Cybersecurity for Blockchain-Based IoT Systems: A Review

Abstract

The Internet of Things (IoT) has become a pervasive technology with various applications ranging from smart homes and cities to industrial automation and healthcare. However, the increasing adoption of IoT devices has also raised significant concerns about cybersecurity and privacy. Blockchain, as a distributed and immutable ledger technology, has been proposed as a potential solution to enhance the security and privacy of IoT systems. Blockchain-based IoT systems offer several benefits, such as decentralization, transparency, and data integrity. However, they also pose unique cybersecurity challenges that need to be addressed for their secure and reliable deployment. In this paper, we review the existing literature and highlight the key challenges in cybersecurity for blockchain-based IoT systems. We categorize these challenges into three main areas: (i) IoT device security, (ii) blockchain security, and (iii) integration of IoT devices with blockchain (network security). Through an in-depth analysis, we present the current state of research and discuss potential solutions for each challenge. Additionally, we contribute by identifying future research directions to address these challenges and enhance the cybersecurity of blockchain-based IoT systems.

1. Introduction

The Internet of Things (IoT) refers to the network of interconnected devices, sensors, and systems that communicate and exchange data to enable various applications and services [1]. The IoT has gained significant momentum in recent years and is being widely adopted across diverse domains, including smart homes, smart cities, healthcare, transportation, industrial automation, and agriculture, among others [2,3]. However, the rapid proliferation of IoT devices has also raised concerns about their security and privacy [4].

IoT devices are often resource-constrained, with limited computational capabilities and storage capacities, making them vulnerable to security threats, such as unauthorized access, data breaches, tampering, and malware attacks [5,6]. Additionally, the centralized architecture of many IoT systems presents a single point of failure, making them susceptible to systemic risks [7].

Blockchain technology, introduced by Satoshi Nakamoto in 2008 as the underlying technology of Bitcoin, has emerged as a potential solution to enhance the security and privacy of IoT systems [5]. Blockchain is a distributed ledger technology that allows for secure, transparent, and tamper-proof transactions [3]. By leveraging blockchain technology, IoT systems can benefit from enhanced security and privacy [8]. Blockchain offers several advantages that contribute to the security of IoT systems:

• Decentralization: Blockchain is a decentralized technology, which means that it is not controlled by any single entity [9]. This makes it difficult for hackers to target and attack. In a centralized system, all data is stored on a single server, making it a single point of failure. In a decentralized system, data is stored on multiple nodes, which makes it more difficult for hackers to gain access to all of the data.
• Transparency: Blockchain is a transparent technology, which means that all transactions are recorded on the blockchain and are visible to all participants [10]. This makes it difficult for hackers to commit fraud or tamper with data. In a centralized system, transactions are not always transparent, making it difficult to track down fraud or identify those responsible for tampering with data.
• Consensus Mechanisms: Blockchain uses consensus mechanisms to validate transactions. Consensus mechanisms are algorithms that ensure that all participants in the network agree on the validity of a transaction [11]. This makes it difficult for hackers to manipulate the network and approve fraudulent transactions. In a centralized system, a single entity is responsible for validating transactions, making it easier for hackers to manipulate the system.
• Cryptographic Techniques: Blockchain uses cryptographic techniques to secure data. Cryptographic techniques are algorithms that encrypt data and make it unreadable to unauthorized users [12]. This makes it difficult for hackers to steal data from the blockchain. In a centralized system, data is often stored in plain text, making it easier for hackers to steal data.
• Smart Contracts: Blockchain can be used to create smart contracts, which are self-executing contracts stored on the blockchain. Smart contracts are tamper-proof and irreversible, enabling automation and enforcement of agreements between parties [13]. This can improve the efficiency and security of IoT systems.

By incorporating these security features, blockchain-based IoT systems can provide a robust framework for ensuring the integrity, privacy, and reliability of IoT data and transactions. In the context of blockchain-based IoT systems, several layers can be identified to understand their architecture and security aspects [14]. Figure 1 illustrates these layers associated with IoT systems, as follows:

• Device Layer: This layer consists of the IoT devices themselves, such as sensors, actuators, and embedded systems. These devices collect and generate data, which is then transmitted to the blockchain network for processing and storage.
• Communication Layer: The communication layer facilitates the transmission of data between IoT devices and the blockchain network. It encompasses protocols, standards, and network infrastructure that enable secure and reliable communication.
• Blockchain Layer: The blockchain layer is the core component of the system and comprises the distributed ledger and associated consensus mechanisms. It records and validates transactions, ensuring the integrity and immutability of the data stored on the blockchain.
• Smart Contract Layer: This layer involves the implementation of smart contracts, which are self-executing contracts with predefined rules and conditions. Smart contracts enable automation, enforce business logic, and facilitate secure interactions between IoT devices and the blockchain network.
• Application Layer: The application layer includes the various applications and services built on top of the blockchain-based IoT system. These applications leverage the secure and transparent nature of the underlying blockchain to provide functionalities such as data analytics, supply chain management, and decentralized control.

Blockchain-based IoT systems can improve data integrity, transparency, accountability, and interoperability [15]. However, the deployment of blockchain-based IoT systems also presents unique cybersecurity challenges that need to be addressed [16]. These challenges encompass areas such as IoT device security, blockchain security, and the integration of IoT devices with the blockchain infrastructure [17].

Understanding and addressing these challenges are crucial for ensuring the secure and reliable deployment of blockchain-based IoT systems [18]. Continuous research and collaboration among different stakeholders are necessary to overcome these challenges and enable the widespread adoption of blockchain-based IoT systems in various industries [19].

This paper aims to provide a comprehensive review of the existing literature pertaining to cybersecurity challenges in blockchain-based IoT systems. In Section 4, the challenges are categorized into three main categories: (i) IoT device security, (ii) blockchain security, and (iii) integration of IoT devices with blockchain (network security). In Section 5, a detailed analysis is conducted for each challenge, covering the discussion on IoT security and blockchain, and the potential applications of blockchain for IoT in smart cities. Furthermore, existing solutions and their limitations are examined. Section 6 focuses on future research directions, outlining strategies to address these challenges and enhance the cybersecurity of blockchain-based IoT systems. By offering a comprehensive overview and discussing potential solutions, this paper makes a valuable contribution to the existing knowledge in this field.

2. Research Methodology

A systematic literature search was conducted in accordance with the PRISMA guidelines, which is a useful tool to control the flow of the data and goes through three stages [20]. During the identification stage, the Google Scholar, Saudi Digital Library, and ScienceDirect databases were searched using the following search terms: “Blockchain AND IoT AND Security AND (Privacy OR Integrity) AND (Opportunities OR Challenges)”. The search was limited to peer-reviewed articles published between 2016 and 2023. Inclusion criteria were studies that discussed the use of blockchain for IoT security. A total of 26 articles were selected for this literature review. Figure 2 illustrates the PRISMA methodology. The identification stage is where items are identified for review. Through this step, and before screening, 18,421 records have been removed for different reasons such as duplicate records or marked as ineligible by Zotero (an automation tool). The screening stage is where the papers are screened and selected for review. At the screening stage, 747 out of the 951 articles reviewed for title and abstract were rejected for not closely fulfilling the requirements. The eligibility step is where the papers are eligible to be included. The included stage, is where a list of studies to be included in the systematic review will be obtained. In the included stage, 25 articles were selected; 88 articles were rejected for other reasons such as being in a foreign language (such as Russian, Chinese… etc), there was no access to the records, or it was out of the range, leaving 25 articles for review.

