# Internet of Things and Blockchain Integration: Security, Privacy, Technical, and Design Challenges
###### Abstract  
The Internet of things model enables a world in which all of our everyday devices can be integrated and communicate with each other and their surroundings to gather and share data and simplify task implementation. Such an Internet of things environment would require seamless authentication, data protection, stability, attack resistance, ease of deployment, and self-maintenance, among other things. Blockchain, a technology that was born with the cryptocurrency Bitcoin, may fulfill Internet of things requirements. However, due to the characteristics of both Internet of things devices and Blockchain technology, integrating Blockchain and the Internet of things can cause several challenges. Despite a large number of papers that have been published in the field of Blockchain and the Internet of things, the problems of this combination remain unclear and scattered. Accordingly, this paper aims to provide a comprehensive survey of the challenges related to Blockchain-Internet of things integration by evaluating the related peer-reviewed literature. The paper also discusses some of the recommendations for reducing the effects of these challenges. Moreover, the paper discusses some of the unsolved concerns that must be addressed before the next generation of integrated Blockchain-Internet of things applications can be deployed. Lastly, future trends in the context of Blockchain-Internet of things integration are discussed. BC; BloT; challenge; integration; trend +
Footnote †: journal: _Future Internet_  
0000-0001-999-4000-0001-9999-4000]X.X. (4) the central architecture is no longer robust enough to handle vast amounts of data and end-to-end interactions as a result of the rapid growth of IoT applications. Furthermore, due to the variety of smart devices on the market, maintaining and updating these devices are almost impossible; (5) since transparency is critical for promoting security and trust when designing next-generation IoT solutions, open-source techniques should be considered; (6) because most safe cryptographic methods need a large amount of processing power and energy, the encryption process is a big barrier due to the heterogeneity and limited compute capacity of IoT devices; (7) due to the constantly increasing number of IoT devices number, relevant IoT ecosystems must accommodate future network development while also processing a huge volume of data exchanged in a high-performance manner. The abovementioned challenges cannot be achieved in centralized IoT-cloud architecture. These problems necessitate a rethinking of the IoT's structure. Although decentralized systems for enormous peer-to-peer (P2P) wireless sensor networks have been developed in the past to overcome the drawbacks of the centralized IoT-cloud architecture, security and privacy requirements were lacking until the advent of Blockchain (BC) technology [13]. BC can carry out, organize, and monitor transactions provided by several devices without the need for a centralized cloud. To validate a transaction, BC is a decentralized system that does not require trust among participants. Its origins can be traced back to the cryptocurrency Bitcoin system [14]. The integration of BC and IoT (BIoT) may result in several benefits [15; 16; 17; 18] for IoT security. Firstly, it provides a P2P framework that does not require a middle layer such as a third trusted party. Secondly, BC technology has no single point of failure, and, when it is used with smart contracts, it enables more secure transactions, which protects against various scams since smart contracts provide access control and improve stability, confidentiality, and authentication. By ensuring the data are cryptographically encrypted and signed by the rightful sender, BC ensures data confidentiality and authentication. Thirdly, the capacity of the entire network can be expanded due to its P2P nature. Fourthly, BC enables transactions to be performed quickly.