, government, manufacturing, and distribution [7]. The blockchain is poised to innovate and transform a wide range of applications, including goods transfer (supply chain), digital media transfer (sale of art), remote services delivery (travel and tourism), plat- forms for example, moving computing to data sources and distributed credentialing [8]. Additional applications of blockchain include distributed resources (power generation and distribution), crowdfunding, electronic voting, Identity management and governing public records. Despite the fact that blockchain technology shows great potential that may replace many of the current digital plat- forms, it has some technical constraints. Scalability is a huge concern for blockchain based platforms [9]. In Bitcoin, the limited size and frequency of the blocks along with the number of transactions the network can process can be con- sidered a scalability problem [10]. The average block creation time in Bitcoin is 10 minutes, and the block size is limited to 1 megabyte which constrains the network’s throughput [11]. 117134 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see http://creativecommons.org/licenses/by/4.0/ VOLUME 7, 2019 https://orcid.org/0000-0001-9801-7625 https://orcid.org/0000-0003-0244-3561 A. A. Monrat et al.: Survey of Blockchain From the Perspectives of Applications, Challenges, and Opportunities Bitcoin’s ability to scale depends on the size of the block and is limited to the complexity of the mathematical puz- zle independent of the nodes in the network. In general, the transaction processing capacity of Bitcoin is between 3.3 to 7 transaction per second [12]. However, due to the increased size of recently generated blocks, the transaction throughput is being effectively limited to 2-4 transactions per second, which is incapable of high-frequency trading. At present, there are more than 36 million wallet users, and with time, it will increase and create an adverse impact on the network’s throughput. Different issues such as the blockchain congestion problem, transaction delays, and increased trans- action fees will raise concerns. As a result, the technology may not be a sustainable approach for government or private sectors to build their business model upon the blockchain platform. Moreover, increased block size requires substantial storage space and cause slower propagation in the blockchain network [13], which will also lead towards centralization and trust issues as users would like to operate and maintain such a large blockchain. Therefore, it has become a great challenge to deal with the tradeoff between blockchain size and trust. Blockchain has some other issues regarding interoper- ability, privacy, energy consumption, selfish mining, secu- rity, and regulation policy. The interoperability issue arises due to the lack of standard protocol for adopting and integrating blockchain-based solutions among companies. Privacy leakage may also happen within the blockchain, although the system claims to be extensively secured as users only make transactions with digital signatures that associate public-private key encryption [14]. Furthermore, it is possible to track the user’s real IP address. Consensus mechanisms such as proof-of-work (PoW) and proof-of-stake (PoS) are also facing serious concerns. For instance, PoW is known for consuming a large extent of electrical energy due to the competitive nature of miners for creating blocks by solving complex mathematical puzzles [15]. In PoS, the rich become gradually richer as the chance of obtaining a block depends on how much stake the miners have [16]. Another drawback of blockchain technology is selfish mining, where miners can gain better revenue than their fair share by keeping their blocks private [17]. Blockchain can also suffer from 51% attacks, where some node attains the majority in a network and abuses it. Furthermore, it is believed that blockchain technology may not reach its peak or anticipated large-scale adoption by stakeholders because of uncertainties that arise with potential government regulations [18]. One of the major underlying reasons could be that the decentralized nature of blockchain eliminates intermediary links to central banks to control the economy, which does not bode well with the government. Hence, some measures need to be put forward to address these issues in blockchain. This survey paper focuses on state-of-art blockchain stud- ies including blockchain architecture, consensus algorithms, applications of blockchains, trade-off and challenges. The rest of this survey paper is organized as follows. Section II introduces blockchain architecture. Section III shows typical consensus algorithms used in the blockchain. Section IV introduces several typical blockchain applications. Section V summarizes the tradeoffs and technical challenges, in this area. Section VI discusses some possible future directions and Section VII concludes the paper. II. BLOCKCHAIN ARCHITECTURE A node initiates a transaction in a decentralized blockchain network by employing a digital signature using private key cryptography. A transaction can be considered as a data struc- ture that represents transfer of digital assets between peers on the blockchain network. All the transactions are stored in an unconfirmed transaction pool and propagated in the network by using a flooding protocol known as Gossip protocol. Then, peers need to choose and validate these transactions based on some preset criteria. For example, the nodes try to verify and validate these transactions by checking whether an initiator has sufficient balance to trigger a transaction or by trying to fool the system by enforcing double spending. Double spending refers to using the same input amount for two or more different transactions [19]. Once the transaction is verified and validated by the miners, it is included in a block. Peers who use their computational power to mine for blocks are called miners [20]. Miner nodes need to solve a computa- tional puzzle and spent a sufficient amount of their computing resources to publish a block. The miner who can solve the puzzle first will become a winner and obtains the opportunity to create a new block. A small amount of incentive is given upon successfully creating a new block. All the peers in the network then verify the new block using a consensus mechanism, which is a technique that assist a decentralized network comes to an agreement on certain matters. After that the new block will be added to the existing chain and the local copy of each peer’s immutable ledger. At this point, the trans- action is confirmed. The next block links itself with the newly created block by using a cryptographic hash pointer. Now the block obtains its first confirmation while the transaction obtains the second confirmation. Similarly, with every time a new block is appended to the chain, the transaction will be reconfirmed. In