# Cybersecurity for Blockchain-Based IoT Systems: A 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. [PERSON] 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. [PERSON] 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  
Figure 2: Selection of Papers for Literature Review using PRISMA. 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. [PERSON] 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.