3. Literature Survey

In this section, we provide a comprehensive overview of the significant research findings and insights on blockchain security in IoT systems. We discuss the various methodologies, approaches, and frameworks that researchers have employed to investigate the potential benefits, challenges, and applications of blockchain technology in securing IoT devices and networks. Additionally, we highlight the key findings, including the design of architectures, algorithms, and protocols for efficient and secure blockchain-based IoT systems, and the evaluation of performance metrics, such as scalability, privacy, and trust.

Dorri et al. [1] explored the potential benefits of combining blockchain technology with the Internet of Things (IoT), as well as the challenges that arise in this context. The authors started by introducing the concept of IoT and its potential applications in various industries. They then discussed the benefits of integrating blockchain technology into IoT, such as enhanced security, privacy, and transparency. However, the paper also highlighted the challenges that arise when integrating blockchain and IoT. One of the primary challenges discussed in the paper is scalability. IoT devices generate a vast amount of data, and blockchain technology can struggle to handle the scale of this data. The authors discussed various approaches that can be used to address this challenge, such as sharding and off-chain solutions. Another significant challenge discussed in the paper is security. IoT devices can be vulnerable to various types of cyber-attacks, and blockchain technology can help enhance the security of these devices. However, the paper also highlighted the need for secure consensus mechanisms and cryptographic techniques to ensure the security of blockchain and IoT systems. Li et al. [2] provided a comprehensive review of the various security issues that arise in the context of blockchain systems. One of the primary security challenges discussed in the paper is the vulnerability of blockchain systems to double-spending attacks. Double-spending attacks occur when a user spends the same cryptocurrency twice, leading to a loss of trust in the system. The authors discussed various approaches that can be used to mitigate these risks, such as the use of consensus mechanisms and cryptographic techniques. Another significant security challenge discussed in the paper is the risk of 51 percent attacks. A 51% attack occurs when an attacker gains control of 51 percent of the computing power in a blockchain network, allowing them to manipulate the system for their own gain. The authors discussed various techniques that can be used to prevent 51% attacks, such as network partitioning and the use of consensus mechanisms. The paper also discussed the risks and challenges associated with the use of smart contracts in blockchain systems. Smart contracts are self-executing contracts that are programmed to automatically execute when certain conditions are met. However, these contracts are vulnerable to various types of attacks, such as code exploits and denial-of-service attacks. The authors discussed various approaches that can be used to mitigate these risks, such as auditing and testing smart contracts for vulnerabilities. The authors highlighted the need for further research and innovation in this area to ensure the widespread adoption and effectiveness of blockchain technology. The paper also provided a detailed review of the existing security measures and solutions proposed to address these challenges, making it a valuable resource for researchers and practitioners in the field of blockchain security.

Zheng et al. [3] discussed in detail the technical aspects of blockchain technology, explaining how it enables secure and transparent record-keeping without the need for a central authority. They also discussed the various types of consensus mechanisms used in blockchain, such as Proof of Work and Proof of Stake, and how they helped to ensure the integrity of the blockchain. The authors also explored some of the challenges facing blockchain technology, such as scalability and interoperability, and discussed potential solutions to these issues. In terms of future trends, the paper highlighted some of the potential applications of blockchain technology beyond its current use in cryptocurrency. These include applications in fields such as finance, supply chain management, and healthcare, where the ability to securely and transparently track transactions and data could be highly beneficial. The authors also discussed the potential for blockchain to be used in conjunction with other emerging technologies, such as the Internet of Things and artificial intelligence. It is a useful resource for anyone looking to understand the technical aspects of blockchain and its potential applications. Panarello et al. [4] presented a systematic survey of the integration of blockchain and Internet of Things (IoT) technologies. The authors provided an overview of blockchain and IoT, and explained how the two technologies can be integrated to enhance security, privacy, and reliability in IoT systems. The paper covered a wide range of research and development efforts in blockchain–IoT integration, including applications in areas such as supply chain management, healthcare, and energy management. The authors identified key challenges associated with this integration, such as scalability, interoperability, and energy consumption. The paper also presented a taxonomy of blockchain-IoT integration architectures, classifying them according to their level of decentralization, data management, and consensus mechanisms. The authors discussed the advantages and disadvantages of each architecture, and highlighted the need for further research to develop more efficient and scalable solutions.

Dorri et al. [5] explored the potential of using blockchain technology to enhance security and privacy in the context of Internet of Things (IoT) devices. The authors presented a case study of a smart home, where various IoT devices are interconnected and communicate with each other. They highlighted the security and privacy risks associated with such devices, including the potential for unauthorized access and data breaches. The paper proposed the use of blockchain technology as a solution to these issues, allowing for secure and transparent management of IoT devices and their data. The authors described a blockchain-based architecture for the smart home, in which each IoT device has its own identity and can securely communicate with other devices using smart contracts. They highlighted the advantages of this approach, including the ability to control access to devices and data, and to trace the history of transactions. The paper also discussed some of the challenges associated with implementing blockchain for IoT security, such as the need for efficient consensus mechanisms and the potential for increased energy consumption. The authors concluded that blockchain technology has the potential to significantly enhance security and privacy in IoT devices, and that further research is needed to fully explore its capabilities and limitations in this context.

The paper by Islam et al. [6] provided a comprehensive review of the security issues and challenges blockchain technology faces. The authors started by providing an introduction to blockchain and its key features, such as decentralization, immutability, and transparency. Then, they discussed the different types of attacks that blockchain systems may face, such as 51% attacks, double-spending attacks, and smart contract vulnerabilities. They also presented various security measures and techniques that can be used to mitigate these attacks, such as consensus mechanisms, encryption, and multi-signature schemes. The paper concluded with a discussion of some of the remaining challenges in blockchain security, such as scalability, interoperability, and regulatory issues. Raju et al. [7] provided a comprehensive review of cybersecurity issues in the context of blockchain-based IoT systems. The authors highlighted the unique security challenges posed by IoT devices, including their limited computational resources and susceptibility to physical attacks. They also discussed the potential benefits of using blockchain technology to enhance security in IoT systems, such as the ability to create tamper-proof records and control access to devices and data. The paper covered a range of cybersecurity issues in blockchain-based IoT, including attacks on smart contracts, privacy concerns, and the potential for attacks on the blockchain itself. The authors also discussed various security mechanisms that can be used to enhance security in these systems, such as encryption, access control, and intrusion detection. The paper also provided a detailed overview of various blockchain-based IoT applications, such as smart grids, healthcare, and supply chain management, and discussed the specific security challenges and opportunities associated with each application.

