Byzantine Fault-tolerant Protocols Research Articles

TortoiseBFT: An asynchronous consensus algorithm for IoT system

Traditional partial synchronous Byzantine fault tolerant (BFT) protocols are confronted with new challenges when applied to large-scale networks like IoT systems, which bring about rigorous demand for the liveness and consensus efficiency of BFT protocols in asynchronous network environments. HoneyBadgerBFT is the first practical asynchronous BFT protocol, which employs a reliable broadcast protocol (RBC) to broadcast transactions and an asynchronous binary agreement protocol (ABA) to determine whether transactions should be committed. DumboBFT is a follow-up proposal that requires fewer instances of ABA and achieves higher throughput than HoneyBadgerBFT, but it does not optimize the communication overhead of HoneyBadgerBFT.In this paper, we propose TortoiseBFT, a high-performance asynchronous BFT protocol with three stages. We can significantly reduce communication overhead by determining the order of transactions first and requesting missing transactions after. Our two-phase transaction recovery mechanism enables nodes to recover missing transactions by seeking help from 2f+1 nodes. To improve the overall throughput of the system, we lower the verification overhead of threshold signatures in HoneyBadgerBFT, DumboBFT, and DispersedLedger from On3 to On2. We develop a node reputation model that selects producers with stable network conditions, which helps to reduce the number of random lotteries. Experimental results show that TortoiseBFT improves system throughput, reduces transaction delays, and minimizes communication overhead compared to HoneyBadgerBFT, DumboBFT, and DispersedLedger.

BFTDiagnosis: An automated security testing framework with malicious behavior injection for BFT protocols

In peer-to-peer computing networks, Byzantine Fault Tolerance (BFT) protocols are a popular solution to ensure the consistency security in the presence of some malicious nodes, thus are widely employed in blockchain systems. However, BFT protocols still face various security threats in practice. Currently, testing the security of BFT protocols often requires manual operations. I.e., it lacks comprehensive automation testing techniques. This makes it difficult to cover various scenarios of malicious node behaviors. Therefore, it is an urgent requirement to design an automated testing framework that can comprehensively and efficiently evaluate the security of BFT protocols.This paper proposes BFTDiagnosis, an automated security testing framework with malicious behavior injection for BFT protocols. The framework can automatically configure and initiate protocol testing tasks, and construct consensus nodes to execute different BFT protocols. During testing, consensus nodes can inject malicious behaviors based on pattern matching strategies and malicious behavior triggering mechanisms to simulate various malicious scenarios. Through an Analyzer, BFTDiagnosis can collect protocol runtime data from consensus nodes and calculate four security quantification indicators to evaluate protocol performance.We conducted a load consumption evaluation of BFTDiagnosis. The results indicate its acceptable performance. Additionally, we tested PBFT, Basic-HotStuff, and Chained-HotStuff protocols using the BFTDiagnosis framework, validating the effectiveness of the framework and the rationality of security quantification indicators. Finally, we compared it with nine related technologies and found that BFTDiagnosis is good at testing scenario comprehensiveness and fault localization capability, and can intuitively evaluate the security of BFT protocols through four quantification indicators. The above results show that BFTDiagnosis is an effective and comprehensive security testing framework for BFT protocols.

Rashnu: Data-Dependent Order-Fairness

Distributed data management systems use state Machine Replication (SMR) to provide fault tolerance. The SMR algorithm enables Byzantine Fault-Tolerant (BFT) protocols to guarantee safety and liveness despite the malicious failure of nodes. However, SMR does not prevent the adversarial manipulation of the order of transactions, where the order assigned by a malicious leader differs from the order in that transactions are received from clients. While order-fairness has been recently studied in a few protocols, such protocols rely on synchronized clocks, suffer from liveness issues, or incur significant performance overhead. This paper presents Rashnu , a high-performance fair ordering protocol. Rashnu is motivated by the fact that fair ordering among two transactions is needed only when both transactions access a shared resource. Based on this observation, we define the notion of data-dependent order fairness where replicas capture only the order of data-dependent transactions and the leader uses these orders to propose a dependency graph that represents fair ordering among transactions. Replicas then execute transactions using the dependency graph, resulting in the parallel execution of independent transactions. We implemented a prototype of Rashnu where our experimental evaluation reveals the low overhead of providing order-fairness in Rashnu.

