CRBFT:A Byzantine Fault-Tolerant Consensus Protocol Based on Collaborative Filtering Recommendation for Blockchains

Blockchain has been widely used in finance,the Internet of Things(IoT),supply chains,and other scenarios as a revolutionary technology.Consensus protocol plays a vital role in blockchain,which helps all participants to maintain the storage state consistently.However,with the improvement of network environment complexity and system scale,blockchain development is limited by the performance,security,and scalability of the consensus protocol.To address this problem,this paper introduces the collaborative filtering mechanism commonly used in the recommendation system into the Practical Byzantine Fault Tolerance(PBFT)and proposes a Byzantine fault-tolerant(BFT)consensus protocol based on collaborative filtering recommendation(CRBFT).Specifically,an improved collaborative filtering recommendation method is designed to use the similarity between a node’s recommendation opinions and those of the recommender as a basis for determining whether to adopt the recommendation opinions.This can amplify the recommendation voice of good nodes,weaken the impact of cunningmalicious nodes on the trust value calculation,andmake the calculated resultsmore accurate.In addition,the nodes are given voting power according to their trust value,and a weight randomelection algorithm is designed and implemented to reduce the risk of attack.The experimental results show that CRBFT can effectively eliminate various malicious nodes and improve the performance of blockchain systems in complex network environments,and the feasibility of CRBFT is also proven by theoretical analysis.

A Fault Detection Mechanism in Erasure-Code Byzantine Fault-Tolerance Quorum

Fault-tolerance is increasingly significant for large-scale storage systems in which Byzantine failure of storage nodes may happen. Traditional Byzantine Quorum systems that tolerate Byzantine failures by using replication have two main limitations： low space-efficiency and static quorum variables. We propose an Erasure-code Byzantine Fault-tolerance Quorum that can provide high reliability with far lower storage overhead than replication by adopting erasure code as redundancy scheme. Through read/write operations of clients and diagnose operation of supervisor, our Quorum system can detect Byzantine nodes, and dynamically adjust system size and fault threshold. Simulation results show that our method improves performance for the Quorum with relatively small quorums.

区块链BFT共识算法研究进展

自2008年比特币问世后,区块链逐渐成为学术界的研究热点,共识算法作为区块链的关键技术,受到了越来越多研究者的重视。由于区块链运行环境复杂多变,容易在系统中引入拜占庭节点,因此区块链拜占庭容错共识算法是必须要攻克的难关。文中系统地总结了区块链拜占庭容错共识算法的研究进展,以期为未来共识算法的创新提供参考。首先,梳理了现有的区块链拜占庭容错共识算法的四大派别,引出了BFT共识算法;其次,回顾了经典BFT共识算法PBFT中的几个重要临界值及其正确性证明;再次,提出了BFT共识算法具有去中心化、效能、安全性和容错率ntg四大优化目标;然后,基于共识轮次、共识节点个数、底层硬件、通信模式或加密算法、出错概率等维度,归纳出BFT共识算法的5种优化思路;最后,对10种经典BFT共识算法进行了详细分析与性能对比。

结合动态信用机制的PBFT算法优化方案

实用拜占庭容错(PBFT)共识算法被广泛应用于金融机构、电子货币行业、农产品溯源等领域,但存在灵活性较差、拜占庭节点处理方式不足、通信开销和网络时延较大等问题。提出基于动态机制与信用积分机制的实用拜占庭容错共识算法DT-PBFT。引入动态加入或退出机制,使集群内的节点可以按需自由加入或退出,增加信用积分机制,通过分层机制将节点按可信任程度分为备用主节点层、中间层、警告层和清理层,采用惩罚机制降低节点连续作恶的可能性,以保证从备用主节点层中优先选择最优的主节点,大幅提高共识效率。同时,通过剔除网络清理层中的拜占庭节点,提高算法的运行效率。在此基础上,通过优化一致性协议对共识流程进行改进,减少一轮全网节点信息交互确认流程,从而降低通信开销。实验结果表明,当节点数为22时,相比DGPBFT、DDBFT和PBFT算法,DT-PBFT算法具有较优的灵活性,吞吐量和交易请求有效完成率分别为292 transaction/s和83.4%,CPU利用率为50%,相比PBFT算法,延迟降低了350 ms。

BVDFed:Byzantine-resilient and verifiable aggregation for differentially private federated learning

