Byzantine agreement in the presence of mixed faults on processorsand links

In early stage, the Byzantine agreement (BA) problem was studied with single faults on processors in either a fully connected network or a nonfully connected network. Subsequently, the single fault assumption was extended to mixed faults (also referred to as hybrid fault model) on processors. For the case of both processor and link failures, the problem has been examined in a fully connected network with a single faulty type, namely an arbitrary fault. To release the limitations of a fully connected network and a single faulty type, the problem is reconsidered in a general network. The processors and links in such a network can both be subjected to different types of fault simultaneously. The proposed protocol uses the minimum number of message exchanges and can tolerate the maximum number of allowable faulty components to make each fault-free processor reach an agreement     

Reaching Agreement among Virtual Subnets in Hybrid Failure Mode

Fault-tolerance is an important research topic in the study of distributed systems. To cope with the influence of faulty components, reaching a common agreement in the presence of faults before performing certain tasks is essential. However, the Byzantine Agreement (BA) problem is a fundamental problem in fault-tolerant distributed systems. In previous studies, protocols dealing with the BA problem focused on static networks; however, these do not perform well in dynamically changing mobile networks. The most well known mobile network is the Mobile Ad-hoc Network (MANET). To enhance fault-tolerance and MANET reliability, the BA problem in virtual subnets of MANET is revisited in this paper. The proposed protocol is called the Hybrid Agreement Protocol (HAP). It achieves agreement on a common value among all functional mobile processors in a minimal number of message exchange rounds, and can tolerate a maximal number of allowable faulty components in the virtual subnet of MANET.     

From immediate agreement to eventual agreement: early stopping agreement protocol for dynamic networks with malicious faulty processors

With the rapid advancement of wireless networking technology, networks have evolved from static to dynamic. Reliability of dynamic networks has virtually become an important issue. Fortunately, a solution to the above issue can be derived from solutions to the Byzantine Agreement (BA) problem. BA problem can be solved by protocols that make processors reach an agreement through message exchange. Protocols used to solve the problem can be divided into Immediate Byzantine Agreement (IBA) protocols and Eventual Byzantine Agreement (EBA) protocols. In IBA protocols, the number of rounds of message exchange is determined by the total number of processors in the network. Even if no faulty processor is present in the network, IBA protocols still require a fixed number of rounds of message exchange, causing a waste of time. In contrast, EBA protocols dynamically adjust the number of rounds of message exchange according to the interference of faulty processors. In terms of efficiency, EBA protocols certainly outperform IBA protocols. Due to the fact that the existing EBA protocols have been designed for static networks, they cannot work on dynamic networks. In this paper, we revisit the EBA problem in dynamic networks to increase the reliability of dynamic networks. Simulations will be conducted to validate that the proposed protocol requires the minimum rounds of message exchange and can tolerate the maximum number of malicious faulty processors compared to other existing protocols.     

Visiting Byzantine Agreement underlying Ad Hoc environment

The Mobile Ad Hoc Network (MANET) has become more popular because the MANET is a self-organizing, self-configuring, and an instantly deployable multi-hop wireless network that responds to application needs without any fixed infrastructure. Moreover, the MANET is fault-tolerant and reliable. A mechanism is needed in the MANET that allows a set of nodes to agree on a common value. The distributed Byzantine Agreement (BA) problem is one of the most important issues in designing a fault-tolerant system. In many cases, reaching a common agreement among fault-free nodes in coping with the influence from faulty components is crucial in a fault-tolerant system. When a common agreement is achieved, all fault-free nodes in the system can produce stable results without any influence from the faulty components. In this study, the BA problem is visited in a MANET, in which the components are subject to a malicious fault. The proposed protocol can tolerate the maximum number of allowable faulty nodes using a minimum number of message exchange rounds. Each fault-free node can reach a common agreement value for the BA problem in a MANET. The text was submitted by the authors in English.     