An Efficient and Reliable Byzantine Fault Tolerant Blockchain Consensus Protocol for Single-Hop Wireless Networks

An Efficient and Reliable Byzantine Fault Tolerant Blockchain Consensus Protocol for Single-Hop Wireless Networks

SodsBC: A Post-Quantum by Design Asynchronous Blockchain Framework

We present a new framework for asynchronous permissioned blockchain with high performance and post-quantum security. The framework contains two quantum-secure asynchronous Byzantine fault tolerance (aBFT) protocols, SodsBC and SodsBC++. We leverage concurrent preprocessing to accelerate the preparation of three cryptographic objects for the repeated consensus procedure, including common random coins as the needed randomness, secret shares of symmetric encryption keys for censorship resilience, and nested hash values for external validation predicates. The key idea behind our design is that the concurrent preprocessing mechanism can be well-supported by the consensus process of blockchains. The consumed objects in a block have been generated and globally agreed upon in a previous block. All our preprocessed objects utilize proven or commonly believed to be post-quantum cryptographic tools to resist an adversary equipped with quantum computation capabilities. We evaluate our protocols and their competitors in AWS in a typical setting where, the number of participants is 100 and each block part has 20,000 transactions. The results show that SodsBC and SodsBC++ reduce the latency of two state-of-the-art but quantum-sensitive competitors Honeybadger and Dumbo by 53% and 6%, respectively.

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

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

Analytical model for performability evaluation of Practical Byzantine Fault-Tolerant systems

Designing systems tolerant to faults is crucial to assure continuity of service for mission critical applications. However, their implementation may be costly and challenging. In this study, analytical models are presented for performance evaluation of systems equipped with Practical Byzantine Fault-Tolerant consensus protocols. Byzantine Fault Tolerance is particularly compelling, since it can provide a robust consensus mechanism to implement decentralized platforms, like Decentralized Ledger Technology and, notably, blockchains. The performability model is based on continuous-time Markov chains, in which the processes involved follow the exponential distribution. The numerical results presented report an inverse non-linear relation between number of nodes and performability. Performance decreases also as the ratio between break-down rate and repair rate increases.

Privacy-Preserving Asynchronous Federated Learning Framework in Distributed IoT

To solve the data island issue in the distributed Internet of Things (IoT) without privacy leakage, Privacy-Preserving Federated Learning (PPFL) has been extensively explored in both academic and industrial fields. However, existing PPFL solutions still suffer from a single point of failure and incur untrusted aggregation results caused by a malicious central server, and even cause a loss of model accuracy in an asynchronous setting. To solve these issues, we propose a privacy-preserving asynchronous FL scheme by using blockchain. Specifically, we use blockchain to address single points of failure and untrustworthy aggregation results, implement reliable model aggregation utilizing a practical byzantine fault-tolerant protocol in an asynchronous setting, and leverage differential privacy to improve system robustness. Formal security analysis and convergence analysis demonstrate that the proposed scheme is secure and robust, and extensive experiments demonstrate that our scheme can effectively ensure the accuracy of the system when compared with state-of-the-art schemes.

Scalable and fault-tolerant selection method of verification and accounting nodes for permissionless blockchain

The transaction processing mode of the permissionless blockchain with the PoW protocol is to generate transaction block through network-wide competition and perform transaction verification by all the nodes jointly, resulting in wasted computing power resources and low throughput as bottlenecks for its application in industrial fields with high-frequency transactions. In order to enhance the transaction processing performance of the blockchain system and meet the actual security requirements, we propose a scalable and fault-tolerant selection method of verification and accounting nodes. Firstly, combined with the advantages of PoW, we apply the computationally difficult problem in the selection method of the verification set, which can fully utilize computing resources and ensure the efficiency of transaction verification. Afterwards, a fault-tolerant selection method of accounting node is designed by constructing the verifiable random number using threshold signature, which can ensure the robust operation of the system in the presence of malicious nodes. The newly developed method has the following advantages: it has fault-tolerant characteristics; the method can be applied to systems with Byzantine or non-Byzantine errors, and is appropriate for practical application scenarios. It has compatibility, the method can be seamlessly integrated into Byzantine fault tolerance, crash tolerance, threshold voting and other consensus protocols to improve the performance of the protocol. It has versatility, the method can be applied to both single blockchains and sharding blockchains to demonstrate its versatility and flexibility. Finally, the results of the security analysis and experiment show the method is of superiority and effectiveness.