Federated Learning(FL)has emerged as a powerful technology designed for collaborative training between multiple clients and a server while maintaining data privacy of clients.To enhance the privacy in FL,Differentially Private Federated Learning(DPFL)has gradually become one of the most effective approaches.As DPFL operates in the distributed settings,there exist potential malicious adversaries who manipulate some clients and the aggregation server to produce malicious parameters and disturb the learning model.However,existing aggregation protocols for DPFL concern either the existence of some corrupted clients(Byzantines)or the corrupted server.Such protocols are limited to eliminate the effects of corrupted clients and server when both are in existence simultaneously due to the complicated threat model.In this paper,we elaborate such adversarial threat model and propose BVDFed.To our best knowledge,it is the first Byzantine-resilient and Verifiable aggregation for Differentially privateFEDerated learning.In specific,wepropose Differentially Private Federated Averaging algorithm(DPFA)asour primary workflow of BVDFed,which ismore lightweight and easily portable than traditional DPFL algorithm.We then introduce Loss Score to indicate the trustworthiness of disguised gradients in DPFL.Based on Loss Score,we propose an aggregation rule DPLoss to eliminate faulty gradients from Byzantine clients during server aggregation while preserving the privacy of clients'data.Additionally,we design a secure verification scheme DPVeri that are compatible with DPFA and DPLoss to support the honest clients in verifying the integrity of received aggregated results.And DPVeri also provides resistance to collusion attacks with no more than t participants for our aggregation.Theoretical analysis and experimental results demonstrate our aggregation to be feasible and effective in practice.

区块链共识机制综述

区块链能够有效融合物联网、5G、大数据和人工智能等技术,在新型基础设施建设中具有重要作用。共识机制作为区块链的核心技术,能够保障区块链数据库的一致性和正确性,从而决定区块链的安全性、扩展性、吞吐量等相关性能。根据区块链共识机制的技术路线,将其细分为3类单一共识机制和6类混合共识机制。从原理实现角度,系统描述共识机制的理论技术,归纳节点达成一致所需的运算操作并评价共识机制的优缺点。从工程应用角度,具体分析共识机制的应用情况,介绍区块链项目并对比共识机制的关键性能。针对现有共识机制研究中存在的能耗与效率问题给出相应的解决方案,并对其奖惩制度、网络分片与存储分片技术等下一步研究方向进行展望。

基于投票机制的拜占庭容错共识算法

针对现有的区块链中实用拜占庭容错(PBFT)共识算法、基于动态授权的拜占庭容错(DDBFT)共识算法、联盟拜占庭容错(CBFT)共识算法普遍存在能耗高、效率低、扩展性差等问题,通过引入投票机制,提出了基于投票机制的拜占庭容错(VPBFT)共识算法。首先,以PBFT算法为基础,将网络中的节点划分为四类具有不同职责的节点。其次,算法中的投票节点具有投票和评分权,监督生产节点诚实可靠地生产数据块;生产有效的数据块的生产节点优先进入下一轮,候选节点能够被选为生产节点,而普通节点则能够成为投票节点或候选节点。最后,不同类型的节点之间具有一定的数量关系,能够在不同类型节点的数目或网络中的节点总数发生变化时动态调整参数,从而使得算法适应动态网络。通过性能仿真分析可知,VPBFT算法相较于PBFT、 DDBFT、CBFT等共识算法,具有低能耗、低时延、高容错性和高动态性。

面向服务计算的拜占庭容错方案及其正确性证明

针对现有拜占庭容错协议的假设(要求被保护的对象是被动的和独立的)不适用于服务计算等新兴计算模型的问题,提出一种面向服务计算的拜占庭容错协议。该协议在服务请求方和服务提供方两端均创建服务复制品,采用基于状态机的主动复制技术,在服务复制品间进行三轮通信,就该请求的编号和内容达成一致,随后该请求被提交给上层应用逻辑处理;收到应答后,服务请求方的复制品进行三轮通信就应答的编号和内容达成一致后接受该应答。针对现有面向服务计算的拜占庭容错协议只有简单的正确性推理缺乏形式化验证的问题,采用I/O自动机和模拟关系方法进行正确性证明,更加严谨和正式。构造一个高度抽象的简单I/O自动机S,此自动机满足安全性和及时性;将协议中的各方分解成若干简单I/O自动机:前端自动机、后端自动机和多播通道自动机;最后用模拟关系方法证明各成员自动机构成的系统实现了自动机S,从而证明协议的正确性。使用I/O自动机可以精确描述协议,以此为基础进行证明比感性推理的证明方法更加规范。

