摘要:Multi-valued validated asynchronous Byzantine agreement (MVBA), proposed in the elegant work of Cachin et al. (CRYPTO ’01), is fundamental for critical fault-tolerant services such as atomic broadcast in the asynchronous network.

摘要:The surprising success of cryptocurrencies has led to a surge of interest in deploying large scale, highly robust, Byzantine fault tolerant (BFT) protocols for mission-critical applications, such as financial transactions. Although the conventional wisdom is to build atop a (weakly) synchronous protocol such as PBFT (or a variation thereof), such protocols rely critically on network timing assumptions, and only guarantee liveness when the network behaves as expected. We argue these protocols are ill-suited for this deployment scenario. We present an alternative, HoneyBadgerBFT, the first practical asynchronous BFT protocol, which guarantees liveness without making any timing assumptions. We base our solution on a novel atomic broadcast protocol that achieves optimal asymptotic efficiency. We present an implementation and experimental results to show our system can achieve throughput of tens of thousands of transactions per second, and scales to over a hundred nodes on a wide area network. We even conduct BFT experiments over Tor, without needing to tune any parameters. Unlike the alternatives, HoneyBadgerBFT simply does not care about the underlying network.

摘要:We present BEAT, a set of practical Byzantine fault-tolerant (BFT) protocols for completely asynchronous environments. BEAT is flexible, versatile, and extensible, consisting of five asynchronous BFT protocols that are designed to meet different goals (e.g., different performance metrics, different application scenarios). Due to modularity in its design, features of these protocols can be mixed to achieve even more meaningful trade-offs between functionality and performance for various applications. Through a 92-instance, five-continent deployment of BEAT on Amazon EC2, we show that BEAT is efficient: roughly, all our BEAT instances significantly outperform, in terms of both latency and throughput, HoneyBadgerBFT, the most efficient asynchronous BFT known.

摘要:2008 年比特币出现以来,研究学者相继提出了多种分布式账本技术,其中,区块链是当前分布式账本最 主要的实现形式之一.但当前区块链中存在一个核心问题:可扩展性瓶颈.具体而言,区块链的吞吐量严重不足,且其 交易确认也较为缓慢,这些因素极大地限制了它的实际应用.在此背景下,基于 DAG(有向无环图)的分布式账本因其 具有高并发特性,有望突破传统区块链中的性能瓶颈,从而受到了学术界和产业界越来越多的关注和研究.在基于 DAG 的分布式账本中,最为核心和关键的技术是其共识机制,为此,对该关键技术进行了系统深入的研究.首次从共 识形态出发将现有基于 DAG 的分布式账本分为以下 3 类:基于主干链的 DAG 账本;基于平行链的 DAG 账本;基于 朴素 DAG 的账本.在此基础上,对不同类型的共识机制本质原理及特性进行了深入阐述,并从不同层面对它们进行 了详细的对比分析.最后,指出基于 DAG 的共识机制研究中存在的问题与挑战,并给出进一步的研究方向.

摘要:We propose separating the task of reliable transaction dissemination from transaction ordering, to enable high-performance Byzantine fault-tolerant quorum-based consensus. We design and evaluate a mempool protocol, Narwhal, specializing in high-throughput reliable dissemination and storage of causal histories of transactions. Narwhal tolerates an asynchronous network and maintains high performance despite failures. Narwhal is designed to easily scale-out using multiple workers at each validator, and we demonstrate that there is no foreseeable limit to the throughput we can achieve. Composing Narwhal with a partially synchronous consensus protocol (Narwhal-HotStuff) yields significantly better throughput even in the presence of faults or intermittent loss of liveness due to asynchrony. However, loss of liveness can result in higher latency. To achieve overall good performance when faults occur we design Tusk, a zero-message overhead asynchronous consensus protocol, to work with Narwhal. We demonstrate its high performance under a variety of configurations and faults. As a summary of results, on a WAN, Narwhal-Hotstuff achieves over 130,000 tx/sec at less than 2-sec latency compared with 1,800 tx/sec at 1-sec latency for Hotstuff. Additional workers increase throughput linearly to 600,000 tx/sec without any latency increase. Tusk achieves 160,000 tx/sec with about 3 seconds latency. Under faults, both protocols maintain high throughput, but Narwhal-HotStuff suffers from increased latency.

摘要:Abstract. A new system, the Swirlds hashgraph consensus algorithm, is proposed for replicated state machines with guaranteed Byzantine fault tolerance. It achieves fairness, in the sense that it is difficult for an attacker to manipulate which of two transactions will be chosen to be first in the consensus order. It has complete asynchrony, no leaders, no round robin, no proof-of-work, eventual consensus with probability one, and high speed in the absence of faults. It is based on a gossip protocol, in which the participants don’t just gossip about transactions. They gossip about gossip. They jointly build a hashgraph reflecting all of the gossip events. This allows Byzantine agreement to be achieved through virtual voting. Alice does not send Bob a vote over the Internet. Instead, Bob calculates what vote Alice would have sent, based on his knowledge of what Alice knows. This yields fair Byzantine agreement on a total order for all transactions, with very little communication overhead beyond the transactions themselves.

摘要:This paper presents Conflux, a scalable and decentralized blockchain system with high throughput and fast confirmation. Conflux operates with a novel consensus protocol which optimistically processes concurrent blocks without discarding any as forks and adaptively assigns weights to blocks based on their topologies in the Con- flux ledger structure (called Tree-Graph). The adaptive weight mechanism enables Conflux to detect and thwart liveness attack by automatically switching between an optimistic strategy for fast confirmation in normal scenarios and a conservative strategy to ensure consensus progress during liveness attacks. We evaluated Conflux on Amazon EC2 clusters with up to 12k full nodes. The consensus protocol of Conflux achieves a block throughput of 9.6Mbps with 20Mbps network bandwidth limit per node. On a combined workload of payment transactions and Ethereum history transactions, the end-to-end system of Conflux achieves the throughput of up to 3480 transactions per second while confirming transactions under one minute.