Eventual strong consensus with fault detection in the presence of dual failure mode on processors under dynamic networks

The fault tolerance capability and reliability of a distributed system can be enhanced if the Strong Consensus (SC) problem can be properly addressed. Most of the extant SC protocols are designed for static networks. Besides, the number of rounds of message exchange required by all of the extant SC protocols is determined by the total number of processors in the network rather than by the actual number of faulty processors in the network. Even if there is only a few or no faulty processor in the network, the SC protocols may waste a lot of time and memory space on many unnecessary rounds of message exchange. Thus, this paper revisits the SC problem in dynamic networks and uses two rules, Detection Rule for Malicious fault in dynamic network (DRM_dyn) and Early Stopping Rule for Strong Consensus protocol in dynamic networks (ESRSC_dyn), to reduce the time consumption and space complexity of SC protocols. DRM_dyn is a rule that detects malicious processors, and ESRSC_dyn is a rule that determines whether the messages collected are enough for reaching a strong consensus. To be succinct, the proposed SC protocol can not only work in dynamic networks consisting of both dormant processors and malicious processors (dual failure mode) but also ensure that all correct processors reach a SC value within fewer rounds of message exchange than required by the extant SC protocols.     

Byzantine Agreement in a generalized connected network

Traditionally, the Byzantine Agreement (BA) problem is studied either in a fully connected network or in a broadcast network. A generalized network model for BA is proposed in this paper. A fully-connected network or a broadcast network is a special case of the new network architecture. Under the new generalized network model, the BA problem is reexamined with the assumption of malicious faults on both processors and transmission medium (TM), as opposed to previous studies which consider malicious faults on processors only. The proposed algorithm uses the minimum number of message exchanges, and can tolerate the maximum number of allowable faulty components to make each healthy processor reach a common agreement for the cases of processor failures, TM failures, or processor/TM failures. The results can also be used to solve the interactive consistency problem and the consensus problem     

The optimal generalized Byzantine Agreement in Cluster-based Wireless Sensor Networks

A Wireless Sensor Network (WSN) is a wireless network consisting of spatially distributed autonomous devices using sensor nodes in a wide range of applications in various domains. In the future, WSNs are expected to be integrated into the “Internet of Things” (IoT), where sensor nodes join the Internet dynamically, and use them to collaborate and accomplish their tasks. Because of the communications of WSN will produce a broadcast storm, the Cluster-based Wireless Sensor Network (CWSN) was proposed to ameliorate the broadcast storm. However, the capability of the fault-tolerance and reliability of CWSNs must be carefully investigated and analyzed. To cope with the influence of faulty components, reaching a common agreement in the presence of faults before performing certain tasks is essential. Byzantine Agreement (BA) problem is a fundamental problem in fault-tolerant distributed systems. To enhance fault-tolerance and reliability of CWSN, the BA problem in CWSN is revisited in this paper. In this paper, a new BA protocol is proposed that adapts to the CWSN and derives its limit of allowable faulty components, while maintaining the minimum number of message exchanges.     

The anatomy study of consensus agreement in MANETs

Reliability is an important research topic of distributed systems. To achieve fault-tolerance in the distributed systems, healthy processors need to reach a common agreement before performing certain special tasks, even if faults exist in many circumstances. This problem is called as the Byzantine Agreement (BA) problem and it must be addressed. In general, the traditional BA problem is solved in well-defined networks. However, the MANETs (Mobile Ad-hoc Network) are increasing in popularity and its network topology is dynamic in nature. In this paper, the BA problem is re-examined in MANETs. Our protocol uses the minimum number of message exchanges to reach an agreement within the distributed system while tolerating the maximum number of faulty processors in MANETs.     

