Identity-based fault-tolerant conference key agreement

Lots of conference key agreement protocols have been suggested to secure computer network conference. Most of them operate only when all conferees are honest, but do not work when some conferees are malicious and attempt to delay or destruct the conference. Recently, Tzeng proposed a conference key agreement protocol with fault tolerance in terms that a common secret conference key among honest conferees can be established even if malicious conferees exist. In the case where a conferee can broadcast different messages in different subnetworks, Tzeng's protocol is vulnerable to a "different key attack" from malicious conferees. In addition, Tzeng's protocol requires each conferee to broadcast to the rest of the group and receive n - 1 message in a single round (where n stands for the number of conferees). Moreover, it has to handle n simultaneous broadcasts in one round. In this paper, we propose a fault-tolerant conference key agreement protocol, in which each conferee only needs to send one message to a "semitrusted" conference bridge and receive one broadcast message. Our protocol is an identity-based key agreement, built on elliptic curve cryptography. It is resistant to the different key attack from malicious conferees and needs less communication cost than Tzeng's protocol.     

A protocol to achieve independence in constant rounds

Independence is a fundamental property needed to achieve security in fault-tolerant distributed computing. In practice, distributed communication networks are neither fully synchronous or fully asynchronous, but rather loosely synchronized. By this, we mean that in a communication protocol, messages at a given round may depend on messages from other players at the same round. These possible dependencies among messages create problems if we need n players to announce independently chosen values. This task is called simultaneous broadcast. In this paper, we present the first constant round protocol for simultaneous broadcast in a reasonable computation model (which includes a common shared random string among the players). The protocol is provably secure under general cryptographic assumptions. In the process, we develop a new and stronger formal definition for this problem. Previously known protocols for this task required either O(log n) or expected constant rounds to complete (depending on the computation model considered)     

A fault-tolerant protocol for atomic broadcast

A general protocol for atomic broadcast in networks is presented. The protocol tolerates loss, duplication, reordering, delay of messages, and network partitioning in an arbitrary network of fail-stop sites (i.e. no Byzantine site behavior is tolerated). The protocol is based on majority-concensus decisions to commit on unique ordering of received broadcast messages. Under normal operating conditions, the protocol requires three phases to complete and approximately 4N/V messages where N is the number of sites. This overhead is distributed among the messages of which the delivery decision is made and the heavier the broadcast message traffic, the lower the overhead per broadcast message becomes. Under abnormal operating conditions, a decentralized termination protocol (also presented) is invoked. A performance analysis of this protocol is presented, showing that this protocol commits with high probability under realistic operating conditions without invoking termination protocol if N is sufficiently large. The protocol retains its efficiency in wide-area networks where broadcast communication media are unavailable     

Processor membership in asynchronous distributed systems

Presents protocols for determining processor membership in asynchronous distributed systems that are subject to processor and communication faults. These protocols depend on the placement of a total order on broadcast messages. The types of systems for which each of these protocols is applicable are characterized by the properties of the communication mechanisms and by the availability of stable storage. In the absence of stable storage or of a mechanism for distinguishing promptly delivered messages, the authors show that no membership protocol can exist. They also discuss their experience in implementing these membership protocols     

Enhancing group communication with self-manageable behavior

Group communication protocols (GCPs) play an important role in the design of modern distributed systems. A typical GCP exchanges control messages to provide message delivery guarantees, and a key point in the configuration of such a protocol is to establish the right trade-off between message overhead and delivery latency. This trade-off becomes even a greater challenge in systems where computing resources and application requirements may change at runtime. In such scenarios, the configuration of a GCP must be continuously re-adjusted to attain certain performance goals, or to adapt to current resource availability. This paper addresses this challenge by proposing self-managing mechanisms based on feedback control theory to a GCP especially designed to be self-manageable; in the proposed protocol, message overhead and delivery latency can be adjusted at runtime to follow some new operating set-point. The evaluation performed under varied scenarios shows the effectiveness of our approach.     

Adaptive broadcast by fault-tolerant spanning tree switching

Adaptation is a desirable requirement in a distributed system as it helps the system to perform efficiently under different environments. For many problems, more than one protocol exists, such that one protocol performs better in one environment while the other performs better in another. In such cases, adaptive distributed systems can be designed by dynamically switching between the protocols as the environment changes. Distributed protocol switching is also important for performance enhancement, or fault-tolerance of a distributed system. In this work, we illustrate distributed protocol switching by providing a distributed algorithm for adaptive broadcast that dynamically switches from a BFS tree to a DFS tree. The proposed switching algorithm can also handle arbitrary crash failures. It ensures that switching eventually terminates in spite of failures and the desired tree (DFS tree) results as the output. We also investigate the properties that can be guaranteed on the delivery of broadcast messages under specific failure conditions. We show that under no failure, each broadcast message is eventually correctly delivered to all the nodes in spite of switching. Under arbitrary crash fault, we ensure that switching eventually terminates with the desired tree as the broadcast topology. We also investigate the specific delivery guarantees that can be provided when a single crash fault happens, both during switching and when no switching is in progress.     

