Byzantine Fault-tolerant Systems Research Articles

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.

Availability evaluation of IoT systems with Byzantine fault-tolerance for mission-critical applications

Byzantine fault-tolerant (BFT) systems are able to maintain the availability and integrity of IoT systems, in the presence of failure of individual components, random data corruption or malicious attacks. Fault-tolerant systems in general are essential in assuring continuity of service for mission-critical applications. However, their implementation may be challenging and expensive. In this study, IoT Systems with BFT are considered. Analytical models and solutions are presented as well as a detailed analysis for the evaluation of the availability. BFT is particularly important for blockchain mechanisms, and in turn for IoT, since it can provide a secure, reliable and decentralized infrastructure for IoT devices to communicate and transact with each other. A continuous-time Markov chain is used to model the IoT systems with BFT where the breakdown and repair times follow exponential distributions, and the number of the Byzantine nodes in the network follows various distributions. The presented numerical findings demonstrate the relationship between the number of nodes in the system, the proportion of honest users, and the overall availability. Based on the model, it can be inferred that the correlation between the scale of the system (nodes) and network availability is non-linear. Additionally, results show that even for relatively small-size systems with 40 nodes, an average availability greater than 0.999 and an estimated downtime per year that is less than 9 h is possible.

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.

An Innovative Methodology for Network Latency Detection Based on IoT Centered Blockchain Transactions

The new IoT apps will not be able to inspire people to utilize them and may ultimately lose all their potential if an interoperable and trustworthy ecosystem is not provided. IoT has its extra security difficulties such as information storage, administration, privacy concerns, and authentication. The presently deployed IoT apps have encountered various security and privacy assaults globally. Due to being less secure and low powered, the IoT devices present a simple entryway to the adversaries to obtain access to the corporate networks, leading to giving easy control over all of the data of the users. The objective of this doctorate proposed work will be to solve the security associated difficulties in multiple IoT domains like the e-commerce, vehicular ad hoc networks (VANET), mobile ad hoc networks (MANET), and Internet of Drones (IoD). The proposed study focuses on the development of a distributed framework for IoT based on blockchain. The framework includes the usage of Ethereum-based smart contracts and auction models to increase the income and QoS for both the seller and the buyer and the development of a DAG chain-based distributed framework for parking lot allocation in a network of automobiles. The suggested model includes the requirement of obtaining agreement among the nodes with probability one in such a circumstance. The suggested model demonstrates to be predictable as typical voting-based consensus protocols like Practical Byzantine Fault Tolerance (PBFT) and at the same time can accommodate a high number of nodes even in an asynchronous setting. Research on Byzantine fault-tolerant systems has been ongoing for more than four decades, and although the solutions were shown to be feasible early on, they remained unworkable for a long time. With PBFT, the first feasible solution was provided in 1999, and this sparked fresh research that has resulted in unique applications that are still being developed today employing this technology. Despite the fact that the safety and liveness properties of PBFT-type protocols have been thoroughly investigated, when it comes to practical performance, only empirical results—often obtained in artificial environments—are known, and imperfections in the communication channels are not explicitly considered. It is our goal in this paper to propose the first performance model for PBFT that takes into account the effect of unreliable channels as well as the usage of alternative transport protocols across those channels. We also performed a large number of simulations to test the model and acquire a better understanding of the influence of different deployment factors on the total transaction timeframe.

BFT in Blockchains: From Protocols to Use Cases

A blockchain is a distributed system that achieves strong security guarantees in storing, managing, and processing data. All blockchains achieve a common goal: building a decentralized system that provides a trustworthy service in an untrustworthy environment. A blockchain builds a Byzantine fault-tolerant (BFT) system in which decentralized nodes run a protocol to reach an agreement on the common system state. In this article, we focus on the research of BFT protocols. In particular, we categorize BFT protocols according to both the system models and workflow. We seek to answer these important questions: How has the research in BFT evolved in the past four decades, especially with the rise of blockchains? What are the driven needs for BFT research in the future?