Deterministic or probabilistic? - A survey on Byzantine fault tolerant state machine replication

Byzantine Fault tolerant (BFT) protocols are implemented to guarantee the correct system/application behavior even in the presence of arbitrary faults (i.e., Byzantine faults). Byzantine Fault tolerant State Machine Replication (BFT-SMR) is a known software solution for masking arbitrary faults and malicious attacks (Liu et al., 2020). In this survey, we present and discuss relevant BFT-SMR protocols, focusing on deterministic and probabilistic approaches. The main purpose of this paper is to discuss the characteristics of proposed works for each approach, as well as identify the trade-offs for each different approach.

Reinforced practical Byzantine fault tolerance consensus protocol for cyber physical systems

Cyber–physical systems (CPS) are becoming an essential component of modern life. CPS services enable information to be exchanged between physical devices and virtual systems. The increasing malicious activities causing confidential data leakage and incorrect performance of devices are posing challenges for protection against cyber threats. Therefore, development of effective solutions that can protect both CPS data and data exchange networks are extremely urgent. This study makes some improvements on Practical Byzantine Fault Tolerance (PBFT), and provides a critical analysis of the feasibility of using blockchain technology to protect constrained CPS data. It also justifies the choice of the improved PBFT for implementation on such devices and simulates the main distributed ledger scenarios. The improved PBFT works as follows: first, the client broadcasts the signed transaction data to the entire network, rather than just the master node, followed by a hash value comparison verification process; second, select the master node based on the longest chain principle, and punish the malicious node via the “blacklist” mechanism; third, add the data synchronization and verification process, as well as dynamically entering and leaving nodes via state transitions. Ultimately, the PBFT commit phase is eliminated, resulting in a two-stage process. In comparison to the original PBFT protocol, the Reinforced Practical Byzantine Fault Tolerance (RPBFT) protocol may substantially enhance system throughput and minimize consensus communication time, thereby improving overall system efficiency while guaranteeing security.

Dynamic Protocol Blockchain for Practical Byzantine Fault Tolerance Consensus

This work details the byzantine fault-tolerant protocols that dynamically allow replicas to join and exit. Byzantine fault-tolerant (BFT) protocols and the blockchain now play an essential role in achieving consensus. There are numerous drawbacks to PBFT, despite its multiple positives. The first thing to note is that it runs in an environment completely isolated from the rest of the world. The entire system must be shut down before any nodes can be added or removed. Second, it ensures liveness and safety if no more than (n-1)/3 out of total n replicas, PBFT takes no action to cope with ineffective or malicious counterparts. This is bad for the system and will lead to its eventual failure. These flaws have far-reaching consequences in real life. The Randomization PBFT is an alternative way of dealing with these issues. In recent decades, as computer technology has advanced, so has our reliance on the products, services, and capabilities that computers provide.

A Flexible Sharding Blockchain Protocol Based on Cross-Shard Byzantine Fault Tolerance

Sharding technology is crucial to achieve decentralization, scalability, and security simultaneously. However, existing sharding blockchain schemes suffer from high cross-shard transaction processing latency, low parallelism, incomplete cross-shard views of shard members, centralized reconfiguration, high overhead of randomness generation, and lack of formalized protocol design and security proofs. This paper proposes a flexible sharding (FS) blockchain protocol. First, a cross-shard Byzantine fault tolerance (CSBFT) protocol is designed to cut down confirmation delays when processing cross-shard transactions. Second, we utilize multiple parallel CSBFT where each node acts not only as a leader but also as multiple ordinary members to break through the performance bottleneck caused by a leader’s bandwidth and computing power, improving the system parallelism. Third, a cross-shard transaction censorship attack is proposed, and a cross-shard view-change mechanism is designed to defend against it. Fourth, a secure and truly decentralized shard reconfiguration method combining proof-of-work, proof-of-possession, and intra-shard BFT is designed. Fifth, we utilize a formal protocol design method and give strict security proof for each protocol. Finally, we evaluate FS from both theoretical and practical perspectives. FS is proven to have lower communication and computation complexity and achieve considerable performance.

