## 2 Overview
### Challenges of Integrating Blockchain Technology and IoT  
Although blockchain technology can provide IoT with effective and efficient solutions, there are many challenges related to various aspects of integrating these technologies together. These include integration challenges with security-related system components, anonymity and data privacy, smart contracts, storage capacity and scalability, resource utilization, predictability, and legal issues. Predictability is crucial in IoT because devices must be able to communicate with their surroundings in real time, which implies that the amount of time it takes for things to interact and the amount of latency between devices must be limited. Many consensus algorithms, such as PoW and PoS, are probabilistic when finalizing a transaction in the blockchain. At the same time, the confirmation confidence of the transaction in confusion is also probabilistic. Including predictability concerns in the blockchain, the design remains a key challenge. Predictability is essential for IoT-based healthcare applications [86]. For both manufacturers and service providers, the blockchain presents a severe issue because it connects individuals from diverse locations without any legal or compliance code to follow. Problems arise when private keys are retrieved or reset and transactions are reversed because there is a lack of rules on how to behave in such situations. It is unclear whether a worldwide, unique blockchain for IoT devices is intended to be governed by manufacturers or open to users in some IoT applications. Legal regulations are a crucial part when integrating blockchain with any other technology [87]. High heterogeneity and the lack of performance of IoT devices caused security issues at multiple levels. In addition, wireless communication and mobility are an additional set of properties that require security. More secure IoT design is even more essential due to the severe consequences caused by the growing number of attacks on IoT networks. Blockchain is widely viewed as a crucial technology for improving the security of IoT. However, the major barrier in integrating blockchain with IoT is the reliability of IoT devices' data, because when the content of data is changed or damaged before it arrives on the blockchain, it will be stored as it is in the chain. Thus, blockchain is unable to identify and verify the integrity of data. Although data can be corrupted by malicious activities, it can be calculated in a wrong manner due to a failure in the devices themselves or any parts of them. Thus, before integrating IoT devices into blockchain technology, they must be properly tested to ensure that they will not cause damage to the system and must be placed in the correct location to prevent physical damage from occurring. Anonymity and data privacy are critical issues for many IoT applications, especially when the device is related to a person, such as in e-health applications. In such applications, anonymity needs to be guaranteed, which is why blockchain is considered an ideal approach. Because data are collected and progress to application and communication levels, it is challenging to deal with data privacy even when many solutions have already been considered. Secure data storage is challenging due to the need for cryptographic software to be integrated into the device, which necessitates careful planning. They must take into account the devices' limited resources and constraints on economic viability when making such enhancements. Because of the restrictions of IoT devices, many security protocols must typically be implemented using less limited devices, such as gateways. In order to accelerate cryptographic operations and reduce the burden on complicated secure software protocols, hardware cryptographic components could be used.