## 2 Background and Related Studies
### Hybrid Consensus Mechanism  
The main idea of the hybrid consensus mechanism is to select some nodes as the consensus committee through the PoX consensus mechanism and run the Byzantine consensus mechanism inside the committee to complete the generation of blocks. [PERSON] et al. [37] first combined the classical distributed consistency algorithm PBFT with blockchain and proposed the PeerCensus consensus algorithm. Bitcoin is used as the underlying chain to select a certain number of nodes and complete the generation of the final block through the Chain Agreement (CA) algorithm after their identity authentication. [PERSON] et al. [38] proposed the Hybrid Consensus mechanism, which realized state machine replication in an unauthorized environment by using workload proof. Hybrid Consensus for the first time uses a formal security model and modular design to model the hybrid consensus mechanism and proves that it can meet the safety characteristics such as consistency and activity. [PERSON] et al. [39] proposed ELASTICO, a fragmentation consensus mechanism, which divides nodes participating in the consensus into multiple groups, outputs a block from each group, and then obtains the total block. [PERSON] et al. [40] proposed the Rapid-Chain consensus mechanism, which realized computing sharing, communication sharing, and storage sharing. Its main modules include startup, consensus, and reconfiguration. [PERSON] [41] proposed a Proof of QoS (PoQ) based on Quality of Service (QoS). In this validation protocol, the whole network is divided into several small regions, each region specifies a node according to its QoS, and then runs deterministic Byzantine fault tolerant consensus among all the specified nodes. Although the above-mentioned consensus mechanisms on the indices such as security and efficiency have excellent performance, but the consensus mechanism is still facing single-chain or homogeneous blockchain, they cannot be directly applied to multilevel heterogeneous and cross-blockchain application scenarios of governing blockchain by blockchain. They still need a safe, efficient, and scalable cross-blockchain mechanism for governing blockchain by blockchain frameworks. One of the key distinguishing features that hyper ledger supports for its users is smart contracts. The concept of smart contracts was introduced by [PERSON] in 1994 who defined it as \"a computerized transaction protocol that executes the terms of a contract\". The primary objective of introducing smart contracts was to facilitate the execution of scripts stored in the blockchain without the need for an intermediate entity. Transactions: a transaction is a signed package of data that contains the following components: the signature of the sender and recipient of the message. The amount of ether to be transferred to the data field (optional). GASPRICE: fee required per computational step required for the sender to pay. STARTGAS: represents the max number of computational steps allowed for the transaction to execute. The data field is the key field that the contracts use to read whenever a smart contract is addressed [42; 43; 44; 45; 46]. IIoT Security Threats IIoT solutions consist of industrial systems that connect to cloud for data collection and analysis purposes. IIoT is similar to the traditional Industrial Control Systems (ICS) although the tight security restriction applied in ICS cannot be applied to IIoT environments naturally. This is due to the necessity of cloud computing requiring IIoT devices to have direct access to the internet. This is different from the traditional ICS environments that require different zoning and in-depth defense frameworks. ICS environments differ from the standard enterprise environments in many ways, and below are some of the key differences [47; 48; 49; 50]. Risk level: significant impact on human lives and possibly the nation. Performance Requirements: requires real-time analysis as performance issues can affect the operations and hence can be risky to the organization.