TSBFT: A scalable and efficient leaderless byzantine consensus for consortium blockchain

In this paper, we present a high-performance, scalable Byzantine fault tolerance (BFT) protocol TSBFT for the consortium blockchains that does not rely on expensive leader-driven communication. It overcomes the challenges faced by the existing BFT protocol in three aspects: single-point failure, huge total message sizes, and limited by the slowest nodes. The proposed protocol secretly selects block proposers and uses threshold signature as a multi-round voting mechanism to confirm the validity of the proposed block. We adopt transmission pipelining to improve the network utilization while optimizing the gossip communication scheme to reduce the total message sizes. Finally, our protocol guarantees the security and liveness of the system. Experimental results show that, compared with other related BFT protocols (e.g., PBFT), TSBFT can effectively solve these three challenges. In addition, our experiments also show how the different optimization ingredients of TSBFT contribute to its performance and scalability. The results show that compared with the traditional BFT protocol, it can scale from dozens of nodes to hundreds of nodes.

Votes-as-a-Proof (VaaP): Permissioned Blockchain Consensus Protocol Made Simple

With the development of Blockchain technology, permissioned Blockchains are getting more and more attention from researchers because applications based on permissioned Blockchains are more practical and easier to be carried out. This paper aims to design a dedicated consensus protocol for permissioned Blockchains. The existing consensus protocols applied to permissioned Blockchains are either derived from public Blockchains such as Proof of Work (PoW) or Proof of Stake (PoS), with full decentralization, resulting in low transaction processing efficiency; or derived from traditional Byzantine fault-tolerant (BFT) consensus protocols such as Practical BFT (PBFT) or HoneyBadgerBFT, with high communication complexity of the consensus process, resulting in low scalability. Therefore, we propose a dedicated consensus protocol for permissioned Blockchains called Votes-as-a-Proof (VaaP) with high transaction processing efficiency while ensuring high scalability. Every node in VaaP runs a simple consensus process based on voting in parallel. Faulty nodes will only deprive themselves of using consensus service. We present the comparison of VaaP and Sphinx, one of the state-of-the-art consensus protocols, analytically and experimentally (up to 500 nodes). The results indicate that VaaP outperforms Sphinx in throughput, latency and scalability.

Flexico: An efficient dual-mode consensus protocol for blockchain networks.

Blockchain is a Byzantine fault tolerant (BFT) system wherein decentralized nodes execute consensus protocols to drive the agreement process on new blocks added to a distributed ledger. Generally, two-round communications among [Formula: see text] nodes are required to tolerate up to [Formula: see text] faults in BFT-based consensus networks. This communication pattern corresponds to the worse-case scenario of consensus achievement, even under asynchronous network conditions. Nevertheless, it is not uncommon for a network to operate under better conditions, where a consensus can be reached with a lower communication cost. Hence, with the addition of a faster optimistic path toward an agreement, the idea of dual-mode consensus has been proposed as a promising approach to enhance the performance of asynchronous BFT protocols. However, this opportunity is not completely exploited by existing dual-mode protocols as the fast path can be followed only in a nonfaulty and synchronous network. This article presents a novel dual-mode protocol consisting of fast and backup subprotocols. To create different consensus committees for fast and backup-mode operations, the network contains both active and passive nodes. A consensus can be expedited through a fast-mode operation when majority of the active nodes can communicate synchronously. Under non-ideal conditions, the backup protocol takes over the agreement process from its fast-mode counterpart without starting over the suspended round. The safety and liveness of the proposed protocol are guaranteed with lower communication costs, which balance the trade-off between protocol efficiency and availability.

Multiaccess Edge Integrated Networking for Internet of Vehicles: A Blockchain-Based Deep Compressed Cooperative Learning Approach

Recently, Internet of Vehicles (IoV) and Machine Learning (ML) have attracted more and more attention. Considering inefficient real-time training and high requirements on computing capabilities of centralized data collection, performing Distributed Machine Learning (DML) in IoV has become an important research branch. However, the heterogeneity, mobility, and distrust among IoV nodes affect how to execute DML effectively, securely, and in a salable manner. In this paper, a blockchain-based Cooperative Learning framework combined with a Deep Compression method (CLDC) is proposed. First, we improve the local training efficiency of lightweight IoV nodes by using deep compression method. Meanwhile, we have introduced a blockchain system in CLDC, the significance of which is that we have completed the transformation from centralized architecture to distributed framework through the blockchain, and shared local training results in a verifiable manner. The framework uses non-tamperable features of the blockchain to ensure the security of local training results. Moreover, we propose a Learning-based Redundant Byzantine Fault Tolerance (L-RBFT) protocol, in which the primary node needs to confirm the loss percentage of learning in the transaction before forwarding the RBFT messages. The significance of L-RBFT is to ensure that IoV nodes obtain the best training results through the consensus of blockchain nodes. We use it to solve the computing and communication resource allocation problem in IoV to clarify the operating mechanism of the proposed framework. The experimental results prove that this scheme performs better when compared with the traditional centralized deep reinforcement learning method.