Mahmood et al. [8] provided a comprehensive review of the cybersecurity challenges in blockchain technology. The authors identified and analyzed the various cybersecurity issues that arise in the context of blockchain technology, including attacks on smart contracts, privacy risks, and scalability challenges. The paper also discussed the existing solutions and approaches that have been proposed to address these challenges, such as cryptographic techniques and consensus mechanisms. The authors concluded that although blockchain technology offers significant potential for security and privacy, it also presents several significant cybersecurity challenges that must be addressed to ensure its widespread adoption and effectiveness. The survey conducted by Joshi et al. [15] provided a comprehensive overview of the security and privacy challenges associated with blockchain technology. The authors started by discussing the foundational concepts of blockchain technology and its decentralized nature, emphasizing the importance of security and privacy in maintaining the integrity and trustworthiness of the blockchain network. In the study, Le et al. [21] conducted a systematic literature review of blockchain technology to provide a comprehensive understanding of its security properties, applications, and challenges. The study utilized a structured approach to search and evaluate relevant literature from various academic databases. The authors analyzed the selected studies based on their research design, sample size, data sources, and findings. The study found that blockchain technology offers various security properties such as immutability, transparency, and decentralized control, making it an attractive option for various applications such as supply chain management, financial services, and healthcare. However, the review also highlighted several challenges that need to be addressed for the widespread adoption of blockchain technology, such as scalability, interoperability, privacy, and governance. The authors concluded that further research is required to address these challenges and maximize the potential of blockchain technology in various domains. The study of Al-Farsi et al. [22] explored the security of blockchain-based supply chain management systems. The authors identified the key security challenges that arise in such systems, including insider threats, data privacy, and interoperability. They also proposed several potential solutions to address these challenges, such as the use of smart contracts, encryption techniques, and multi-factor authentication. The authors concluded that although blockchain has the potential to enhance supply chain security, it is essential to consider the potential risks and challenges associated with its implementation. Furthermore, the paper provides valuable insights into the security issues and opportunities related to blockchain-based supply chain management systems.

The article “BIoMT: A Blockchain-Enabled Healthcare Architecture for Information Security in the Internet of Medical Things” by Badri et al. [23] is relevant to a related study on blockchain-based solutions for healthcare and the Internet of Things (IoT). The article proposed a novel blockchain-enabled healthcare architecture called BIoMT that addressed the security and privacy challenges associated with the Internet of Medical Things (IoMT). The authors discussed the challenges associated with securing health data in IoMT systems, including data confidentiality, integrity, and availability. They then proposed a blockchain-enabled solution that leverages smart contracts and encryption techniques to secure health data in IoMT systems. The proposed architecture also provides patients with control over their data and allows them to selectively share it with healthcare providers. Furthermore, the article provides a detailed evaluation of the proposed architecture’s performance and scalability. The authors compared the proposed architecture with existing IoMT systems in terms of efficiency, security, and privacy. They also discussed the potential challenges and limitations of the proposed architecture, such as interoperability and regulatory compliance. The article “Towards Blockchain-based Auditable Storage and Sharing of IoT Data” by Shafagh et al. [24] proposed a blockchain-based solution for the secure storage and sharing of Internet of Things (IoT) data. The authors argued that the current approaches for storing and sharing IoT data are centralized and lack transparency, making them vulnerable to security breaches and data tampering. The proposed solution uses blockchain technology to provide an auditable and decentralized storage and sharing mechanism for IoT data. The authors discussed the key features of the proposed solution, including data encryption, smart contracts, and consensus mechanisms. They also provided a detailed evaluation of the proposed system’s performance and scalability, comparing it with existing centralized and decentralized IoT data storage systems. Overall, this article provided valuable insights into the potential of blockchain technology to address the security and privacy challenges associated with IoT data storage and sharing. The proposed solution has the potential to enhance the security and transparency of IoT data, which is crucial for ensuring user trust and improving the reliability of IoT systems.

Yli-Huumo et al. [25] provided a comprehensive review of the current state of research on blockchain technology. The authors conducted a systematic review of academic articles related to blockchain technology published between 2008 and 2015. They analyzed the articles based on various criteria, such as the type of blockchain technology, the application domain, and the research method. The article provided a detailed overview of the evolution of blockchain technology, from its origins as the underlying technology behind Bitcoin to its current use in various industries. The authors also discussed the key features of blockchain technology, such as decentralization, transparency, and immutability, and its potential applications, including financial transactions, supply chain management, and healthcare. Figure 3 provides a visual representation of these technologies and properties.Furthermore, the article identified some of the key challenges and limitations associated with blockchain technology, such as scalability, interoperability, and regulatory compliance. The authors also discussed the potential future directions of research on blockchain technology, such as the integration of artificial intelligence and the development of new consensus mechanisms.

Guo et al. [26] provided a detailed overview of the evolution of blockchain technology, from its origins as the underlying technology behind Bitcoin to its current use in various industries. They also discussed the key features of blockchain technology, such as decentralization, transparency, and immutability. Furthermore, the article presented a comprehensive review of the current state of research on the security of blockchain technology. The authors analyzed the existing literature and identified the key security issues in blockchain-based systems, such as attacks on consensus mechanisms, privacy violations, and data tampering. The article also discussed the various approaches to securing blockchain-based systems, such as encryption, access control, and consensus mechanisms. The authors highlighted the importance of addressing these security issues to ensure the widespread adoption and success of blockchain technology. Lin et al. [27] provided a detailed overview of the key features of blockchain technology, such as decentralization, transparency, and immutability. They also discussed the potential applications of blockchain technology, such as financial transactions, supply chain management, and healthcare. Furthermore, the article presented a comprehensive review of the security issues and challenges associated with blockchain technology. The authors analyzed the existing literature and identified the key security issues in blockchain-based systems, such as attacks on consensus mechanisms, privacy violations, and data tampering. The article also discussed the various approaches to securing blockchain-based systems, such as encryption, access control, and consensus mechanisms. The authors highlighted the importance of addressing these security issues to ensure the widespread adoption and success of blockchain technology.

Wylde [28] provided a detailed overview of the key features of blockchain technology, such as decentralization, transparency, and immutability, and its potential applications in various industries. They also discussed the challenges associated with securing blockchain-based systems, such as attacks on consensus mechanisms, privacy violations, and data tampering. Furthermore, the article presented a comprehensive review of the current state of research on cybersecurity and data privacy in blockchain-based systems. The authors analyzed the existing literature and identify the key security issues and challenges in these systems. The article also discussed the various approaches to securing blockchain-based systems, such as encryption, access control, and consensus mechanisms. The authors highlight the importance of addressing these security issues to ensure the widespread adoption and success of blockchain technology. The article “A Taxonomy of Blockchain-Based Systems for Architecture Design” by Xiwei Xu et al. [29] proposed a taxonomy for the design of blockchain-based systems. The authors provided a comprehensive overview of the key features of blockchain technology and its potential applications in various industries. They also discussed the challenges associated with designing blockchain-based systems, such as scalability, interoperability, and security. Furthermore, the article presented a taxonomy for the design of blockchain-based systems, which includes four categories: blockchain infrastructure, blockchain application platform, blockchain-enabled applications, and blockchain service providers. The taxonomy provided a structured approach to designing blockchain-based systems and helped to identify the key considerations for each category. The article also discussed the various approaches to designing blockchain-based systems, such as the use of smart contracts, consensus mechanisms, and data encryption. The authors highlighted the importance of considering these design choices to ensure the successful implementation and adoption of blockchain technology.