Byzantine Fault-tolerant State-machine Replication from a Systems Perspective

Byzantine fault-tolerant (BFT) state-machine replication makes it possible to design systems that are resilient against arbitrary faults, a requirement considered crucial for an increasing number of use cases such as permissioned blockchains, firewalls, and SCADA systems. Unfortunately, the strong fault-tolerance guarantees provided by BFT replication protocols come at the cost of a high complexity, which is why it is inherently difficult to correctly implement BFT systems in practice. This is all the more true with regard to the plethora of solutions and ideas that have been developed in recent years to improve performance, availability, or resource efficiency. This survey aims at facilitating the task of building BFT systems by presenting an overview of state-of-the-art techniques and analyzing their practical implications, for example, with respect to applicability and composability. In particular, this includes problems that arise in the context of concrete implementations, but which are often times passed over in literature. Starting with an in-depth discussion of the most important architectural building blocks of a BFT system (i.e., clients, agreement protocol, execution stage), the survey then focuses on selected approaches and mechanisms addressing specific tasks such as checkpointing and recovery.

CSMCSM

Many MANET research works are based on the popular informal definition that MANET is a wireless ad-hoc network that has neither infrastructure nor backbone and every network node is autonomous and moves depending on its mobility. Unfortunately, this definition pays no attention to the network servers that are essential in core-based, mission-critical, and military MANETs. In core-based MANETs, external intrusion detection systems (IDS) cannot detect internal Byzantine attacks; in addition, internal Byzantine fault tolerant (BFT) systems are unqualified to detect typical external wireless attack. Therefore, there is a real need to combine both internal and external mobile ad-hoc network (MANET) ID systems. Here, CSMCSM is presented as a two-level client server model for comprehensive security in MANETs that integrates internal and external attack detectors in one device. The internal component is based on a BFT consensus algorithm while the external component employs decision tree to classify the MANET attacks.

Scaling Membership of Byzantine Consensus

Scaling Byzantine Fault Tolerant (BFT) systems in terms of membership is important for secure applications with large participation such as blockchains. While traditional protocols have low latency, they cannot handle many processors. Conversely, blockchains often have hundreds to thousands of processors to increase robustness, but they typically have high latency or energy costs. We describe various sources of unscalability in BFT consensus protocols. To improve performance, many BFT protocols optimize the “normal case,” where there are no failures. This can be done in a modular fashion by wrapping existing BFT protocols with a building block that we call alliance . In normal case executions, alliance can scalably determine if the initial conditions of a BFT consensus protocol predetermine the outcome, obviating running the consensus protocol. We give examples of existing protocols that solve alliance. We show that a solution based on hypercubes and MAC s has desirable scalability and performance in normal case executions, with only a modest overhead otherwise. We provide important optimizations. Finally, we evaluate our solution using the ns3 simulator and show that it scales up to thousands of processors and compare with prior work in various network topologies.

Implementing a blockchain-based local energy market: Insights on communication and scalability

Peer-to-peer (P2P) energy markets are gaining interest in the energy sector as a means to increase the share of decentralised energy resources (DER), thus fostering a clean, resilient and decentralised supply of energy. Various reports have touted P2P energy markets as ideal use case for blockchain-technology, as it offers advantages such as fault-tolerant operation, trust delegation, immutability, transparency, resilience, and automation. However, relatively little is known about the influence of hardware and communication infrastructure limitations on blockchain systems in real-life applications. In this article, we demonstrate the implementation of a real-world blockchain managed microgrid in Walenstadt, Switzerland. The 37 participating households are equipped with 75 special smart-metres that include single board computers (SBC) that run their own, application-specific private blockchain. Using the field-test setup, we provide an empirical evaluation of the feasibility of a Byzantine fault tolerant blockchain system. Furthermore, we artificially throttle bandwidth between nodes to simulate how the bandwidth of communication infrastructure impacts its performance. We find that communication networks with a bandwidth smaller than 1000 kbit/s – which includes WPAN, LoRa, narrowband IoT, and narrowband PLC – lead to insufficient throughput of the operation of a blockchain-managed microgrid. While larger numbers of validators may provide higher decentralisation and fault-tolerant operation, they considerably reduce throughput. The results from the field-test in the Walenstadt microgrid show that the blockchain running on the smart-metre SBCs can provide a maximum throughput of 10 transactions per second. The blockchain throughput halts almost entirely if the system is run by more than 40 validators. Based on the field test, we provide simplified guidelines for utilities or grid operators interested in implementing local P2P markets based on BFT systems.