general, a transaction needs six confirmations in the network to be considered final [21]. Later in this segment, Section II-A discusses the trans- action process of blockchain with some example platforms, such as Bitcoin and Ethereum, Section II-B introduce the basic block structure and the process of cryptographic hash functions while Blockchain key characteristics are explained in Section II-C and Section II-D represents the taxonomy of blockchain. A. BLOCKCHAIN TRANSACTION PROCESS A Blockchain transaction can be defined as a small unit of a task that is stored in public records. These records are also known as blocks [22]. These blocks are executed, imple- mented and stored in blockchain for validation by all miners involved in the blockchain network. Each previous transac- tion can be reviewed at any time but cannot be updated [23]. VOLUME 7, 2019 117135 A. A. Monrat et al.: Survey of Blockchain From the Perspectives of Applications, Challenges, and Opportunities FIGURE 1. Functional diagram of a Blockchain network. Blockchain is the underlying technology of Bitcoin, and it facilitates transactions that occur within a peer to peer global network in a decentralized fashion. That makes Bitcoin a borderless, censorship-resistant digital currency. In general, trust may be the main concern regarding traditional central- ized systems, such as a banks, where people need to put their solemn confidence in the system. This is the sweet spot for public blockchain technology, in that it does not require any trust while handing over the ownership of digital assets from one peer to another. Blockchain is a trustless system that provides trust through the functions that propagate all the activities within the network [24]. Security is another aspect to consider while initiating transactions. Blockchain mining and consensus mechanisms that rely heavily on a cryptographic hash function can address the security issues. For example, Bitcoin uses a 256 bits’ secure hash algorithm known as SHA-256 [25]. Bitcoin can take any type of input, such as text, numbers, string or even a computer-generated file of any length, to produce 256 bits or the 64 characters output called hash [26]. Given the same input, the converted hash output will always remain exactly similar. However, a small change to the input will change the output completely, which is also called a one-way function, meaning that from the output, it is not feasible to calculate the input. One can only guess what the input was, and the odds of guessing it right are rather astronomical, in other words, it is secure. The first step of the transaction process is to verify the identity of the sender, which means the transaction between the sender and the receiver is requested by the sender, and not by anyone else. Figure 2 demonstrates the verification pro- cess with a simple example of a transaction between Bob and Alice. Let us assume both Alice and Bob has Bitcoin balance, and Alice wants to pay 10 Bitcoins to Bob. Now, to send the money, Alice will broadcast a message with the information for the transaction in the blockchain network. To do this, Blockchain employs digital signatures (public and private keys) [27]. For the broadcast, Alice provides Bob’s infor- mation, such as his public address and transaction amount, along with her public key and digital signature. Alice used her private key to make that digital signature. Transaction validation is carried out independently by all miners based on different criteria that we have discussed later in this section. Elliptic curve digital signature algorithm (ECDSA) is used by blockchain [28]. This algorithm ensures that the funds can only be spent by their true possessors. The signature in each transaction contains 256 bits, if any- one wants to fake this signature to make a fraudulent transac- tion, he or she has to guess 2256 cases, which is infeasible and waste of resources for a malicious peer/attacker [29]. In addition to checking the validity of the sender, the verifier also has to check the validity of the transaction regarding whether the sender has enough money to send to the receiver, or not. It could be performed by looking at the ledger, which holds information about every past successful transaction. 1) BITCOIN TRANSACTION According to the original Bitcoin whitepaper, the main pur- pose of this digital cryptocurrency was to allow a decen- tralized electronic cash payment system between different parties by eliminating central intermediaries [30]. A Bitcoin transaction transfers the ownership of some bitcoin amount to another bitcoin address. Generally, it is initiated by a bitcoin wallet of a client and later broadcast to the network. The nodes on the network will rebroadcast the transaction and include it in the block they are mining only if the transaction is valid. It takes approximately 10 minutes to include the 117136 VOLUME 7, 2019 A. A. Monrat et al.: Survey of Blockchain From the Perspectives of Applications, Challenges, and Opportunities transaction along with other transactions in a block [31]. The receiver should see the amount of transaction in their wallet by this point. The main element of a bitcoin structure is unspent trans- action output (UTXO), which refers to the output amount of a transaction that is received by a user and the capability of spending it in the future [32]. Consider that cash or coins in a physical wallet get mixed up, which is not in the case of the received amount in Bitcoin. All the received amount in a Bitcoin wallet remains as a separate entity. For example, when we receive two distinct amounts ($2 and $3) and keep it in the same physical or online wallet, it will obtain summed up to $5. Whereas in the Bitcoin wallet, it will still show the exact amounts and remain as individual entities. Let us consider that Alice has three separate UTXO (0.01, 0.2 and 3) in her wallet, and she wants to send 0.15 BTC to Bob. To do that, the wallet needs to select a spend candidate from these three output UTXO. If the wallet chooses 0.2 as an output, then it will unlock this amount and spend the whole amount as an input UTXO for the 0.15 BTC transaction. Then, 0.15 BTC will be transferred to Bob’s address wallet as an output UTXO. Miners will be incentivized by their effort in managing and validating all these transactions and creating a new block that will eventually add to the existing chain [33]. A successful miner obtains the block creation rewards and transaction fees [34]. While sending transactions, users usually assign a transaction fee upon successful block creation for the miners. There will not be any header information regarding the trans- action fee. The users can attach a transaction fee by sending a lesser amount to the recipients than the total input UTXO. This unassigned transaction amount can be considered as transaction fee as depicted in Eq. 1. Inputs−outputs = Transactionfees (1) Miners include