Yijun Zou et al. [30] provided a detailed overview of the key features of blockchain technology, such as decentralization, transparency, and immutability. They also discussed the potential applications of blockchain technology, such as financial transactions, supply chain management, and healthcare. Furthermore, the article presented a comprehensive review of the current state of research on blockchain technology in various academic fields, such as computer science, economics, and law. The authors analyzed the existing literature and identify the key trends and future research directions in each field. The article also discussed the various applications of blockchain technology in different industries, such as finance, healthcare, and energy. The authors provided a detailed analysis of the challenges associated with implementing blockchain-based systems in each industry and highlighted the potential benefits of doing so. Casino et al. [31] provided a comprehensive systematic literature review of blockchain-based applications. The authors reviewed a total of 298 papers published between 2008 and 2018 in different academic databases, and classify them based on various criteria, such as application domain, blockchain type, consensus mechanism, and scalability issues. The paper identified five main categories of blockchain-based applications: (i) financial applications, (ii) supply chain management applications, (iii) social applications, (iv) government and public sector applications, and (v) healthcare applications. The authors also discussed open issues and challenges related to blockchain-based applications, such as scalability, interoperability, security, privacy, and regulatory issues. Overall, the paper provided a comprehensive overview of the current status of blockchain-based applications and identified key research directions for future work.

The paper of Conoscenti et al. [32] provided a systematic literature review of the use of blockchain technology for the Internet of Things (IoT). The authors discussed the challenges of the IoT in terms of security, privacy, and reliability, and explored how blockchain technology can address these challenges. They identified several potential applications of blockchain in IoT, including device registration and identification, secure data sharing, and access control. The paper also discussed the characteristics of blockchain that make it suitable for IoT, such as its decentralized nature, immutability, and transparency. The authors analyzed existing research on blockchain and IoT, including academic papers, patents, and technical reports, and provided an overview of the current state of the field. They identified several research gaps and open research questions, such as the scalability of blockchain for IoT and the integration of blockchain with other emerging technologies. However, the paper provided a comprehensive review of the potential benefits and challenges of using blockchain technology for IoT, and highlighted the need for further research in this area. In the study of Kumar et al. [33], they focused on exploring the use of blockchain technology to address security issues and challenges in the context of the Internet of Things (IoT). The authors discussed the need for security in IoT and highlighted the potential benefits of using blockchain technology to address security challenges such as privacy, data integrity, and trust. They also presented a review of different blockchain-based solutions for IoT security issues and discussed their advantages and limitations. The paper concluded that blockchain technology has the potential to provide a secure and trustworthy environment for IoT devices and applications, but more research is needed to overcome challenges related to scalability, interoperability, and energy efficiency.

Alam [34] provided a comprehensive review of the integration of blockchain technology with the Internet of Things (IoT). The paper started with an overview of blockchain technology and its potential to address the limitations of traditional IoT systems. Alam highlighted how blockchain enhances security, privacy, data integrity, and interoperability in IoT networks. Current trends in the adoption and implementation of blockchain in IoT systems are discussed. This includes the emergence of decentralized IoT platforms, smart contracts, and the integration of blockchain with edge computing and artificial intelligence. The paper presented a range of real-world applications where blockchain is applied in the IoT domain. These included supply chain management, smart cities, healthcare, energy management, agriculture, and transportation. The author explored how blockchain improves transparency, traceability, and efficiency in these sectors. Alam emphasizes the significance of security and privacy in blockchain-based IoT systems. The paper explored cryptographic techniques, decentralized identity management, and access control mechanisms to protect sensitive IoT data and ensure secure interactions. Interoperability and scalability challenges in blockchain-based IoT systems are addressed. The paper discussed approaches to integrating blockchain networks with IoT devices and strategies to enhance scalability. The paper concluded by highlighting future challenges and research directions in the field. Areas such as energy consumption, consensus mechanisms, standardization, regulatory frameworks, and user adoption were identified as crucial areas for further exploration.

Khan et al. [35] provided a comprehensive review of the security challenges facing the Internet of Things (IoT), including issues related to confidentiality, integrity, availability, and privacy. The authors discussed various security solutions proposed for the IoT, including encryption, authentication, access control, and intrusion detection. They also highlighted the limitations of these solutions and argued that blockchain technology can provide a promising approach to address IoT security challenges. The article provided an overview of the key features of blockchain technology and its potential applications in the IoT context, such as secure data sharing, trust management, and decentralized control. The authors also identified some open challenges and research directions in the area of IoT security and blockchain, such as scalability, interoperability, and regulatory compliance. Overall, this article provided valuable insights into the current state of IoT security and the potential of blockchain technology to enhance it. Dwivedi et al. [36] proposed a “decentralized privacy-preserving healthcare blockchain for IoT”, which uses a combination of symmetric and asymmetric encryption techniques, as well as smart contracts, to ensure data privacy and security. They also explained how the system incorporates a consensus mechanism to ensure the integrity of the data stored on the blockchain. Furthermore, the article provided a detailed evaluation of the proposed system’s performance and scalability. The authors compared the proposed system with existing centralized and decentralized healthcare systems in terms of efficiency, security, and privacy. They also discussd the potential challenges and limitations of the proposed system, such as interoperability and regulatory compliance. Overall, this article presented a novel approach to addressing the security and privacy challenges associated with these systems, and provided a detailed analysis of the proposed system’s features, performance, and scalability. The article highlighted the potential of blockchain technology to improve the security and privacy of health data in IoT systems and provided valuable insights into the design and implementation of blockchain-based healthcare systems.

Several related works have been examined in the literature, focusing on various categories, challenges, and proposed solutions.

Table 1. Summary of Related Works.