LWSBFT: Leaderless weakly synchronous BFT protocol

Asynchronous or partially synchronous Byzantine fault-tolerant (BFT) protocols can tolerate up to one-third Byzantine faults, while synchronous Byzantine fault-tolerant protocols can tolerate up to one-half Byzantine faults. The existing synchronous Byzantine fault-tolerant protocols are leader-based protocols, which may lead to unbalanced load between nodes, and constitute a bottleneck that influences the performance of the whole system. In addition, the synchronous BFT protocols rely on a strong assumption: every message sent by an honest node will arrive at its destination within a known bounded time. In this work, in order to obtain better fairness and allow some degree of asynchrony while tolerating one-half faults, we designed LWSBFT, a leaderless BFT protocol in a weakly synchronous model where the synchronous assumption does not have to hold for all nodes all the time. The leaderless BFT protocol is comprised of the weakly synchronous Byzantine reliable broadcast (RBC) protocol and the weakly synchronous binary Byzantine agreement (BA) protocol, both of which can tolerate one-half faults. The weakly synchronous RBC protocol is used by each node to propose its input, and the weakly synchronous binary BA protocol is used to make a decision for each proposed value. The proposed leaderless BFT protocol can ensure both safety and liveness in a weakly synchronous model. We implement our consensus mechanism in Go, and evaluate the proposed consensus mechanism’s performance in terms of throughput and latency.

Byzantine Fault Tolerance For Distributed Ledgers Revisited

The problem of Byzantine Fault Tolerance (BFT) has received a lot of attention in the last 30 years. Due to the popularity of Proof of Stake (PoS) blockchains in recent years, several BFT protocols have been deployed in the large scale of Internet environment. We analyze several popular BFT protocols such as Capser FFG/CBC-FBC for Ethereum 2.0 and GRANDPA for Polkadot. Our analysis shows that the security models for these BFT protocols are slightly different from the models commonly accepted in the academic literature. For example, we show that, if the adversary has a full control of the message delivery order in the underlying network, then none of the BFT protocols for Ethereum blockchain 2.0 and Polkadot blockchain could achieve liveness even in a synchronized network. Though it is not clear whether a practical adversary could actually control and re-order the underlying message delivery system (at Internet scale) to mount these attacks, it raises an interesting question on security model gaps between academic BFT protocols and deployed BFT protocols in the Internet scale. With these analysis, this article proposes a Casper CBC-FBC style binary BFT protocol and shows its security in the traditional academic security model with complete asynchronous networks. For partial synchronous networks, we propose a multi-value BFT protocol BDLS based on the seminal DLS protocol and show that it is one of the most efficient practical BFT protocols at large scale networks in the traditional academic BFT security model. The implementation of BDLS is available at https://github.com/yonggewang/bdls . Finally, we propose a multi-value BFT protocol XP for complete asynchronous networks and show its security in the traditional academic BFT security model.

DBFT: A Byzantine Fault Tolerance Protocol With Graceful Performance Degradation

Byzantine Fault Tolerant (BFT) state machine replication protocols are used to achieve agreement among replicated servers with arbitrary faults. Most existing BFT protocols perform well in fault-free cases, but usually suffer from serious performance degradation when faults occur. In this paper, we present DBFT, a BFT protocol that realizes graceful performance degradation in faulty cases. The major novelty of DBFT lies in the double-response mechanism, which lets replica nodes deterministically respond to clients twice: one is after the speculative execution phase and the other is after the commitment phase. The double-response mechanism ensures good performance in spite of inconsistency in speculative execution. Also, to further alleviates undetectable performance attacks by a smartly malicious primary, we change primary upon every outstanding request. Moreover, DBFT does not involve clients in critical consensus operations so as to reduce the load of clients. We prove the correctness properties, i.e., safety and liveness, of DBFT. We conduct extensive experiments and the results show that, DBFT outperforms similar BFT protocols obviously in normal cases.