their individual coinbase transaction along with the transaction data that they are trying to verify and validate while mining a block. A coinbase transaction is a unique type of bitcoin transaction that can only be created by a miner. This type of transaction has only outputs, and there is one created with each new block that is mined on the network. This is the transaction that rewards a miner with the block reward for their work. Any transaction fees collected by the miner are also sent in this transaction. The peers in the network check whether the transaction is level out and then decide to put this record in the distributed ledger. The coinbase transaction will send the block reward and the sum of the transaction fees to the given address of the miner. That shows that a miner has to assign his reward while creating a block. However, every node in the network will check whether the block adheres to the requirement, and as shown in Eq. 2. Therefore, a miner is eligible to use the block reward and transaction fees only after the block is verified. sum(BlockOutputs) ≤ sum(BlockInputs)+BlockReward (2) 2) ETHEREUM TRANSACTION The Bitcoin state is defined in the terms of UTXO, a ref- erence implementation of the wallet application that held the account reference. However, Ethereum introduced the concept of an account as a part of the protocol that is the originator and target of a transaction. Hence, transactions directly update the account balances as opposed to main- taining the state, such as in the Bitcoin UTXOs, allowing transfer of values, messages and data between the accounts that may result in the state transitions [35]. Ethereum has two types of account: Externally Owned Account (EOA) and Contract Account (CA). While EOA is owned by private keys, CA is controlled by the code and activated only by an EOA [36]. EOA is needed to participate in the Ethereum network and interacts with the blockchain using transactions, whereas, CA represents a smart contract (SC). SC is a piece of code deployed in the blockchain’s node and adds a layer of logic and computation to the trust infrastructure [37]. Exe- cution of an SC is initiated by a message embedded in the transactions. In Ethereum, the transferable amount is known as ether. The denomination of ether is known as Wei [38]. An Ethereum transaction has fields for transferring ether as well as messages to trigger smart contracts [39]. Ethereum uses attributes similar to Bitcoin, for instance, previous block hash, nonce, and transaction details. Additionally, it uses some other fields such as fees limit, state of SC, and so on. For a simple ether transfer, the amount to transfer and the target address are specified, together with the fees, gas points, and the respective accounts. All the transac- tions generated will be validated by checking time stamp, nonce combination, and availability of sufficient fees for execution. Ethereum also uses an incentive based model for block cre- ation. Any action in Ethereum requires crypto fuel or gas. Gas is used as fees instead of ether for ease of computation. The main reason behind that is that gas is a cryptocurrency inde- pendent of valuation for the transaction fee and computation fee. Ether, as a cryptocurrency, varies in value with market swings, but gas points do not vary. The mining process com- putes gas points required for the execution of a transaction. If the fee specified in the gas points in transaction is not suf- ficient, it is rejected. The gas points needed for the execution must be in the account balance and the proposed transaction for the execution to happen. The leftover amount after execut- ing the transaction will be returned to the originating account. Etherreum has a mining incentive model where the miners are competing for block creation. The miner who solves the puzzle first is called the winner and the miners who solve it afterwards are called ommers [40]. The winner block is added to the main chain and ommer blocks are added as side blocks in the main chain. The winner block receives three ethers as a base fee along with the transaction fees as gas points. The ommers block receives a small percentage of total gas points. VOLUME 7, 2019 117137 A. A. Monrat et al.: Survey of Blockchain From the Perspectives of Applications, Challenges, and Opportunities B. BLOCK STRUCTURE The Blockchain comprises a sequence of blocks, which stores the information of all the transactions, similar to a public ledger. These blocks are linked to each other via a refer- ence hash that belongs to the previous block known as the parent block. The starting block is called the genesis block, which does not have any parent block. A block consists of the block header and the block body [41]. The block header includes metadata such as block version, parent block hash, Merkle tree root hash, timestamp, nBits, and nonce as shown in Table 1 and Fig. II-B. TABLE 1. Block header attributes. FIGURE 2. Block structure. The block body is composed of a transaction counter and transactions. The transaction counter refers to how many transactions follow, and transactions represent the list of recorded transactions in the block. The maximum number of transactions that a block can contain depends on the block size and the size of each transaction. Blockchain uses an asymmetric cryptography mechanism to validate the authen- tication of transactions. A digital signature based on asym- metric cryptography is used in an untrustworthy environment such as the blockchain network. In this process, each par- ticipant in the network owns a private key and public key pair. The private key is used for signing or encrypting the transaction while the public key is distributed throughout the network and is visible to everyone, which helps to decrypt the following transaction. C. CHARACTERISTICS OF BLOCKCHAIN 1) DECENTRALIZATION In conventional centralized transaction systems, each transac- tion needs to be validated through the central trusted agency (e.g., the central bank). Therefore, decentralization requires trust, which is the main issue, along with lift resilience, avail- ability and fail over, where the decentralized peer-to-peer blockchain architecture could be a better solution. Unlike a centralized system, a transaction in the blockchain network can be conducted between any two peers (P2P) without the authentication by the central agency. In this manner, blockchain can reduce the trust concern by using various consensus procedures. Moreover, it can reduce the server costs (including the development cost and the operation cost) and mitigate the performance bottlenecks at the central server. In contrast, in many cases, blockchain has some trade- offs. For example, PoW cases such as Bitcoin and Ethereum, the server and energy cost are orders of magnitude higher, while the performance are also several orders of magnitude lower. 