Ref.	Category	Challenge	Proposed Solution
[2]	Blockchain security	Privacy leaks due to public transactions and addresses. 51% attacks and selfish mining attacks. Smart contract vulnerabilities. Double-spending attacks. Sybil attacks. Denial of service attacks.	Use cryptography for transaction and data privacy. Consensus algorithms were resistant to 51% and selfish mining attacks. Detecting and preventing double-spending. Formal verification and static/dynamic analysis for smart contract security. Identity management and Sybil detection methods. Byzantine fault tolerance and mining prioritization against DoS attacks.
[3]	Blockchain architecture	Blockchain architecture, consensus, and future trends.	Consensus algorithms, architecture, and future trends in blockchain.
[4]	Blockchain and IoT integration	Limited resources of IoT devices and privacy and security concerns	Lightweight consensus, clustering, offloading computations, access control, authentication, and encryption.
[5]	Blockchain and Internet of Things (IoT)	Privacy and security concerns due to resource constraints of IoT devices. Most IoT devices have limited computing power, memory, and energy resources, which makes it difficult for them to implement complex cryptographic algorithms for achieving security and privacy in blockchains.	Employ cryptographic techniques, access control, and authentication for security. Utilize anonymous credentials and encrypted data storage to enhance privacy. Use lighter-weight cryptographic techniques that are suitable for IoT devices, as well as implementing access control and authentication mechanisms. It also recommends anonymous credentials and encrypted storage to enhance privacy in IoT blockchains.
[6]	Blockchain security	Double spending, 51% attacks, privacy leaks, man-in-the-middle attacks, and consensus attacks.	Various solutions based on consensus algorithms, encryption methods, access control, and identity management.
[7]	Blockchain-based IoT	Security issues in integrating blockchain and IoT, including Sybil attacks, man-in-the-middle attacks, 51% attacks, double spending, smart contract vulnerabilities, and privacy leaks.	Solutions based on consensus algorithms, cryptography, access control, identity management, blockchain pruning, fog computing, etc.
[8]	Blockchain security	Privacy issues, 51% attacks, smart contract vulnerabilities, lack of transparency and immutability, and insecure mining pools.	Encryption, secure protocols, access control mechanisms and smart contract testing.
[15]	Blockchain security	Privacy issues, 51% attacks, smart contract vulnerabilities.	Consensus algorithms, cryptography, access control, and identity management.
[21]	Blockchain security	Double-spending, privacy leaks, 51% attacks, smart contract vulnerabilities, and lack of scalability.	Various consensus algorithms, privacy-enhancing techniques, access control, and identity management.
[22]	Blockchain-based supply chain management	Privacy and traceability issues, tampering and forgery of data, and man-in-the-middle attacks.	Use techniques like encryption, access control, hashing, and digital signatures to improve supply chain security based on blockchain.
[23,24,36]	Blockchain-based healthcare architecture	Privacy, authentication, access control, and availability.	Cryptography, access control, auditing, and identity management.
[25]	Blockchain-based IoT	Security issues and privacy leaks.	Consensus algorithms, cryptography, access control, and identity management.
[27,28]	Blockchain security	Fifty-one percent attacks, double-spending, privacy leaks, and smart contract vulnerabilities.	Consensus algorithms, cryptography, access control, identity management, and formal verification.
[29]	Blockchain security	Architectural design issues for blockchain-based systems.	The taxonomy evaluates blockchain-based systems based on characteristics such as scalability, performance, security, efficiency, etc.
[30]	Blockchain security	Security vulnerabilities, scalability challenge, and resource waste.	Stronger consensus mechanisms; Sharding, and off-chain transactions; Energy-efficient mining.
[31]	Blockchain security	Scalability, security and privacy, infrastructure, and economic viability.	Various consensus algorithms, privacy-enhancing techniques, virtualization, and optimization methods.
[32]	Blockchain and IoT integration	Security issues related to integrating blockchain and IoT, including privacy, authentication, access control, availability and robustness.	Consensus algorithms, encryption, access control, auditing, and monitoring.
[33]	Blockchain and Internet of Things (IoT)	Privacy issues, tampering of data, availability, scalability, and infrastructure.	Use techniques like encryption, hashing, authentication, access control, and reducing block size to improve IoT security based on blockchain.
[34]	Blockchain and Internet of Things (IoT)	Privacy, tampering of data, availability, scalability, and infrastructure.	Cryptography, hashing, access control, and reducing block size.
[35]	Internet of Things (IoT) security	Security and privacy issues.	Consensus algorithms, cryptography, access control, identity management, and fog computing.

provides a summary of these works, highlighting their key aspects and contributions.

4. Challenges of Using Blockchain for Securing IoT Networks

The literature review reveals several key findings related to the cybersecurity of blockchain-based IoT systems. In this section, we discuss the potential benefits and challenges of using blockchain for securing IoT networks by categorizing these challenges into three main areas:

4.1. IoT Device Security

IoT devices are the foundation of any IoT system and play a critical role in collecting, processing, and transmitting data. However, IoT devices are often vulnerable to security threats due to their resource-constrained nature, lack of security mechanisms, and diverse deployment environments [14]. The following are the key challenges in IoT device security in the context of blockchain-based IoT systems:

4.1.1. Device Authentication and Authorization

Authenticating and authorizing IoT devices is a fundamental security requirement to ensure that only authorized devices can participate in a blockchain-based IoT system. However, traditional authentication methods such as username/password or cryptographic keys may not be suitable for resource-constrained IoT devices due to their limited computational capabilities and storage capacities [24,25]. Ensuring secure device authentication and authorization in a blockchain-based IoT system requires the development of lightweight and scalable methods that can efficiently authenticate and authorize IoT devices while preserving their security and privacy [32].

4.1.2. Device Integrity and Firmware Updates

Ensuring the integrity of IoT devices and their firmware is critical to prevent unauthorized modifications that could compromise the security and privacy of the system [3]. However, IoT devices often lack mechanisms to verify the integrity of their firmware or detect and respond to firmware tampering. Moreover, updating the firmware of IoT devices can be challenging due to their distributed and heterogeneous nature [3]. Blockchain-based solutions can leverage smart contracts and consensus mechanisms to ensure the integrity of IoT devices and facilitate secure and efficient firmware updates [15,23].

4.1.3. Secure Communication and Data Privacy

IoT devices communicate and exchange data with each other and with the blockchain network, which requires secure communication channels and data privacy. However, IoT devices may lack the necessary encryption capabilities or may transmit data in plaintext, making them vulnerable to eavesdropping, data breaches, and unauthorized access. Ensuring secure communication and data privacy in a blockchain-based IoT system requires the development of efficient and lightweight encryption methods that can protect data transmitted between IoT devices and the blockchain network [4,5].

4.1.4. Physical Security

The physical security of IoT devices is often overlooked but plays a crucial role in protecting the confidentiality, integrity, and availability of the system. IoT devices are susceptible to physical attacks, such as theft, tampering, and tamper-evident attacks, which can compromise their security and privacy. Ensuring the physical security of IoT devices in a blockchain-based IoT system requires the development of tamper-evident packaging, physical access controls, and secure device deployment strategies [7].

4.2. Blockchain Security

Blockchain is the underlying technology that provides the decentralized and immutable ledger for recording and validating transactions in a blockchain-based IoT system. However, blockchain itself presents unique cybersecurity challenges that need to be addressed to ensure the security and privacy of the system. The following are the key challenges in blockchain security in the context of blockchain-based IoT systems:

4.2.1. Consensus Mechanisms

Consensus mechanisms are fundamental to the security and integrity of a blockchain-based system, as they determine how transactions are validated and added to the blockchain. However, traditional consensus mechanisms, such as proof-of-work (PoW) or proof-of-stake (PoS), may not be suitable for IoT devices due to their resource-constrained nature. Developing lightweight and energy-efficient consensus mechanisms that can accommodate the limitations of IoT devices while maintaining the security and integrity of the blockchain is a significant challenge [2,3,4,5,6,7].