基于拜占庭容错的软件定义网络控制面的抗攻击性研究

软件定义网络(SDN)的集中化控制面给网络管理带来了很大的便利,但也引入了很多安全隐患。针对控制器的单点故障、未知的漏洞和后门、静态配置等安全性问题,提出一种基于拜占庭协议的安全结构,控制器之间执行拜占庭协议,每个交换设备由一个控制器视图管理,多控制器裁决后给出控制信息。此外,将动态性、异构性引入到结构中,打破了攻击链,增强了网络的主动防御能力;通过对控制器异构性的量化,设计了两阶段控制器视图的选举算法,保证了网络的可用性和视图的安全性。仿真结果表明,与传统结构相比,所提结构的抗攻击能力更强。

区块链与秘密分享融合技术综述

近年来,区块链的持续发展使得应用密码学受到广泛关注,同时引起更多国内外学者对信息安全的重点研究。秘密分享技术作为构建安全多方计算协议的基础原语,具备门限特性且在应用中具有拜占庭容错性特点。由于在信息安全三要素,即机密性、完整性和可用性上的契合,区块链和秘密分享存在关联性和互补性。现有研究通过融合区块链和秘密分享技术提升了系统稳定性和效率,取得对分布式系统研究的突破。阐述区块链共识算法与拜占庭容错协议之间的关系,分析秘密分享对于实现权益证明共识算法的重要性。总结基于智能合约实现的不同种类的秘密分享体制,以及运用智能合约和秘密分享技术构建的密码协议和具体应用。说明公共通告栏与区块链、秘密分享技术之间的联系,综述使用秘密分享技术优化区块链数据存储的研究,并列举融合区块链存储和秘密分享技术可解决的实际应用。在此基础上,介绍区块链与秘密分享的功能特性和性能指标,展望两者融合的未来发展方向。

一种结合BLS签名的可拜占庭容错Raft算法

针对Raft算法中的拜占庭容错问题,提出结合BLS签名的拜占庭容错(Raft Byzantine fault tolerance, RBFT)算法.首先,利用BLS签名实现阈值签名,将投票过程转化为阈值签名过程,并将该过程与Raft算法的AppendEntries消息和RequestVote消息结合,尽可能地减弱容错过程对共识效率的影响;其次,通过增量哈希引入安全状态,保证了日志的不可篡改性;接着引入客户端对Leader节点的动态监控,以避免拜占庭Leader节点消极反馈的发生,进一步保证了算法的活性;最后,由本地多节点仿真实验表明:RBFT算法有效提升了数据吞吐量和可拓展性,并降低了交易延迟.

具有监督机制的高效拜占庭容错算法

共识机制作为区块链技术的核心内容,在不同应用领域各有差异。针对联盟链应用场景,应用广泛的实用拜占庭容错(PBFT)算法仍然存在效率及安全性问题,因此从网络模型、共识本质及安全攻击等角度对PBFT算法进行研究,提出了一种高效监督拜占庭容错算法(Efficient Supervised Byzantine Fault Tolerance,ES-BFT)。针对效率问题,ES-BFT算法将节点随机划分为多个节点簇,设置信誉值,通过信誉值从节点簇中选举共识节点、监督节点,尽可能提升共识节点的高效性及可靠性;监督节点对共识节点进行监控,避免了在Global Stabilization Time(GST)开始之前共识节点可能遭遇的系统不协调问题,进一步保证算法的安全性;通过实验表明ES-BFT算法在效率及安全性上较PBFT算法有所提升,并且免疫在GST之前的攻击所导致的系统不协调问题。

A survey on blockchain consensus mechanism: research overview, current advances and future directions

Purpose-As the core technology of blockchain,various consensus mechanisms have emerged to satisfy the demands of different application scenarios.Since determining the security,scalability and other related performance of the blockchain,how to reach consensus efficiently of consensus mechanism is a critical issue in the blockchain.Design/methodology/approach-The paper opted for a research overview on the blockchain consensus mechanism,including the consensus mechanisms’consensus progress,classification and comparison,which are complemented by documentary analysis.Findings-This survey analyzes solutions for the improvement of consensus mechanisms in blockchain that have been proposed during the last few years and suggests future research directions around consensus mechanisms.First,the authors outline the consensus processes,the advantages and disadvantages of the mainstream consensus mechanisms.Additionally,the consensus mechanisms are subdivided into four types according to their characteristics.Then,the consensus mechanisms are compared and analyzed based on four evaluation criteria.Finally,the authors summarize the representative progress of consensus mechanisms and provide some suggestions on the design of consensus mechanisms to make further advances in this field.Originality/value-This paper summarizes the future research development of the consensus mechanisms.