Byzantine Fault-tolerant Replication Research Articles

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.

MITRA

Replication is often considered a cost-effective solution for building dependable systems with off-the-shelf hardware. Replication software is usually designed to tolerate crash faults, but Byzantine (or arbitrary) faults such as software bugs are well-known to affect transactional database management systems (DBMSs) as many other classes of software. Despite the maturity of replication technology, Byzantine fault-tolerant replication of databases remains a challenging problem. The paper presents MITRA, a middleware for replicating DBMSs and making them tolerant to Byzantine faults. MITRA is designed to offer transparent replication of off-theshelf DBMSs with replicas from different vendors.

Efficient Randomized Byzantine Fault-Tolerant Replication Based on Special Valued Coin Tossing

Efficient Randomized Byzantine Fault-Tolerant Replication Based on Special Valued Coin Tossing

Adaptive request batching for byzantine replication

Castro and Liskov proposed in 1999 a successful solution for byzantine fault-tolerant replication, named PBFT, which overcame performance drawbacks of earlier byzantine faulttolerant replication protocols. Other proposals extended PBFT with further optimizations, improving PBFT performance in certain conditions. One of the key optimizations of PBFT-based protocols is the use a request batching mechanism. If the target distributed system is dynamic, that is, if its underlying characteristics change dynamically, such as workload, channel QoS, network topology, etc., the configuration of the request batching mechanism must follow the dynamics of the system or it may not yield the desired performance improvement. This paper addresses this challenge by proposing an innovative solution to the dynamic configuration of request batching parameters inspired on feedback control theory. In order to evaluate its efficiency, the proposed solution is simulated in various scenarios and compared with the original version used in the PBFT-family protocols.

Prime: Byzantine Replication under Attack

Existing Byzantine-resilient replication protocols satisfy two standard correctness criteria, safety and liveness, even in the presence of Byzantine faults. The runtime performance of these protocols is most commonly assessed in the absence of processor faults and is usually good in that case. However, faulty processors can significantly degrade the performance of some protocols, limiting their practical utility in adversarial environments. This paper demonstrates the extent of performance degradation possible in some existing protocols that do satisfy liveness and that do perform well absent Byzantine faults. We propose a new performance-oriented correctness criterion that requires a consistent level of performance, even with Byzantine faults. We present a new Byzantine fault-tolerant replication protocol that meets the new correctness criterion and evaluate its performance in fault-free executions and when under attack.

Steward: Scaling Byzantine Fault-Tolerant Replication to Wide Area Networks

This paper presents the first hierarchical byzantine fault-tolerant replication architecture suitable to systems that span multiple wide-area sites. The architecture confines the effects of any malicious replica to its local site, reduces message complexity of wide-area communication, and allows read-only queries to be performed locally within a site for the price of additional standard hardware. We present proofs that our algorithm provides safety and liveness properties. A prototype implementation is evaluated over several network topologies and is compared with a flat byzantine fault-tolerant approach. The experimental results show considerable improvement over flat byzantine replication algorithms, bringing the performance of byzantine replication closer to existing benign fault-tolerant replication techniques over wide area networks.

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.

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.

DepSpace

The tuple space coordination model is one of the most interesting coordination models for open distributed systems due to its space and time decoupling and its synchronization power. Several works have tried to improve the dependability of tuple spaces through the use of replication for fault tolerance and access control for security. However, many practical applications in the Internet require both fault tolerance and security. This paper describes the design and implementation of DepSpace, a Byzantine fault-tolerant coordination service that provides a tuple space abstraction. The service offered by DepSpace is secure, reliable and available as long as less than a third of service replicas are faulty. Moreover, the content-addressable confidentiality scheme developed for DepSpace bridges the gap between Byzantine fault-tolerant replication and confidentiality of replicated data and can be used in other systems that store critical data.