4.2.2. Scalability and Performance

Blockchain-based systems can generate a large volume of transactions, and the scalability and performance of the blockchain are crucial to ensure timely transaction processing and system efficiency [21]. However, traditional blockchains, such as Bitcoin or Ethereum, may not be scalable enough to handle the high transaction volume generated by IoT devices. Developing scalable and high-performance blockchain solutions that can accommodate the requirements of IoT devices, such as high transaction throughput and low latency, is a challenging task [31,32,33,34].

4.2.3. Privacy and Confidentiality

Privacy and confidentiality are critical considerations in a blockchain-based IoT system, as IoT devices often generate sensitive data that needs to be protected from unauthorized access or exposure [8]. However, traditional blockchains are transparent and publicly readable, which can raise privacy concerns. Ensuring privacy and confidentiality in a blockchain-based IoT system requires the development of privacy-preserving techniques, such as zero-knowledge proofs [1], confidential transactions [3], and secure multi-party computation [5], that can protect the sensitive data generated by IoT devices while maintaining the integrity and transparency of the blockchain [27,29].

4.2.4. Smart Contract Security

Smart contracts are self-executing code that runs on the blockchain and enables automated transactions and interactions in a blockchain-based IoT system. However, smart contracts are susceptible to vulnerabilities, such as coding errors, logic flaws, and security loopholes, that can lead to exploits and compromise the entire system [2]. Ensuring the security of smart contracts in a blockchain-based IoT system requires thorough code audits, vulnerability assessments, and best practices in smart contract development, such as using formal verification and code testing techniques [6,7,8,9,10].

4.2.5. Governance and Consensus among Multiple Parties

In a blockchain-based IoT system, multiple parties, including IoT devices, blockchain nodes, and other stakeholders, need to agree on the rules and decisions of the system. Achieving consensus and governance among multiple parties with different interests, incentives, and decision-making processes can be challenging. Developing effective governance models, consensus algorithms, and decision-making mechanisms that can accommodate the diverse nature of stakeholders in a blockchain-based IoT system is a complex task [21].

4.2.6. Regulatory and Legal Challenges

Blockchain-based IoT systems are subject to various regulatory and legal challenges, including data privacy regulations, intellectual property rights, liability, and compliance requirements. Navigating the complex landscape of regulations and laws related to blockchain and IoT, which may vary across different jurisdictions, can be challenging [23]. Ensuring compliance with relevant regulations and laws, addressing legal challenges, and establishing appropriate legal frameworks for blockchain-based IoT systems are essential for their secure and lawful operation [25,35].

4.3. Network Security

In a blockchain-based IoT system, the network connecting the IoT devices and the blockchain network is critical for ensuring the secure and reliable operation of the system. The following are the key challenges in network security in the context of blockchain-based IoT systems:

4.3.1. Distributed Denial of Service (DDoS) Attacks

DDoS attacks are a significant threat to IoT systems, as they can disrupt the availability and performance of the network by overwhelming it with a flood of traffic. In a blockchain-based IoT system, the distributed nature of the network may amplify the impact of DDoS attacks. Implementing robust DDoS mitigation strategies, such as traffic filtering, rate limiting, and anomaly detection, is crucial to maintain the availability and integrity of the system [2].

4.3.2. Sybil Attacks:

Sybil attacks occur when a malicious entity creates multiple fake identities to gain control or influence over the network. In a blockchain-based IoT system, where IoT devices act as network participants, Sybil attacks can undermine the trust and consensus mechanisms of the system. Implementing identity verification mechanisms and reputation systems can help mitigate the risk of Sybil attacks and ensure the integrity of the network [2,7].

4.3.3. Rogue Device Detection

Detecting and mitigating rogue devices that attempt to disrupt the network or compromise the security of the system is critical in a blockchain-based IoT environment. Blockchain technology can help in identifying and tracking the behavior of IoT devices, enabling the detection of rogue devices. Implementing anomaly detection algorithms and network monitoring techniques can enhance the ability to identify and respond to rogue devices in a timely manner [32,33,34].

4.3.4. Interoperability and Standardization

IoT devices and blockchain networks may come from different manufacturers and follow different standards and protocols, leading to interoperability challenges [3,4]. Achieving seamless integration and interoperability between diverse IoT devices and blockchain networks requires the development of standardized communication protocols, data formats, and application programming interfaces (APIs) [29,31].

As the number of interconnected devices in IoT systems continues to grow, there is an increased likelihood of interactions among these devices over the internet. However, this can give rise to several hurdles, particularly because most IoT systems store their collected data in centralized servers. Consequently, when devices need to access the data, they must interact through a centralized network, with data flow occurring via the central server [7]. This process flow is depicted in Figure 4. Figure 4 shows the difference between the traditional IoT data flow and the IoT data flow with blockchain. In the traditional IoT data flow, data is collected by IoT devices and stored in a centralized server. When devices need to access the data, they must interact through the centralized network. In the IoT data flow with blockchain, data is stored on a distributed ledger. This allows devices to interact with each other directly, without the need for a central server.

5. Discussion

IoT systems face various security threats, including the risk of data breaches, malware attacks, and physical assaults. These vulnerabilities arise from the collecting and storing of sensitive data, such as personal information, location data, and financial details, which, if compromised, can lead to identity theft, fraud, and other malicious activities. In this section, we will discuss the security of IoT and blockchain, and the potential applications of blockchain for IoT in smart cities.

5.1. IoT Security and Blockchain

The poor design and maintenance of IoT devices make them susceptible to malware attacks that can result in data theft, device hijacking, or operational disruptions. Furthermore, IoT devices often being situated in remote or unsecured locations makes them vulnerable to physical attacks, including theft, damage, or operational interference [37,38]. As illustrated in Figure 5, IoT systems are vulnerable to several security threats, including:

• Data breaches: IoT devices often collect and store sensitive data, such as user personal information, location data, and financial data. If these data are compromised, they could be used for identity theft, fraud, or other malicious activities.
• Malware attacks: IoT devices are often poorly designed and maintained, making them vulnerable to malware attacks. Malware could be used to steal data, take control of devices, or disrupt operations.
• Physical attacks: IoT devices are often located in remote or unsecured locations, making them vulnerable to physical attacks. Attackers could steal or damage devices, or disrupt their operations.