Scalable Byzantine fault-tolerant state-machine replication on heterogeneous servers

When provided with more powerful or extra hardware, state-of-the-art Byzantine fault-tolerant (BFT) replication protocols are unable to effectively exploit the additional computing resources: on the one hand, in settings with heterogeneous servers existing protocols cannot fully utilize servers with higher performance capabilities. On the other hand, using more servers than the minimum number of replicas required for Byzantine fault tolerance in general does not lead to improved throughput and latency, but instead actually degrades performance. In this paper, we address these problems with Omada, a BFT system architecture that is able to benefit from additional hardware resources. To achieve this property while still providing strong consistency, Omada first parallelizes agreement into multiple groups and then executes the requests handled by different groups in a deterministic order. By varying the number of requests to be ordered between groups as well as the number of groups that a replica participates in between servers, Omada offers the possibility to individually adjust the resource usage per server. Moreover, the fact that not all replicas need to take part in every group enables the architecture to exploit additional servers.

From Byzantine Fault-Tolerance to Fault-Avoidance: An Architectural Transformation to Attack and Failure Resiliency

We present Byzantine Fault-Avoidance (BFA), a fault-resilient architecture designed for Byzantine Fault Tolerant (BFT) systems to withstand against attacks and failures. BFA allows replicas to short live on a given computing platform, i.e., hardware, hypervisors and OS, to thwart successful and in-progress attacks while simultaneously preserving the correctness condition of BFT properties; safety and liveness . BFA combines the cloud management software stack of OpenStack ( nova) and the Software Defined Network (SDN) implementation (neutron) to control the replicas susceptibility window of attack in order to avoid Byzantine faults. The proposed fault-avoidance scheme illustrates the defensive security solutions enabled by the underlying cloud computing fabric are far superior than the ones implemented at the application/protocol level. Preliminary results of widely studied BFT system ( BFT-SMaRT ) deployed in a cloud infrastructure ( OpenStack-Kilo ) indicate that BFA achieves desired BFT reliability properties and throughput over contested environments.

Resource-Efficient Byzantine Fault Tolerance

One of the main reasons why Byzantine fault-tolerant (BFT) systems are currently not widely used lies in their high resource consumption: <inline-formula><tex-math notation="LaTeX">$3f+1$</tex-math></inline-formula> replicas are required to tolerate only <inline-formula><tex-math notation="LaTeX">$f$</tex-math></inline-formula> faults. Recent works have been able to reduce the minimum number of replicas to <inline-formula><tex-math notation="LaTeX">$2f+1$</tex-math> </inline-formula> by relying on trusted subsystems that prevent a faulty replica from making conflicting statements to other replicas without being detected. Nevertheless, having been designed with the focus on fault handling, during normal-case operation these systems still use more resources than actually necessary to make progress in the absence of faults. This paper presents <i>Resource-efficient Byzantine Fault Tolerance</i> ( <small>ReBFT</small> ), an approach that minimizes the resource usage of a BFT system during normal-case operation by keeping <inline-formula> <tex-math notation="LaTeX">$f$</tex-math></inline-formula> replicas in a passive mode. In contrast to active replicas, passive replicas neither participate in the agreement protocol nor execute client requests; instead, they are brought up to speed by verified state updates provided by active replicas. In case of suspected or detected faults, passive replicas are activated in a consistent manner. To underline the flexibility of our approach, we apply <small>ReBFT</small> to two existing BFT systems: PBFT and MinBFT.