A new solution for the Byzantine agreement problem

Reliability is an important research topic in distributed computing systems consisting of a large number of processors. To achieve reliability, the fault-tolerance scheme of the distributed computing system must be revised. This kind of problem is known as a Byzantine agreement (BA) problem. It requires all fault-free processors to agree on a common value, even if some components are corrupt. Consequently, there have been significant studies of this agreement problem in distributed systems. However, the traditional BA protocols focus on running ⌊(n−1)/3⌋+1 rounds of message exchange continuously to make each fault-free processor reach an agreement. In other words, since having a large number of messages results in a large protocol overhead, those protocols are inefficient and unreasonable, especially for some network environments which have large number of processors. In this study, we propose a novel and efficient protocol to reduce the number of messages. Our protocol can collect, compare and replace the received values to find the reliable processors and replace the values sent by the unreliable processors. Subsequently, each processor can agree on a common value through three rounds of message exchange. Furthermore, the proposed protocol can use the minimum number of messages to tolerate the maximum number of faulty components in a distributed system.     

The incremental agreement

To achieve reliable distributed systems, the fault-tolerance must be studied. One of the most important problems of fault-tolerance issues lies in the Byzantine Agreement (BA) problem. The primary issue surrounding BA is that fault-free processors must obtain common agreement even in cases where faults persist. In this field, the fault diagnosis protocol has been proposed so that each fault-free processor detects/locates a common set of faulty processors. However, in this study, the incremental agreement is invoked to make each processor able to agreement upon executing the fault diagnosis protocol using minimal rounds of message exchange in the presence of dual failure characteristics of processors.     

一种基于无效链路的分布式故障诊断一致性协议

故障诊断一致性(fault diagnosis agreement,FDA)是高可靠容错分布式系统的性能和完整性的重要保障.目前,大部分FDA协议还是只考虑单一故障组件的简单网络,而对于实际的分布式应用、故障节点和故障链路并存的系统假设更加有意义.但是,在此假设下,对恶意(拜占庭故障)组件的诊断是不可能满足FDA的.为此,首先提出了一种无效链路(invalid link)故障模型,可以更加准确地描述恶意组件的故障行为对系统的影响,有效提高故障诊断的覆盖率.在此模型基础上,提出了一个基于证据的故障诊断协议--PLFDA,可以同时对恶意节点和恶意链路进行检测和定位,并且能够满足故障诊断一致性要求.     

An optimal solution for byzantine agreement under a hierarchical cluster-oriented mobile ad hoc network

Mobile ad hoc NETworks (MANETs) are becoming more popular due to the advantage that they do not require any fixed infrastructure, and that communication among processors can be established quickly. For this reason, potential MANET applications include military uses, search and rescue and meetings or conferences. Therefore, the fault-tolerance and reliability of the MANET is an important issue, which needs to be considered. The problem of reaching agreement in the distributed system is one of the most important areas of research to design a fault-tolerant system. With an agreement, each correct processor can cope with the influence from other faulty components in the network to provide a reliable solution. In this research, a potential MANET with a dual failure mode is considered. The proposed protocol can use the minimum number of rounds of message exchange to reach a common agreement and can tolerate a maximum number of allowable faulty components to induce all correct processors to reach a common agreement within the MANET.     

Optimal agreement protocol in malicious faulty processors andfaulty links

Traditionally, the problems of Byzantine agreement, consensus, and interactive consistency are studied in a fully connected network with processors in malicious failure only. Such problems are reexamined with the assumption of malicious faults on both processors and links. The proposed protocols use the minimum number of message exchanges and can tolerate the maximum number of allowable faulty components to make each fault-free processor reach a common agreement for the cases of processor failure, link failure, or processor and link failure     

Grouping Byzantine Agreement

The reliability of the distributed system has always been an important topic of research. Byzantine Agreement (BA) protocol, which allows the fault-free processors to agree on a common value, is one of the most fundamental problems studied in a distributed system. In previous works, the problem was visited in a fully connected network or an unfully connected network with fallible processors. In this paper, the BA problem is reexamined in a group-oriented network, which has the feature of grouping, and the network topology does not have to be fully connected. We also enlarge the fault tolerant capability by allowing dormant faults and malicious faults (also called as the dual failure mode) to exist in a group-oriented network simultaneously. The proposed protocol is more efficient than the traditional BA protocols and can tolerate the maximum number of tolerable faulty processors.     