Blockchain technology offers multiple avenues to bolster the security of IoT systems. Firstly, through encryption, blockchain can safeguard the data stored on IoT devices by rendering it indecipherable to unauthorized individuals. Moreover, blockchain enables authentication mechanisms that verify the identities of users and devices, guaranteeing that only authorized entities gain access to the system. Access control is another vital aspect facilitated by blockchain, permitting precise control over data and device accessibility, thereby limiting potential risks [17,38]. Additionally, blockchain’s vulnerability management capabilities aid in identifying and addressing vulnerabilities within IoT systems, reducing their susceptibility to attacks. Furthermore, incorporating explainable artificial intelligence (XAI) techniques within blockchain-based IoT systems can provide additional benefits [39]. Based on our analysis, we find that blockchain technology can be used to improve the security of IoT systems in a number of ways:

• Encryption: Blockchain can be used to encrypt data stored on IoT devices, making it more difficult for unauthorized users to access.
• Authentication: Blockchain can be used to authenticate users and devices, ensuring that only authorized users have access to the system.
• Access control: Blockchain can be used to control who has access to data and devices, and what they can do with it.
• Vulnerability management: Blockchain can be used to identify and mitigate vulnerabilities in IoT systems, making them less susceptible to attack.
• XAI: XAI techniques aim to explain the inner workings, decisions, and outcomes of complex AI systems in an interpretable and transparent manner. This is particularly valuable for blockchain-based IoT systems due to several reasons [40]:

  –

  Enhancing accountability: By understanding how blockchain decisions are made, stakeholders can ensure the system is functioning correctly and accountable for its actions. This builds user trust.

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  Debugging issues: Interpretable explanations of the blockchain’s behavior can help debug any issues within the system and identify potential vulnerabilities.

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  Adapting to changes: Explanations provide insight into how the system is performing, which can guide necessary changes and updates over time.

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  Deterring attacks: Increased transparency into the blockchain network’s operations can act as a deterrent against potential attackers by making exploitation more difficult.

Furthermore, we review some XAI techniques that could be applied to blockchain-based IoT systems [41,42] including:

• Model summarization: This technique condenses complex models into simpler, interpretable representations. This can be done by using natural language descriptions, decision trees, or other techniques.
• Feature attribution: This technique assigns “importance scores” to features to indicate their relative impact on outcomes. This can be done by using techniques such as sensitivity analysis or local interpretable model-agnostic explanations (LIME).
• Counterfactual explanations: This technique indicates how outcomes would change under different conditions. This can be done by using techniques such as counterfactual regret minimization or counterfactual explanations.
• Causal modeling: This technique uses causal graphs to represent causal relationships within the system. This can be done by using techniques such as structural causal models or Bayesian networks.

By incorporating XAI techniques, blockchain networks can become more transparent and accountable, building trust in IoT systems while also improving their security and adaptability over time. However, it’s important to note that the adoption of XAI in blockchain systems still faces some challenges that need to be addressed [40]:

• Lack of standardization: There is currently no standard for XAI, which can make it difficult to compare and evaluate different XAI techniques.
• Data privacy: XAI often requires access to sensitive data, which can raise privacy concerns.
• Computational complexity: XAI can be computationally expensive, which can limit its scalability.

Despite these challenges, the potential benefits of XAI in enhancing the security, efficiency, and user experience of blockchain systems make it an area worth exploring further.

Table 2. Security challenges and solutions for each layer of the IoT system.

Layer	Security Challenges	Security Solutions
Device Layer	Weak authentication and authorization Outdated firmware Physical tampering	Strong authentication mechanisms Regular firmware updates Physical security measures
Communication Layer	Insecure communication protocols Man-in-the-middle attacks Denial-of-Service (DoS) attacks	Encryption and secure communication protocols Use of digital certificates and secure channels DoS attack prevention and detection mechanisms
Blockchain Layer	51% attack Smart contract vulnerabilities Privacy risks	Consensus mechanisms to prevent 51% attacks Code audits and security testing for smart contracts Privacy-preserving techniques and encryption
Smart Contract Layer	Smart contract bugs and vulnerabilities Lack of legal enforceability	Thorough code review and testing Use of established coding standards Legal frameworks and dispute resolution mechanisms
Application Layer	Insecure application interfaces Data privacy breaches Social engineering attacks	Secure coding practices and input validation Encryption and access control for sensitive data User awareness and education against social engineering

is provided to summarize the security challenges and solutions for each layer of the IoT system [43]. The device layer focuses on authentication, firmware updates, and physical security. The communication layer addresses secure protocols, man-in-the-middle attacks, and DoS prevention. The blockchain layer tackles 51% of attacks, smart contract vulnerabilities, and privacy risks. The smart contract layer emphasizes code review, legal enforceability, and dispute resolution. Finally, the application layer considers secure interfaces, data privacy, and user awareness against social engineering attacks.

In summary, by leveraging the security features offered by blockchain technology, IoT systems can enhance their resilience against security threats, protect sensitive data, and ensure the integrity and reliability of their operations.

5.2. Blockchain for IoT: Potential Applications for Smart Cities

Blockchain technology offers significant potential for enhancing the security and functionality of IoT systems, and it has various applications in domains such as smart cities. By leveraging the decentralized and immutable nature of blockchain, IoT systems can benefit from increased trust, transparency, and efficiency [44]. Here are some key areas where blockchain can be applied in IoT systems, including smart cities:

5.2.1. Data Integrity and Security

One of the primary concerns in IoT systems is the integrity and security of the data collected and transmitted by connected devices. Blockchain can provide a tamper-resistant and auditable ledger for recording and verifying data transactions [45]. By storing data in a decentralized manner across multiple nodes, blockchain ensures that data cannot be easily altered or manipulated. This feature is particularly crucial in smart cities where large volumes of data are generated from various sensors and devices [46]. Blockchain-based data integrity can help prevent data tampering, ensure the authenticity of information, and maintain data privacy.

5.2.2. Identity and Access Management

In IoT systems, ensuring secure and authorized access to devices and services is essential. Blockchain can serve as a decentralized identity management system, where each device or entity is assigned a unique cryptographic identity. These identities can be stored on the blockchain, enabling secure and verifiable authentication and access control mechanisms [47,48]. By utilizing blockchain for identity management, smart cities can establish a trustworthy framework for managing the identities of devices, users, and other entities participating in the IoT ecosystem.

5.2.3. Smart Contracts and Automation

Smart contracts, which are self-executing contracts with predefined rules and conditions, can be deployed on a blockchain to automate interactions and transactions between IoT devices and systems. In the context of smart cities, smart contracts can facilitate various processes, such as energy trading, parking management, waste management, and more. For example, in an energy trading scenario, IoT devices can autonomously negotiate and execute transactions based on predefined conditions stored in smart contracts [49]. By leveraging blockchain-based smart contracts, smart cities can achieve greater efficiency, transparency, and accuracy in their operations.

5.2.4. Supply Chain Management

Blockchain can revolutionize supply chain management in IoT systems by providing end-to-end transparency and traceability. In a smart city context, blockchain can be used to track and verify the movement of goods, monitor environmental conditions during transportation, and ensure the authenticity and quality of products [50]. By storing supply chain data on a distributed ledger, stakeholders can have real-time visibility into the entire supply chain, mitigating risks, reducing fraud, and improving accountability.