Zyzzyva

A longstanding vision in distributed systems is to build reliable systems from unreliable components. An enticing formulation of this vision is Byzantine Fault-Tolerant (BFT) state machine replication, in which a group of servers collectively act as a correct server even if some of the servers misbehave or malfunction in arbitrary (“Byzantine”) ways. Despite this promise, practitioners hesitate to deploy BFT systems, at least partly because of the perception that BFT must impose high overheads. In this article, we present Zyzzyva, a protocol that uses speculation to reduce the cost of BFT replication. In Zyzzyva, replicas reply to a client's request without first running an expensive three-phase commit protocol to agree on the order to process requests. Instead, they optimistically adopt the order proposed by a primary server, process the request, and reply immediately to the client. If the primary is faulty, replicas can become temporarily inconsistent with one another, but clients detect inconsistencies, help correct replicas converge on a single total ordering of requests, and only rely on responses that are consistent with this total order. This approach allows Zyzzyva to reduce replication overheads to near their theoretical minima and to achieve throughputs of tens of thousands of requests per second, making BFT replication practical for a broad range of demanding services.

Proactive service migration for long-running Byzantine fault-tolerant systems

A proactive recovery scheme based on service migration for long-running Byzantine fault-tolerant systems is described. Proactive recovery is an essential method for ensuring the long-term reliability of fault-tolerant systems that are under continuous threats from malicious adversaries. The primary benefit of our proactive recovery scheme is a reduced vulnerability window under normal operation. This is achieved in two ways. First, the time-consuming reboot step is removed from the critical path of proactive recovery. Second, the response time and the service migration latency are continuously profiled and an optimal service migration interval is dynamically determined during runtime based on the observed system load and the user-specified availability requirement.

Zyzzyva

A longstanding vision in distributed systems is to build reliable systems from unreliable components. An enticing formulation of this vision is Byzantine fault-tolerant (BFT) state machine replication, in which a group of servers collectively act as a correct server even if some of the servers misbehave or malfunction in arbitrary (Byzantine) ways. Despite this promise, practitioners hesitate to deploy BFT systems at least partly because of the perception that BFT must impose high overheads. In this article, we present Zyzzyva, a protocol that uses speculation to reduce the cost of BFT replication. In Zyzzyva, replicas reply to a client's request without first running an expensive three-phase commit protocol to agree on the order to process requests. Instead, they optimistically adopt the order proposed by a primary server, process the request, and reply immediately to the client. If the primary is faulty, replicas can become temporarily inconsistent with one another, but clients detect inconsistencies, help correct replicas converge on a single total ordering of requests, and only rely on responses that are consistent with this total order. This approach allows Zyzzyva to reduce replication overheads to near their theoretical minima and to achieve throughputs of tens of thousands of requests per second, making BFT replication practical for a broad range of demanding services.

Separating agreement from execution for byzantine fault tolerant services

We describe a new architecture for Byzantine fault tolerant state machine replication that separates agreement that orders requests from execution that processes requests. This separation yields two fundamental and practically significant advantages over previous architectures. First, it reduces replication costs because the new architecture can tolerate faults in up to half of the state machine replicas that execute requests. Previous systems can tolerate faults in at most a third of the combined agreement/state machine replicas. Second, separating agreement from execution allows a general privacy firewall architecture to protect confidentiality through replication. In contrast, replication in previous systems hurts confidentiality because exploiting the weakest replica can be sufficient to compromise the system. We have constructed a prototype and evaluated it running both microbenchmarks and an NFS server. Overall, we find that the architecture adds modest latencies to unreplicated systems and that its performance is competitive with existing Byzantine fault tolerant systems.