2) PERSISTENCY Blockchain provides the infrastructure by which truth can be measured [42] and enables the producers as well as con- sumers to prove their data are authentic and not altered. For example, if a Blockchain consists of 10 blocks, then block no. 10 contains the hash of the previous subsequent block, and to create a new block, the information of the current block is used. Therefore, all the blocks are linked and connected with each other in the existing chain. Even the transactions are related to the prior transaction. Now, a simple update on any transaction will significantly change the hash of the block. If someone wants to modify any information, he has to change all the previous block’s hash data which is considered an astronomically difficult task considering the amount of work that needs to be done. In addition, after generating a block by a miner, it is confirmed by other users in the net- work. Hence, any manipulation or falsification of data will be detected by the network. For this reason, blockchain is almost tamper proof and considered as an immutable distributed ledger. 3) ANONYMITY It is possible to interact with the blockchain network with a randomly generated address [43]. A user can have many addresses within a Blockchain network to avoid the exposure of his identity. As it is a decentralized system, no central authority is monitoring or recording users’ private informa- tion. Blockchain provides a certain amount of anonymity through its trustless environment. 4) AUDITABILITY All the transactions that occur in a blockchain network are recorded by a digital distributed ledger and validated by a digital timestamp. As a result, it is possible to audit and trace 117138 VOLUME 7, 2019 A. A. Monrat et al.: Survey of Blockchain From the Perspectives of Applications, Challenges, and Opportunities previous records by accessing any node in the network [44]. For example, all the transactions could be traced iteratively in Bitcoin which facilitates auditability and transparency of the data state in the blockchain. However, by tumbling money through many accounts, it becomes very hard to trace the money to its origin. D. TAXONOMY OF BLOCKCHAIN SYSTEMS There are three types of blockchain: public, private and consortium [45]. These systems can be compared using dif- ferent perspective as described below. 1) CONSENSUS DETERMINATION All the nodes can participate in the consensus process in the public blockchain such as Bitcoin, while only a few selected set of nodes are being responsible for confirming a block in the consortium blockchain. In the private blockchain, a cen- tral authority will decide the delegates who could determine the validated block. 2) READ PERMISSION Public blockchain allows read permission to the users, where the private and consortium can make restricted access to the distributed ledger. Therefore, the organization or consortium can decide whether the stored information needs to be kept public for all or not. 3) IMMUTABILITY In the decentralized blockchain network, transactions are stored in a distributed ledger and validated by all the peers, which makes it nearly impossible to modify in the public Blockchain. In contrast, the consortium and private Blockchain ledger can be tampered by the desire of the dominant authority. 4) EFFICIENCY In the public blockchain, any node can join or leave the network which makes it highly scalable. However, with the increasing complexity for the mining process and the flexible access of new nodes to the network, it results in limited throughput and higher latency. However, with fewer valida- tors and elective consensus protocols, private and consor- tium blockchain can facilitate better performance and energy efficiency [46]. 5) CENTRALIZED The significant difference among these three types of Blockchain is that the public blockchain is decentralized, while the consortium is partially centralized and private blockchain is controlled by a centralized authority. Since public blockchain is open to the world, it can attract many users. Communities are also very active. Many public blockchains emerge day-by-day. For the consortium blockchain, it could be applied to many business applica- tions. Currently, Hyperledger is developing business consor- tium blockchain frameworks. Ethereum has also has provided TABLE 2. Comparison among different blockchain infrastructure. tools for building consortium blockchains. For the private blockchain, there are still many companies implementing it for efficiency and auditability. III. CONSENSUS PROCEDURES In blockchain, how to reach consensus among the untrustwor- thy nodes is a transformation of the Byzantine Generals (BG) Problem [47]. In the BG problem, a group of generals who command a portion of a Byzantine army circle the city. The attack would fail if only part of the generals attack the city. Generals need to communicate to reach an agreement on whether to attack or not. However, there might be traitors within the generals. The traitor could send different decisions to different generals. This is a trustless environment. How to reach a consensus in such an environment is a challenge. It is also a challenge for blockchain as the blockchain network is distributed. In blockchain, there is no central node that ensures ledgers on distributed nodes are all the same. Nodes need not trust other nodes. Thus, some protocols are needed to ensure … Viewpoint Blockchain Applications in Health Care and Public Health: Increased Transparency Pedro Elkind Velmovitsky1, BSc, MSc; Frederico Moreira Bublitz1,2, BSc, MSc, PhD; Laura Xavier Fadrique1, MSc, PMP; Plinio Pelegrini Morita1,3,4,5,6, PEng, MSc, PhD 1School of Public Health and Health Systems, University of Waterloo, Waterloo, ON, Canada 2Center for Strategic Technologies in Health (NUTES), State University of Paraiba (UEPB), Campina Grande, Brazil 3Institute of Health Policy, Management, and Evaluation, University of Toronto, Toronto, ON, Canada 4Research Institute for Aging, University of Waterloo, Waterloo, ON, Canada 5Department of Systems Design Engineering, University of Waterloo, Waterloo, ON, Canada 6eHealth Innovation, Techna Institute, University Health Network, Toronto, ON, Canada Corresponding Author: Plinio Pelegrini Morita, PEng, MSc, PhD School of Public Health and Health Systems University of Waterloo 200 University Ave W Waterloo, ON, N2L 3G1 Canada Phone: 1 15198884567 ext 41372 Email: [email protected] Abstract Background: Although big data and smart technologies allow for the development of precision medicine and predictive models in health care, there are still several challenges that need to be addressed before the full potential of these data can be realized (eg, data sharing and interoperability issues, lack of massive genomic data sets, data ownership, and security and privacy of health data). Health companies are exploring the use of blockchain, a tamperproof and distributed digital ledger, to address some of