5.2.5. Decentralized Infrastructure and Connectivity

In traditional IoT systems, centralized infrastructure and communication networks can be vulnerable to single points of failure or cyber attacks. Blockchain technology can enable decentralized infrastructure and connectivity by leveraging peer-to-peer networks. Devices in a blockchain-based IoT system can communicate directly with each other, eliminating the need for intermediaries and enhancing the system’s resilience [51,52]. This decentralized architecture improves the overall reliability, security, and efficiency of IoT systems, making them more suitable for smart city applications.

5.2.6. Microtransactions and Tokenization

Blockchain-based IoT systems can enable micropayments and value exchange between devices and entities. By leveraging cryptocurrencies or tokens, IoT devices can autonomously exchange value or services based on predefined conditions [53,54,55]. For example, a smart parking system in a smart city can utilize blockchain and tokens to facilitate automated payments for parking spaces based on real-time availability and demand. This tokenization of IoT interactions can simplify and streamline payment processes while reducing transaction costs.

The combination of blockchain and IoT has the potential to revolutionize various aspects of urban living, including transportation, energy management, waste management, public safety, and more [56]. However, it’s important to consider the scalability, interoperability, and governance challenges associated with integrating blockchain into large-scale IoT deployments.

6. Open Issues and Future Directions

Blockchain technology holds great promise for securing IoT networks. However, there are several research limitations that need to be addressed to fully realize this potential. In this section, we discuss some of the most significant challenges and propose future research directions to enhance the cybersecurity of blockchain-based IoT systems.

Table 3. Blockchain limitations and possible solutions.

Technique	Limitations	Possible Solution
Public key identification	Could potentially compromise the privacy of the data being stored on the blockchain.	Use pseudonymous or anonymous identities on the blockchain.
Single consensus algorithm	Could make the blockchain more vulnerable to attack.	Use multiple consensus algorithms.
A single blockchain for all IoT devices	Could make it difficult to scale the blockchain to a large number of users.	Use multiple blockchains for different types of IoT devices.
Proof-of-work consensus algorithm	Could make it difficult to process transactions quickly.	Use a more efficient consensus algorithm.
Blockchain standards	Blockchains are still in their early stages of development, so there is a risk of security vulnerabilities.	Work to develop standards for blockchain interoperability.
Blockchain complexity	Blockchains are a complex technology, so there is a risk that they will be difficult to use for some applications.	Develop user-friendly interfaces for blockchains.

provides a summary of these limitations and potential solutions based on the challenges outlined in Section 4 and our observations and discussions in Section 5.

Table 4. Challenges and future research directions for integrating blockchain and XAI in IoT systems.

Benefits of Integrating Blockchain and XAI in IoT Systems	Challenges	Future Research Directions
Enhanced transparency	Computational and storage requirements	Explore XAI techniques specifically tailored for blockchain-based IoT systems
Trust and accountability	Complexity and interpretability	Develop mechanisms for interpretability and explainability in decentralized settings
Compliance and regulation	Privacy and data protection	Investigate privacy-preserving techniques for blockchain and XAI integration
-	Scalability and performance	Address scalability challenges in consensus mechanisms and AI algorithm performance

highlights the benefits of combining blockchain and XAI, such as enhanced transparency, trust, accountability, compliance, and regulation in IoT systems. Each benefit is associated with specific challenges that need to be addressed, including computational and storage requirements, complexity and interpretability, privacy and data protection, and scalability and performance. The table also suggests future research directions to overcome these challenges and improve the cybersecurity of blockchain-based IoT systems.

In addition to the limitations and challenges discussed above, there are several future research directions that can further improve the cybersecurity of blockchain-based IoT systems:

(A) Scalability: One of the main challenges of using blockchain for IoT security is scalability. Current blockchain systems have limited processing capabilities, which may not be sufficient to handle the vast amount of data generated by IoT devices. Therefore, there is a need for research to develop scalable blockchain systems that can handle the increasing number of IoT devices and the vast amount of data they generate.

(B) Interoperability: Another challenge of using blockchain for IoT security is interoperability. IoT devices use various protocols and standards, which may not be compatible with blockchain systems. Therefore, there is a need for research to develop interoperable blockchain systems that can work seamlessly with different IoT devices and protocols.

(C) Energy Efficiency: The energy consumption of blockchain systems is another challenge that needs to be addressed, especially for IoT networks, where energy-efficient devices are critical. Research is needed to develop energy-efficient blockchain systems that can reduce the energy consumption of IoT devices.

(D) Privacy: Although blockchain provides a secure and transparent system for data storage, it may compromise privacy in some cases. For example, blockchain transactions are recorded permanently, which may not be desirable for some IoT applications that require privacy. Therefore, research is needed to develop privacy-preserving blockchain systems that can protect the privacy of IoT data.

(E) Standardization: The lack of standardization in blockchain and IoT is another challenge that needs to be addressed. The absence of standards may hinder the adoption of blockchain for IoT security. Therefore, there is a need for research to develop standardization frameworks that can facilitate the integration of blockchain with IoT.

7. Conclusions

In conclusion, blockchain-based IoT systems hold immense promise but require concerted efforts to address the associated cybersecurity challenges. By adopting a comprehensive and multidisciplinary approach, which encompasses technical advancements, operational best practices, and regulatory frameworks, we can pave the way for secure and reliable blockchain-based IoT systems that drive innovation and transform industries.

Our research has highlighted critical areas that demand cybersecurity measures in blockchain-based IoT systems, including device security, blockchain security, and network security. Each of these areas presents unique challenges that necessitate specialized solutions. Device security requires the development of lightweight and scalable methods to authenticate and authorize devices, protect data privacy, ensure firmware integrity, and enhance physical security. Blockchain security entails addressing challenges such as consensus mechanisms, scalability, privacy, smart contract security, governance, and regulatory compliance. Network security considerations involve secure connectivity, efficient access control, robust intrusion detection systems, and resilient network infrastructure.

Furthermore, integrating explainable artificial intelligence (XAI) techniques with blockchain technology can enhance transparency and accountability in IoT systems. XAI methods offer insights into AI algorithm decision-making, making them more understandable and interpretable. The integration of XAI with blockchain enables traceability and auditability of AI algorithm steps, particularly vital in domains like healthcare to build trust and ensure compliance with regulations. Further research should explore synergies between blockchain and XAI, effectively integrating them to enhance the security and transparency of IoT systems.

To drive progress in this field, future research should focus on developing blockchain systems explicitly tailored for IoT security. Key areas of focus include scalability, interoperability, energy efficiency, privacy preservation, and standardization. Collaboration among researchers, industry experts, and regulatory bodies is paramount to advancing cybersecurity measures and facilitating the widespread adoption of blockchain-based IoT systems across industries. By emphasizing potential areas for further research, this paper aims to contribute toward strengthening the cybersecurity of blockchain-based IoT systems. Through continuous research, development, and collaboration, we can address the existing challenges and unlock the transformative potential of secure and reliable blockchain-based IoT systems.