# Internet of Things and Blockchain Integration: Security, Privacy, Technical, and Design Challenges
###### Abstract
Once built and attached to the BC network, each IoT device will get symmetric key pair, eliminating the need for key management and delivery in the BC network. As a consequence, lightweight authentication protocols can be used. The need for computing and memory capacity in IoT devices can be met and organized by these lightweight protocols. Fifthly, the immutability of IoT using data logs stored on BC ensures traceability and transparency. Lastly, due to its tamper-proof design and safe storage, BC may enable the secure release of software updates to IoT devices. Despite all of the above advantages, BIoT integration may pose several challenges [3; 19; 20; 21; 22; 23]. Mission-critical situations, in particular, raise additional questions. Since BIoT integration is a dynamic process influenced by multiple interrelated factors, adding BC to the IoT ecosystem adds more organizational and technological requirements. Hence, this paper aims to provide a comprehensive survey about BIoT integration challenges. Consequently, this paper focuses on the following research questions:  
RQ1: What are the current challenges that face BIoT integration? RQ2: What recommendations have been provided in the literature to overcome these challenges? RQ3: What are the future concerns and research trends for BIoT integration? This paper has several key contributions. Firstly, although BC has been in use for some years, little thorough research on BIoT challenges exists. This article provides a comprehensive survey of BIoT challenges based on a survey of the existing literature on BIoT integration. This survey might be one of several studies that look into these issues in depth. Seven challenges categories were identified in this paper: security, privacy preservation, technical considerations, scalability, computational processing, characteristic considerations, regulations and guidelines, and BIoT design. Secondly, in addition to exploring the problems of BIoT, this paper also reports the recommended solutions to these challenges. The majority of reviewed studies recommended turning the BC phase into another layer (i.e., not an IoT device), such as a fog layer, edge layer, software-defined networking (SDN),or cloud layer as IoT is still in its infancy. Thirdly, the current research problems of IoT decentralization using BC, as well as future challenges in the field, are presented in depth. Seven future BIoT challenges were identified: security, privacy, communication and consensus mechanism, scalability and capability constraints, standardization and regulations, BC platform, and big data. Lastly, potential BIoT integration trends were explored. New BC-based business models, AI, quantum computing, double-chained IoT security, and IoT, BC, and 6G interoperability are among these trends. The paper performed a thorough study of the literature by searching the related papers in major scholarly databases (IEEE Xplore, Springer Link, Wiley Online Library, ACM digital library, MDPI Online, Science Direct, Emerald Insight, and SAGE Publication) to identify and consider the current state of BIoT challenges, as well as future research directions. According to the databases scanned, the use of various BC platforms has been the subject of several journal and conference publications in the field of BIoT such as Bitcoin, Ethereum, Multichain, and Hyperledger Fabric. Table 1 summarizes the abbreviations that appeared in this article. The remainder of the article is structured as follows: Section 2 presents the background and related work; Section 3 responds to the research questions; future research trends and directions are explored in Section 4; the findings' discussion and limitations are presented in Section 5; Section 6 concludes the paper.