these challenges. Objective: In this viewpoint, we aim to obtain an overview of blockchain solutions that aim to solve challenges in health care from an industry perspective, focusing on solutions developed by health and technology companies. Methods: We conducted a literature review following the protocol defined by Levac et al to analyze the findings in a systematic manner. In addition to traditional databases such as IEEE and PubMed, we included search and news outlets such as CoinDesk, CoinTelegraph, and Medium. Results: Health care companies are using blockchain to improve challenges in five key areas. For electronic health records, blockchain can help to mitigate interoperability and data sharing in the industry by creating an overarching mechanism to link disparate personal records and can stimulate data sharing by connecting owners and buyers directly. For the drug (and food) supply chain, blockchain can provide an auditable log of a product’s provenance and transportation (including information on the conditions in which the product was transported), increasing transparency and eliminating counterfeit products in the supply chain. For health insurance, blockchain can facilitate the claims management process and help users to calculate medical and pharmaceutical benefits. For genomics, by connecting data buyers and owners directly, blockchain can offer a secure and auditable way of sharing genomic data, increasing their availability. For consent management, as all participants in a blockchain network view an immutable version of the truth, blockchain can provide an immutable and timestamped log of consent, increasing transparency in the consent management process. Conclusions: Blockchain technology can improve several challenges faced by the health care industry. However, companies must evaluate how the features of blockchain can affect their systems (eg, the append-only nature of blockchain limits the deletion of data stored in the network, and distributed systems, although more secure, are less efficient). Although these trade-offs need to be considered when viewing blockchain solutions, the technology has the potential to optimize processes, minimize inefficiencies, and increase trust in all contexts covered in this viewpoint. JMIR Med Inform 2021 | vol. 9 | iss. 6 | e20713 | p. 1https://medinform.jmir.org/2021/6/e20713 (page number not for citation purposes) Velmovitsky et alJMIR MEDICAL INFORMATICS XSL•FO RenderX mailto:[email protected] http://www.w3.org/Style/XSL http://www.renderx.com/ (JMIR Med Inform 2021;9(6):e20713) doi: 10.2196/20713 KEYWORDS health care; blockchain; EHR; health insurance; drug supply chain; genomics; consent; digital ledger; food supply chain Introduction Background Global society is moving into an age of ubiquitous and smart technologies that monitor our health, such as smart devices, Internet of Things solutions, and ambient assisted living systems. These technologies allow continuous and effortless health data collection at a previously unseen scale [1,2], generating rich and massive data sets, known as big data [3]. The age of big data can lead to a change in the way health care is delivered. Generally, health care is reactive, in which individuals interact with health care services when there is something wrong [4,5] and usually to treat acute diseases, instead of proactive, in which real-time monitoring of health data from different sources leads to predictions and insights into individual and population health, as opposed to checkups with health services when a problem appears [4,5]. In this manner, a proactive and predictive health care model includes surveillance and monitoring of individuals through remote sensing technologies, such as smart bands and smart thermostats, generating large volumes of diverse and real-time data in a cost-effective manner. The use of such technologies in a community will also enable public health surveillance on a scale never seen before, allowing public health agencies to better understand the socioeconomic determinants of health and prevent disease outbreaks [5,6]. However, to achieve this model of health care, there are challenges that need to be overcome. For example, health records are stored by different providers in systems that lack interoperability [7,8]. This makes data sharing difficult and prevents doctors from having a complete view of a patient’s health [7,8]. Interoperability issues and costs also affect the availability of genomic data and minimize their benefits [9]. In addition, increasingly advanced methods of data collection and analysis of personal, medical, and genomic data raise concerns regarding ownership, privacy, and regulations of health data [1,3]. One possible tool to overcome or mitigate these challenges is blockchain [6,10-13]. This technology can be seen as a distributed virtual ledger that records timestamped transactions [6,12,13]. Cryptography is used to ensure that when a block is added to the blockchain, it cannot be tampered with [12]. Hence, blockchain is a tamperproof digital ledger in which all participants view an immutable version of the truth, making it ideal to track an asset and enable trust among parties (eg, health data or user consent for data collection) [6,7,12,14]. In 2016 and 2018, IBM Corporation surveyed more than 400 health care and life sciences executives on the use of blockchain technology. Among their findings, more than half of the executives in both industries had plans to adopt it by 2020 [6,10,11]. Given the perceived potential of blockchain by industry experts from multiple areas [6,10-12] and to help guide the implementation of digital solutions that can solve pressing needs in health care systems, the aim of this study is to review current blockchain solutions being developed by the health care industry. This paper provides a comprehensive view of the blockchain health care industry, providing guidance to innovators about how to leverage this technology in daily operations and how to implement solutions that can help evolve health care delivery. The COVID-19 outbreak has created an increased demand for home-based digital health solutions such as telehealth and telemonitoring [15], increasing the importance of using technologies such as blockchain to increase the transparency of digital transactions and data provenance [16,17]. Related Work McGhin et al [18] provide an overview of the main opportunities and challenges for blockchain in the health care field and describe some initiatives (both in academia and industry) focused on developing blockchain solutions. Vazirani et al [19] detailed a systematic review examining the feasibility of blockchain for electronic health record (EHR) systems, finding several trade-offs that need to be considered during the design and development of blockchain. Trade-offs were further explored by O’Donoghue et al [20]. Farouk et al [13] provided a similar review to