| As a national strategic advanced technology,blockchain is the core of trust construction,data interaction,and value transmission for the distributed trustless network.The enterprise consortium blockchain is the advocated developing blockchain service platform and application scheme in China,widely applied in digital finance,energy market,e-government,supply chain,and other key industries.The existing consortium blockchain system completes distributed state consistency only under a small number of nodes by deploying the Byzantine-fault-tolerance consensus protocol.It stores blocks chained sequentially in time based on the hash function and timestamp technologies.It ensures strong intra-system security and inter-system isolation by using heterogeneous underlying technologies(e.g.,consensus protocols and cryptographic algorithms).Due to these actualities,it cannot meet the demands of diversified applications,such as large-scale node access,high-performance transaction processing,and reliable cross-chain interaction.As a result,these difficulties can be summarized as the scalability optimization issue for the consortium blockchain system,corresponding to the network scalability optimization,performance scalability optimization,and system horizontal scalability optimization.For the issues above,researchers have proposed some optimization schemes with the following limitations.(1)For network scalability optimization,existing Byzantine-fault-tolerance consensus protocols always independently optimize network scalability or consensus fault-tolerance rate for the consortium blockchain system but ignores the relationship and collaborative optimization between them.Moreover,it requires high consensus fault tolerance for the consortium blockchain system with a large number of nodes access who may perform Byzantine behavior.(2)For performance scalability optimization,the blockchain sharding protocols are the most promising optimization solution to achieve high performance without reducing the decentralization.For all of these protocols focused on the public blockchain,it will incur high computational power and time costs by using these protocols to the consortium blockchain system straightway.(3)For system horizontal scalability optimization,existing notary/relay-based cross-chain interaction protocols have solved the transaction atomicity issue,while they are the semicentralized optimization solutions that destroy the distribution and lead to the data authenticity challenge.Besides,these protocols are not applied for the one-to-many cross-chain interaction mode,where the incentive fairness guarantee for large-scale cross-chain transactions is ignored.To address the limitations above,this dissertation studies the network scalability optimization(network capacity scaling),performance scalability optimization(transaction throughput improvement),and system horizontal scalability optimization(one-to-many large-scale cross-chain interaction)of the consortium blockchain system.It proposes a multi-layer collaborative optimization mechanism oriented towards the consortium blockchain system architecture and evaluates the performances of this mechanism,such as scalability,fault tolerance,fairness,and security.The main contributions of this dissertation are as follows.(1)In order to address the issues of large-scale node access and low consensus faulttolerance rate,a trusted Byzantine consensus protocol for the consensus layer of the consortium blockchain system is proposed,and a hybrid reputation calculation model for nodes is designed.Specifically,this protocol both scales the network capacity and improves the fault-tolerance rate simultaneously by selecting the nodes with high hybrid reputation values as the consensus participants to perform the practical Byzantine-fault-tolerance consensus protocol.Extensive simulations prove that this protocol allows a large number of nodes to access the consortium blockchain system and has an extremely high consensus fault tolerance.In an ideal consortium blockchain system with 10,000 nodes,the consensus faulttolerance rate of this protocol reaches 98%,which is much higher than that of the practical Byzantine-fault-tolerance consensus protocol,1/3.(2)In order to address the low transaction throughput issue caused by serial massive transaction processing,a hierarchical sharding protocol for the network layer of the consortium blockchain system is proposed.Specifically,this protocol first partitions the whole consortium blockchain system into multiple sub-systems(i.e.,common shardings)based on the identity features of nodes and builds a main sharding consisting of the nodes with high reputation values.Then each common sharding consensuses intra-sharding transactions and generates sub-block independently and in parallel.Finally,the main sharding consensuses these sub-blocks and generates the final block,aiming to improve the overall transaction throughput of the consortium blockchain system.Extensive experiments on a performance test network prove that this protocol linearly improves the transaction throughput.Compared to the classical Elastico sharding protocol,the proposed protocol has significantly lower power and time costs of the sharding establishment,0 and one-tenth,with a similar transaction throughput optimization effect.(3)In order to address the issues of the large-scale one-to-many horizontal cross-chain transactions and their incentive fairness guarantee,a multi-Oracle-based cross-chain interaction protocol for the smart contract layer of the consortium blockchain system is proposed,and an interaction platform with multiple Oracles is deployed.Specifically,this protocol gathers and relays the large-scale cross-chain transactions by deploying and running smart contracts on the Oracles.Moreover,a fair cross-chain data interaction mechanism is designed to distribute the incentive or punishment according to the quality of interacted data to incentivize the rational stakeholders to comply with agreements based on smart contracts under two interaction modes,and its transaction incentive fairness is proved theoretically.Extensive experiments on a cross-chain test network prove that this protocol realizes the one-to-many interaction,and its cross-chain transaction throughput is obviously higher than that of the domestic mainstream consortium blockchain cross-chain platforms,WeCross and BitXHub,maximum at 1.5 times and 3 times respectively.This dissertation focuses on the scalability optimization issue of the consortium blockchain system from a longitudinally layered point of view.Moreover,it considers various metrics,such as scalability,fault tolerance,fairness,and security.Furthermore,theoretical analysis and extensive simulations evaluate the trusted Byzantine consensus protocol for the consensus layer of the consortium blockchain,and extensive experiments on the test networks developed on the mainstream consortium blockchain/Oracle platforms,Hyperledger Fabric,FISCO BCOS,and Truora,evaluate the hierarchical sharding protocol and multi-Oraclebased cross-chain interaction protocol for the network layer and smart contract layer of the consortium blockchain.All in all,the above contributions may provide a theoretical basis and technical support for the secrecy implementation and efficient application of the consortium blockchain system with the goal of Digital China Construction. |
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