The anatomy study of server-initial agreement for general hierarchy wired/wireless networks

The Byzantine Agreement (BA) plays a key role in fault-tolerant distributed system design. A number of solutions to the BA problem based on various network model assumptions have been proposed. However, most existing BA protocols are designed for pure wired or pure wireless networks. In practice, most current networks are combined wired and wireless environments. In this paper, we extend the BA problem over a combined wired/wireless network, consisting of both powerful computing stationary processor and low-power mobile processor. The communication overhead of BA protocol is inherently large and secure group communications are important. The protocols proposed in this paper use the hierarchical model concept to reduce the communication overhead and provide secure group communications well suited for combined wired/wireless networks.     

安全高效的异构无线网络可控匿名漫游认证协议

分析传统的匿名漫游认证协议,指出其匿名不可控和通信时延较大的不足.针对上述不足,提出异构无线网络可控匿名漫游认证协议,远程网络认证服务器通过1轮消息交互即可完成对移动终端的身份合法性验证,当移动终端发生恶意操作时,家乡网络认证服务器可协助远程网络认证服务器撤销移动终端的身份匿名性.该协议在实现匿名认证的同时,还具有恶意匿名的可控性,有效防止了恶意行为的发生,且其通信时延较小.安全性证明表明,该协议在CK安全模型中是可证安全的.相对于传统漫游机制而言,该协议更适合于异构无线网络.     

A note on consensus on dual failure modes

F.J. Meyer and D.K. Pradhan (1991) proposed the MS (for “mixed-sum”) algorithm to solve the Byzantine Agreement (BA) problem with dual failure modes: arbitrary faults (Byzantine faults) and dormant faults (essentially omission faults and timing faults). Our study indicates that this algorithm uses an inappropriate method to eliminate the effects of dormant faults and that the bound on the number of allowable faulty processors is overestimated. This paper corrects the algorithm and gives a new bound for the allowable faulty processors     

A distributed fault identification protocol for wireless and mobile ad hoc networks

This paper considers the problem of self-diagnosis of wireless and mobile ad hoc networks (MANETs) using the comparison approach. In this approach, a network (MANET) consists of a collection of n   independent heterogeneous mobile or stationary hosts interconnected via wireless links, and it is assumed that at most σ$\sigma$ of these hosts are faulty. In order to diagnose the state of the MANET, tasks are assigned to pairs of hosts and the outcomes of these tasks are compared. The agreements and disagreements between the hosts are the basis for identifying the faulty ones. The comparison approach is believed to be one of the most practical fault identification approaches for diagnosing hard and soft faults. We develop a new distributed self-diagnosis protocol, called Dynamic-DSDP, for MANETs that identifies both hard and soft faults in a finite amount of time. The protocol is constructed on top of a reliable multi-hop architecture. Correctness and complexity proofs are provided and they show that our Dynamic-DSDP performs better, from a communication complexity viewpoint, than the existing protocols. We have also developed a simulator, that is scalable to a large number of nodes. Using the simulator, we carried out a simulation study to analyze the effectiveness of the self-diagnosis protocol and its performance with regards to the number of faulty hosts. The simulation results show that the proposed approach is an attractive and viable alternative or addition to present fault diagnosis techniques in MANET environments.     

An anonymous distributed routing protocol in mobile ad-hoc networks

This paper proposes an efficient anonymous routing protocol for mobile ad hoc networks (MANETs). This protocol considers symmetric and asymmetric links during the wireless communication of MANETs. A MANET is one type of self-organized wireless network that can be formed by several wireless devices such as laptops, tablet PCs, and smartphones. Different wireless transmission ranges of different mobile devices lead to a special communication condition called an asymmetric link. Most research on this topic focuses on providing security and anonymity for the symmetric link without considering the asymmetric link. This paper proposes a novel distributed routing protocol beyond the symmetric and asymmetric links. This protocol guarantees the security, anonymity, and high reliability of an established route by avoiding unreliable intermediate nodes. The routes generated by the proposed protocol are shorter than previous research. The proposed protocol enhances MANET performance in assuring security and anonymity.