this one on the use of blockchain in the health care industry but mostly focused on its integration with Internet of Things devices and record management. Hasselgren et al [21] conducted a scoping review of blockchain in health care and, while focusing on peer-reviewed publications rather than the industry, they found that both the number and quality of blockchain research is growing. Chukwu and Garg [22] provide a systematic review of blockchain applications specifically for the use of EHRs and health data sharing and do not focus on industry applications. Agbo et al [23] conducted a systematic review of blockchain applications in health care, also focusing on academic literature, although some studies mention companies working with blockchain. The use cases found in this work are very similar to the use cases explored in this paper (suggesting a convergence between academia and industry research), but Agbo et al [23] found a predominance of studies focusing on EHRs when compared with other areas. Most of these did not have an industry focus; rather, they usually discussed the computer science aspects of the technology or evaluated mostly academic work. In addition, as found by Agbo et al [23], most reviews focused on EHRs and not on additional use cases. Therefore, this review contributes to preview work by providing an overview of blockchain applications in the health care industry, while identifying what challenges and use cases are the current focus of health care companies working with blockchain. JMIR Med Inform 2021 | vol. 9 | iss. 6 | e20713 | p. 2https://medinform.jmir.org/2021/6/e20713 (page number not for citation purposes) Velmovitsky et alJMIR MEDICAL INFORMATICS XSL•FO RenderX http://dx.doi.org/10.2196/20713 http://www.w3.org/Style/XSL http://www.renderx.com/ Methods Overview This narrative review [24] focuses on providing eHealth experts with a comprehensive narrative review of blockchain in health care. Blockchain is a novel technology that can provide increased transparency to data transactions in health care and public health [6,10,11]. Owing to its novelty and early stage implementation, significant development has been accomplished at the industry level, driving this review toward a combination of peer-reviewed academic literature and gray literature. Our aim was to analyze blockchain in health care from an industry perspective, focusing on solutions developed by health and technology companies (although results from research and development initiatives and academia were used to complement knowledge when necessary). Although not a scoping review, this paper followed the framework defined by Levac et al [25] for scoping reviews, ensuring that the findings were analyzed in a systematic manner. This framework consists of six stages: (1) identifying the research question (RQ); (2) identifying relevant studies; (3) selecting studies; (4) charting the data; (5) collating, summarizing, and reporting results; and (6) consultation (optional). In this narrative review, we leveraged phases 1-5. Identifying the RQ The primary objective is to identify how the health care industry views the potential of blockchain to solve current challenges. To fulfill this, two secondary goals need to be achieved: we must understand how blockchain works and the challenges facing the industry. Therefore, the following RQs were used to guide the reviews: 1. How do the blockchain systems work? 2. What are the current challenges faced by the health care industry today that can be addressed by blockchain technology? 3. For each of these challenges, which blockchain solutions are being developed by the health care industry? Identifying Relevant Studies Our review analyzes how the health care industry perceives the blockchain’s potential to solve current challenges. To this end, we looked at gray literature in addition to traditional databases such as IEEE and PubMed, including search and news outlets such as Google Scholar, CoinDesk [26], CoinTelegraph [27], and Medium [28]. The keywords were a combination of “blockchain,” “distributed ledger,” “health,” “industry,” and “health care.” Whenever possible, we looked at technical reports (usually available on companies’ websites) in addition to news articles. Study Selection The primary exclusion criteria involved selecting solutions that address issues or challenges in health care. Blockchain solutions that only had applications in unrelated fields were not included. Additional restrictions included practical concerns regarding availability and language (only English references were included). Charting the Data To extract useful insights from the publications, we focused on two main types of information: • What are the main health care challenges that the solution aims to improve? • How is blockchain being used to improve the challenges? More specifically, we looked at the main objective of the blockchain solution and the methods in which blockchain is being developed. Relevant bibliographical information, including title, authors, country, and year, was also extracted. This review focused on technical reports. If the technical report did not provide sufficient information, web articles were used to complement the results. Collating, Summarizing, and Reporting the Results Following the recommendations presented by Levac et al [25], the steps are as follows: • Analysis: for each solution being presented, we mapped the challenges addressed and how blockchain is being used. • Reporting results: after presenting additional information on blockchain, we will describe the challenge in question and its importance in health care, followed by a discussion on how blockchain is being used by the industry in this context. • Implications for future research, practice, and policy: this final step will be addressed in the Discussion section, where we discuss the limitations of blockchain and additional concerns. Results Overview We started this review by presenting relevant background information about blockchain, followed by an overview of the main challenges identified in our review: EHRs, supply chain, health insurance, genomics, and consent management. For each of these areas, we have also presented blockchain solutions developed by industry. Table 1 provides a summary of the results by describing each of the five identified challenges explaining how blockchain can offer a solution, along with examples. JMIR Med Inform 2021 | vol. 9 | iss. 6 | e20713 | p. 3https://medinform.jmir.org/2021/6/e20713 (page number not for citation purposes) Velmovitsky et alJMIR MEDICAL INFORMATICS XSL•FO RenderX http://www.w3.org/Style/XSL http://www.renderx.com/ Table 1. Results of the literature review. SolutionsDescriptionChallenges Blockchain can provide an overarching framework that allows transparent and auditable access to dis- parate individuals’ health records stored off-chain. Patients would control data sharing parameters and