# IoT-Chain and Monitoring-Chain Using Multilevel Blockchain for IoT Security
## 2 Related Work
However, in all of the above methods, the blockchain does not work in IoT devices, and vulnerabilities exist, as illustrated in Figure 1. Regarding blockchains based on sharding, OmniLedger [31], RapidChain [32], and RepChain [33] are limited to cryptocurrency applications. RepChain also defines the reputation by using the trust and activeness of validators, based on their decisions on the list of transactions. RepChain uses the accumulated reputation values for balanced sharding and leader selection. However, when the leader node is selected through the accumulated values of the reputation, the randomness is reduced. In this study, a leader node was randomly selected using VRF. HomeChain [34], which is a novel attribute-based access control scheme for IoT systems [35], and Fabric-IoT [36], have been used for the access control of IoT devices based on blockchain. In this study, the access control function for the user is implemented for security by using the smart contract of the blockchain, but forgery and falsification of the sensor data storage generated by the IoT device mean that stability is not guaranteed. Studies on consensus algorithms have been conducted, including PoBT [37], Algorand [38], and Tendermint [39]. PoBT consists of a structure that is suitable for IoT scalability and performance based on the consensus structure of Hyperledger Fabric, and Algorand is a VRF-based consensus algorithm. Tendermint is a PBFT-based consensus algorithm. In this study, although Hyperledger Fabric is used, a new blockchain that operates on IoT devices is proposed. A random-based consensus algorithm is suitable for IoT performance. Unlike PBFT, a consensus method and lightweight method that are suitable for network traffic and sensor generation speed are proposed. Moreover, as opposed to Algorand, this study presents a blockchain that is suitable for IoT devices by selecting a consensus leader node based on the size of a value without using VRF to form a committee. Reference [40] proposed a consensus algorithm that improves the performance of the routing algorithm. A lightweight blockchain-based secure routing algorithm has been proposed to address the challenges [41] of swarm unmanned aircraft system (UAS) networking, and a proof of traffic consensus algorithm that reduces passive broadcasts is used. Reference [42] proposed a consensus construction with high verification efficiency with base stations for cellular network connection. Unlike the above paper, in this paper, we propose an efficient group authentication method based on the consensus algorithm and Schnorr signature based on lightweight communication in IoT-Chain. Figure 1: Comparison of IoT data management methods according to architecture (red indicates vulnerability). Reference [43] proposed a blockchain that requires minimal hardware and software performance. To this end, we propose a witness protocol, which can maintain a blockchain with minimal hardware, and does not require additional equipment or access to a centralized network. In contrast, the blockchain in this paper is a multi-level blockchain configuration so that blockchain nodes can participate in the maintenance of the blockchain and participate in the consensus algorithm and data verification process.