摘要:We present DAG-Rider, the first asynchronous Byzantine Atomic Broadcast protocol that achieves optimal resilience, optimal amortized communication complexity, and optimal time complexity. DAG-Rider is post-quantum safe and ensures that all values proposed by correct processes eventually get delivered. We construct DAG-Rider in two layers: In the first layer, processes reliably broadcast their proposals and build a structured Directed Acyclic Graph (DAG) of the communication among them. In the second layer, processes locally observe their DAGs and totally order all proposals with no extra communication.

摘要:The paper presents Tendermint, a new protocol for ordering events in a distributed network under adversarial conditions. More commonly known as Byzantine Fault Tolerant (BFT) consensus or atomic broadcast, the problem has attracted significant attention in recent years due to the widespread success of blockchain-based digital currencies, such as Bitcoin and Ethereum, which successfully solved the problem in a public setting without a central authority. Tendermint modernizes classic academic work on the subject and simplifies the design of the BFT algorithm by relying on a peer-to-peer gossip protocol among nodes.

摘要:In the past five years or so, numerous blockchain projects have made tremendous progress towards improving permissioned consensus protocols (partly due to their promised applications in Proof-of-Stake cryptocurrencies). Although a significant leap has silently taken place in our understanding of consensus protocols, it is rather difficult to navigate this body of work, and knowledge of the new techniques appears scattered. In this paper, we describe an extremely simple and natural paradigm called Streamlet for constructing consensus protocols. Our protocols are inspired by the core techniques that have been uncovered in the past five years of work; but to the best of our knowledge our embodiment is simpler than ever before and we accomplish this by taking a “streamlining” idea to its full potential. We hope that our textbook constructions will help to decipher the past five years of work on consensus partly driven by the cryptocurrency community — in particular, how remarkably simple the new generation of consensus protocols has become in comparison with classical mainstream approaches such as PBFT and Paxos.

摘要:Classical-style BFT protocols use two or more rounds of voting to confirm each block, e.g., in PBFT, they are called the “prepare” round and the “commit” round respectively. Recently, an elegant pipelining idea came out of the cryptocurrency community, i.e., if each block required two rounds of voting, why not piggyback the second round on the next block’s voting? We refer to this idea as the pipelined-BFT paradigm. We describe a simple partially synchronous blockchain protocol called PaLa that is inspired by the pipelined-BFT paradigm. In PaLa, a proposer proposes a block extending the freshest notarized chain seen so far. Consensus nodes vote on the proposal if certain conditions are met. When a block gains at least 23n votes it becomes notarized. A block becomes finalized if the next immediate block becomes notarized too. We propose a conceptually simple and provably secure committee rotation algorithm for PaLa. We also describe a generalization called “doubly-pipelined PaLa” that is geared towards settings that require high throughput.

摘要:We present HotStu, a leader-based Byzantine fault-tolerant replication protocol for the partially synchronous model. Once network communication becomes synchronous, HotStu enables a correct leader to drive the protocol to consensus at the pace of actual (vs. maximum) network delay—a property called responsiveness—and with communication complexity that is linear in the number of replicas. To our knowledge, HotStu is the rst partially synchronous BFT replication protocol exhibiting these combined properties. HotStu is built around a novel framework that forms a bridge between classical BFT foundations and blockchains. It allows the expression of other known protocols (DLS, PBFT, Tendermint, Casper), and ours, in a common framework. Our deployment of HotStu over a network with over 100 replicas achieves throughput and latency comparable to that of BFT-SMaRt, while enjoying linear communication footprint during leader failover (vs. cubic with BFTSMaRt).

摘要:The HotStuff protocol is a breakthrough in Byzantine Fault Tolerant (BFT) consensus that enjoys both responsiveness and linear view change. It creatively adds an additional round to classic BFT protocols (like PBFT) using two rounds. This brings us to an interesting question: Is this additional round really necessary in practice? In this paper, we answer this question by designing a new two-round BFT protocol called FastHotStuff, which enjoys responsiveness and efficient view change that is comparable to linear view change in terms of performance. Compared to (three-round) HotStuff, Fast-HotStuff has lower latency and is more robust against performance attacks that HotStuff is susceptible to.

摘要:This paper describes a new replication algorithm that is able to tolerate Byzantine faults. We believe that Byzantinefault-tolerant algorithms will be increasingly important in the future because malicious attacks and software errors are increasingly common and can cause faulty nodes to exhibit arbitrary behavior. Whereas previous algorithms assumed a synchronous system or were too slow to be used in practice, the algorithm described in this paper is practical: it works in asynchronous environments like the Internet and incorporates several important optimizations that improve the response time of previous algorithms by more than an order of magnitude. We implemented a Byzantine-fault-tolerant NFS service using our algorithm and measured its performance. The results show that our service is only 3% slower than a standard unreplicated NFS.

摘要:ecently, the Industrial Internet of Things plays a vital role in the new round of technology innovation and industry competition, where the identity resolution system is its key component. However, there are some problems in the existing Handle-based identity resolution architecture. Therefore, a trusted identifier co-governance architecture is proposed, and a prototype system is designed and implemented in this article. Specifically, we design a blockchain-based decentralized framework for identifier service, identifier life cycle management based on smart contract, and a data storage mechanism for a trusted identifier. The whole architecture could solve the problems of single point of failure, data tampering, and governance deviation, and reduce the trust cost in the process of data circulation. The simulation results reveal that the system has achieved good results in terms of delay and throughput.