access. Some solutions also discuss integrating health data from less traditional sources (eg, connected de- vices) and the creation of a health data marketplace, in which patients can sell their data to buyers through crypto tokens Electronic health records • MedRec [7,8,29], PatientTruth [30,31], CareX [32,33], MEDIS [34,35], GEM [36-40], MedicalChain [41,42], Humantiv and Medoplex [43-45] Blockchain can establish an immutable record of a product’s tracing throughout the supply chain. In the case of health care, there have been many solutions that implement a blockchain to track-and-trace drugs and food products. In addition, smart contracts can be used as monitoring and alert systems for proper trans- port conditions (eg, a certain temperature range) Supply chain • Drug supply chain: BlockVerify [46-48], Merck [49,50], Modum [51-54] • Food supply chain: IBM Food Trust [55-58], Alibaba and Ant Fi- nancial [59,60] Smart contracts on the blockchain can potentially help to settle health insurance claims and manage payment in real time, making the process more efficient and transparent for payers, providers, and patients. Other potential use cases include pharmaceutical and medical benefits, checks, and payment risk calculation Health insurance • PokitDok and DokChain [61-67], GEM [39], Payspan [68,69] Much like with electronic health records, blockchain can provide a mechanism for controlling access to separate existing data banks of genetic information. In addition, blockchain can directly connect sellers of genomic data-to-data buyers, creating a genomic data marketplace. Data buyers could even provide rewards for individuals to sequence their genomes, creating their own data sets (eg, providing crypto tokens to in- dividuals with a certain feature to be researched, in return for their genomic information) Genomics • Nebula Genomics [9,70], LunaDNA [71-75], Shivom [76-79], Zenome [80,81], EncrypGen [82-85], Macrogen [86-88] Blockchain can provide an immutable and timestamped log of consent, allowing individuals to grant and re- voke consent for different data types and periods. In the case of health studies, it can also help researchers to easily track, manage, and update user consent Consent manage- ment • My31 app [89,90], Bitfury [91,92], HealthVerity Consent [93], Verifiable Audit Trail (tracking of events related to health data) [94-98], INSERMa and APHPb consent project [14], Queen’s Uni- versity BlockTrial [99], Patient Control and Consent Blockchain initiative [100-102], Ubiquitous Health Technology Lab [6,103] aINSERM: Institut National de la Santé Et de la Recherche Médicale. bAPHP: Assistance Publique-Hôpitaux de Paris. What Is Blockchain? Blockchain is a virtual distributed ledger that records transactions among parties. It is operated by a network of computers in which each participant is called a node and possesses a copy of the ledger, regularly updated to ensure consistency. In other words, all nodes have access to the exact information [12,18]. When a user makes a transaction, this transaction is timestamped and sealed in a block [12]. Through a consensus mechanism, this block is linked to previous existing blocks—hence the name blockchain. Different blockchains (eg, Bitcoin and Ethereum) have different consensus mechanisms [12]. A typical consensus mechanism, called Proof of Work, requires the nodes in the network to randomly guess a number that solves a mathematical puzzle; the first node to discover it seals the block. This process is called mining [6,12,13,18]. The linkage between blocks is achieved through a method called hashing, in which new blocks point to the previous ones [12]. This technique converts data into a string of characters, called a hash. For example, a user may convert a text into the following hash: “f1abc234b79f6d6ay42a12c53468a1b13553r1r0fgr4039 rf08h958b5232b9n8.” If a single character from this hash is changed, an entirely new string is generated. Although it is easy to generate a hash from a piece of information, it is impossible to discover the original information from a hash [12,22]. The Bitcoin blockchain hashes the nonce, alongside the transaction information and the hash of the preceding block. If a malicious party tries to tamper with information already stored in a block, the hash is altered, breaking the chain. This ensures that the blocks cannot be tampered with, and the information contained in the blockchain cannot be altered. Therefore, blockchain is a tamperproof digital ledger where all participants have access to an immutable version of the truth [12,18]. The flow of a transaction in the blockchain is shown in Figure 1. JMIR Med Inform 2021 | vol. 9 | iss. 6 | e20713 | p. 4https://medinform.jmir.org/2021/6/e20713 (page number not for citation purposes) Velmovitsky et alJMIR MEDICAL INFORMATICS XSL•FO RenderX http://www.w3.org/Style/XSL http://www.renderx.com/ Figure 1. Flow of a transaction in the blockchain. Blockchain is a type of distributed ledger technology, in which a consistent ledger is shared among parties to store a record, creating a distributed database. It is a distributed ledger technology that uses cryptographic and consensus mechanisms to increase trust [22]. There are also different types of blockchains. Although the nomenclature varies, they are usually defined as follows [13,104,105]: • Public blockchain: all participants can read and write new information to the ledger. Although new information can be added, no information can be deleted. Bitcoin is an example of a public blockchain. • Permission (consortium and federated) blockchain: this is owned by a consortium of participants who define the permissions for joining and updating the network. For example, a consortium blockchain owned by health care providers can allow patients to change their information, but only providers may upload new information. • Private blockchain: this is owned by a single entity that manages access, permission to read or write data, and even data deletion. Among the blockchain communities, some are of the opinion that private blockchains defeat the purpose of decentralized technologies by introducing a central authority. From a health care perspective, one of the biggest concerns in capturing and coding patient information is privacy [106]. Several blockchain implementations allow the creation of smart, codified contracts that allow for the storage of immutable information. For example, Ethereum enabled the creation of smart contracts that codify contract agreements. When several parties agree to a transaction, they create mechanisms to ensure trust [6,12,107]. Smart contracts write the terms of a contract in code, which is executed on the blockchain, and has the ability to be self-executing and self-enforcing [12]. Therefore, smart contracts can minimize trust concerns among parties [12,18,107]. Blockchain’s features and design make it a model for processes plagued by trust