Table 1.

Challenges with blockchain adoption and core priorities in deploying secure blockchain-based EHR systems

Challenges	Bugs in the security system	Core priorities in deploying secure blockchain	References
Security	Malicious software can use security flaws to create decentralized applications based on the built blockchain. These malicious attacks take advantage of security flaws in smart contract implementation to aid other crimes like identity theft and data theft.	Three goals must fulfill in terms of the following: 1. Confidentiality: Only authorized users have access to the information. 2. Integrity: data must be correct when in transit and must not be tampered with by an illegitimate group. 3. Availability: Access to information and services for legal users is not unfairly withheld.	(Liang et al. 2018)
Privacy	The main challenge in protecting patient data privacy is to present a framework for data privacy and integrity on a blockchain-based EHR that leverages cryptographic methods. This feature makes it impossible to identify a specific patient based on his current account number. In any similar system should rectify the flaws in the protection of patient data. For starters, patients should easily exchange their data because employing blockchain-based frameworks within EHR demands a lot of computer power and takes a long time to finish each task. Second, adding a new node to the blockchain network, which new patients require, necessitates a series of measures to ensure that the patient is trustworthy.	The following requirements must be met for public blockchain privacy protection in healthcare applications: (1). Links among transactions should not be accessible or visible. (2). The information of transaction patterns should be revealed only to their participants. However, a healthcare application built on a private or consortium blockchain can set up an access control policy to meet the data security requirements. (3). The privacy protection of transactions in a public blockchain setting is a “double-edged sword.” A well-behaved patient, on the one hand, wants to keep his identity and actions confidential. (4). On the other hand, an opposing party may use the privacy protection mechanism to conduct an illicit transaction. From the standpoints of legal traceability and accountability, the security of blockchain transactions in healthcare applications could be constrained so that the authority is trustworthy. (5). Researchers should look into how to monitor a particular user and collect all of the messages he has sent out while keeping the user’s critical information private. (6). One potential research problem is to improve privacy in a blockchain with untrustworthy ambient assumptions and low processing costs from a development standpoint. (7). Secure multiparty computation is a potential approach for allowing an untrusted third party to do calculations on patient data without infringing on their privacy.	(Liang et al. 2018)
Scalability	Lack of scalability is another challenge and higher overhead or computational resources in IoMT devices. As a result of this challenge, the blockchain infrastructure’s total processing requirements may be increased. When a large number of smart devices or sensors are present, the problem becomes even more challenging because these devices’ computing capabilities are less than that of a typical computer. The IoT devices in the blockchain network are computationally demanding and include a large overhead bandwidth, resulting in data delays and significant processing power. Such devices may lack the computing capacity required to employ blockchain features, forcing them to function at suboptimal or potentially exorbitant speeds, prohibiting them from simultaneously running their original and blockchain software.	As medical data grows, research is being done on the scalability of blockchain in healthcare applications.	(Al et al. 2019)
Interoperability	The capacity to transmit, analyze, and deal with the allocation across different blockchain networks without the use of an intermediary or central authority is referred to as blockchain interoperability. Because of the absence of interoperability, mass adoption may be nearly impossible. Existing EHR solutions rely on centralized local databases and offline architecture, whereas blockchain technology is decentralized and cloud-based. Moving healthcare systems in this direction and integrating blockchain technology will necessitate the development of an effective EHR system capable of fostering collaboration and interoperability across medical and scientific communities.	Researchers have seen an increase in interoperability efforts to bridge the gap between different blockchains. Many of them try to link private networks to public blockchains or vice versa. Prior approaches that concentrated on public blockchains and cryptocurrency-related tools were less valuable to corporate executives in the long run.	(Al et al. 2019 & Wang and Song 2018)
Anonymity	As public ledgers, Bitcoin blockchain and Ethereum require transactions to be visible by default.	The Ethereum network provides pseudo-anonymity; transactions, for example, are connected to addresses that correspond to public keys derived from user-held private keys, rather than usernames or passwords. Public Ethereum, also known as zk-SNARKS (zero-knowledge succinct non-interactive argument of knowledge), is a cryptographic proof mechanism that allows a user to verify a transaction without exposing the transaction’s underlying data or engaging with the user who broadcast it. In the context of a blockchain, zk-SNARKs allow users to keep their transactions private while still verifying them according to the consensus process of the network. Once implemented, businesses will be able to transact in total anonymity on the same network as their competitors while benefiting from the security of the public Ethereum blockchain.	(Liang et al. 2018)
Latency	Blockchain technology will take time to gain consensus and confirm transactions, which could be an issue when integrating blockchains into healthcare applications that require real-time responses to events and data. A blockchain takes time to process transactions, which is known as transaction latency. The bitcoin blockchain, for example, has a delay of 10 min to confirm each transaction in the network. Although five or six blocks must be added to the chain before confirmation, it is recommended that each transaction be confirmed within 1 h. On the other hand, most traditional database systems only take a few seconds to confirm a transaction.	Lower latency has been linked to blockchain-based IoT devices, but they can be applied to other blockchain applications. The IoT network, which has a large number of devices communicating with each other at the same time, necessitates a network with latency. The consensus method confirms each block’s transaction, which significantly reduces latency affecting the application’s overall performance.	(Badr et al. 2018)