issues [6,12,108], and it is ideal for increasing trust in contexts involving parties that do not have reason to trust each other [6,12,108]. One such context is health care [6]. Blockchain in Health Care: Challenges and Solutions The following subsections describe a challenge in health care and discuss blockchain solutions being developed by companies to address them. Electronic Health Records Challenge Description EHRs digitally store patients’ health data [6,7,109,110]. However, data are fragmented throughout EHR systems: patients often interact with different health care providers (usually the stewards of the data), creating challenges related to accessing past information [6,7,22]. In addition, providers have different EHR systems that may not be fully interoperable [6,7]. These factors contribute to difficulties in data sharing [6,7]. Patients’ health data end up in silos and cannot be integrated with data from other providers or sources, such as connected devices. Ultimately, there is no easy way to obtain a holistic view of a patient’s health, leading to errors, delays, and poorer health outcomes [6,7,18,110]. Use of Blockchain Blockchain solutions can create an overarching hub, potentially on the cloud, to link all records of individual patients [7,8,18,29], without storing health data on the blockchain itself [7,8,29,111]. Rather, the blockchain infrastructure would act as a hub that points to the location of a patient’s records off-chain [7,8,29]. Data access and changes to records can be tracked and displayed to the patient in real time. Furthermore, patients could control access to their records by giving permission to providers, researchers, and third parties to access their data. In this manner, an EHR-blockchain solution would allow for all health data from individuals to be accessed and controlled by the patient, facilitating a complete view of patients’ health [7,8,18,29]. This solution would also give patients greater control and transparency over their health data [7,8,12,18,19,29]. For example, MedRec is a blockchain-enabled solution for EHRs [7,8,29]. It is a system developed by the Massachusetts Institute of Technology that provides a transparent view of medical history. MedRec uses smart contracts in Ethereum to encode metadata by referencing medical data from different sources, including information about ownership and permission. These references “create an accessible bread crumb trail for medical histor[ies]” [7]. Providers may append a new patient JMIR Med Inform 2021 | vol. 9 | iss. 6 | e20713 | p. 5https://medinform.jmir.org/2021/6/e20713 (page number not for citation purposes) Velmovitsky et alJMIR MEDICAL INFORMATICS XSL•FO RenderX http://www.w3.org/Style/XSL http://www.renderx.com/ record in MedRec, but patients are the ones who give permission for data to be accessed and shared. This increases transparency and allows patients to keep track of their records [7,8]. Similar solutions include PatientTruth [30,31], CareX [32,33], MEDIS [34,35], and MedicalChain [41,42]. Typically, EHR-blockchain solutions store references to off-chain files containing EHRs and also work with less traditional sources, such as data from connected devices. Patients control their records and with whom they wish to share their data (eg, health care professionals, hospitals, and insurance providers). Some of these solutions allow patients to sell deidentified records (eg, to health studies) with a crypto token from the platform. The financial component creates a form of health data marketplace in which patients own and are able to profit from their health data. Another organization working with blockchain in an EHR context is CitizenHealth [33,43], which developed two solutions: Humantiv [44], which also combines data from EHRs and other sources with an added gamification component in which patients earn rewards according to their health indicators, and Medoplex [45], the company’s marketplace component. GEM, a US-based start-up, is developing a solution that uses Ethereum to create a shared network where providers have real-time access to medical documents [18]. GEM is partnering with Nordic-based Tieto to create a blockchain platform that enables patient control over medical records and genomic data [40,112,113]. It is important to note that a blockchain infrastructure, as described above, could mitigate data sharing issues by providing an interoperable, auditable, and secure landscape of transactions controlled by data owners. This, in turn, would allow easy and transparent access to disparate health records. As stated by McGhin et al [18], when discussing blockchain cloud infrastructures, “the role of blockchain in cloud data infrastructure is facilitating the creation of a decentralized and trusted cloud data provenance architecture that allows tamperproof records, greater transparency of data accountability, and enhanced privacy and availability of the data.” However, the blockchain itself does not impact the interoperability of the health data itself or the local systems in which it is stored. Rather, it acts as an overarching infrastructure with references to off-chain resources whose access is auditable, secure, and transparent to all authorized parties within the distributed network. Drug Supply Chain Challenge Description One of the biggest challenges faced by pharmaceutical companies today is counterfeit drugs. In total, US $200 billion are lost to counterfeit drugs annually, and their use puts patients’ lives at risk [46]. Manufacturers do not have a unified and interoperable system of supply chain management, lack incentives to share data and information, and are consequently siloed, making end-to-end traceability and drug provenance difficult [46,114]. In the United States, the Drug Supply Chain Security Act (DSCSA) established a set of requirements that must be implemented by pharmaceutical companies until 2023. These requirements include product tracing and verification [46,115,116]. Use of Blockchain By storing transactional data from the supply chain on blockchain, it is possible to establish an immutable record of provenance [117]. Blockchain can provide a transparent ledger that traces products throughout the supply chain, from manufacturing to distribution. This will ensure compliance with the DSCSA and improve patient safety. Furthermore, blockchain can also track whether products are being transported and handled under appropriate conditions [111]. One of the companies working in this scenario was BlockVerify. The company is working on a DSCSA-compliant solution that traces products and identifies counterfeit drugs [46-48] A product is labeled with BlockVerify’s tag and verified along the supply chain, with a permanent record on a private blockchain. Consumers and retail locations can use this record to ensure that the product is genuine. Merck has filed a patent to use blockchain to track drug information in …