Using optimistic atomic broadcast in transaction processing systems

Atomic broadcast primitives are often proposed as a mechanism to allow fault-tolerant cooperation between sites in a distributed system. Unfortunately, the delay incurred before a message can be delivered makes it difficult to implement high performance, scalable applications on top of atomic broadcast primitives. Recently, a new approach has been proposed for atomic broadcast which, based on optimistic assumptions about the communication system, reduces the average delay for message delivery to the application. We develop this idea further and show how applications can take even more advantage of the optimistic assumption by overlapping the coordination phase of the atomic broadcast algorithm with the processing of delivered messages. In particular, we present a replicated database architecture that employs the new atomic broadcast primitive in such a way that communication and transaction processing are fully overlapped, providing high performance without relaxing transaction correctness.     

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.     

基于服务器转发的支持多种通信方式的通信协议

提出了一种基于服务器转发的通信协议，其能够支持广播、组播、单播这几种通信方式，支持多种类型消息的通信。介绍了该协议的功能、报文格式以及实现方法。     

Complexity of distributed commit protocols

Summary Implementation of atomic actions in a distributed system in the presence of fail-stop failures is investigated. Worst case time and message complexities of the protocols realizing this are studied on complete graphs, rings, trees, and arbitrary graphs. Two modes of communication are considered — point-to-point and broadcast. Individual lower and upper bounds on time and messages are presented and the simultaneous achievability of the optimum message and time bounds is shown impossible in all the interesting cases.     

Centralized asynchronous broadcast in radio networks

We study asynchronous broadcasting in packet radio networks. A radio network is represented by a directed graph, in which one distinguished source node stores a message that needs to be disseminated among all the remaining nodes. An asynchronous execution of a protocol is a sequence of events, each consisting of simultaneous deliveries of messages. The correctness of protocols is considered for specific adversarial models defined by restrictions on events the adversary may schedule. A protocol specifies how many times the source message is to be retransmitted by each node. The total number of transmissions over all the nodes is called the work of the broadcast protocol; it is used as complexity measure. We study computational problems, to be solved by deterministic centralized algorithms, either to find a broadcast protocol or to verify the correctness of a protocol, for a given network. The amount of work necessary to make a protocol correct may have to be exponential in the size of network. There is a polynomial-time algorithm to find a broadcast protocol for a given network. We show that certain problems about broadcasting protocols for given networks are complete in NP and co-NP complexity classes.     

An Adaptive Causal Ordering Algorithm Suited to Mobile Computing Environments

Causal message ordering is required for several distributed applications. In order to preserve causal ordering, only direct dependency information between messages, with respect to the destination process(es), need be sent with each message. By eliminating other kinds of control information from the messages, the communication overheads can be significantly reduced. In this paper we present an algorithm that uses this knowledge to efficiently enforce causal ordering of messages. The proposed algorithm does not require any prior knowledge of the network topology or communication pattern. As computation proceeds, it acquires knowledge of the communication pattern and is capable of handling dynamically changing multicast communication groups, and minimizing the communication overheads. With regard to communication overheads, the algorithm is optimal for the broadcast communication case. Extensive simulation experiments demonstrate that the algorithm imposes lower communication overheads than previous causal ordering algorithms. The algorithm can be employed in a variety of distributed computing environments. Its energy efficiency and low bandwidth requirement make it especially suitable for mobile computing systems. We show how to employ the algorithm for causally ordered multicasting of messages in mobile computing environments.     

Hard Real-Time Communication with the Timed Token Protocol: Current State and Challenging Problems

With the increasing use of distributed real-time systems, the ability of communication networks to handle real-time traffic is becoming more and more important. The timed token medium access control protocol, which has been now incorporated into several network standards such as FDDI and SAFENET due to its special timing property of bounded medium access time, is one of the most suitable and attractive candidate communication protocols for supporting distributed hard real-time applications. Extensive research has been conducted on using the timed token protocol to guarantee timely transmission of messages in a communication environment with hard real-time requirements. This paper intends to present a comprehensive review on recent advances in hard real-time communication with the timed token protocol. In addition, several challenging problems are identified.     

Optimal NODUP all-to-all broadcast schemes in distributed computingsystems

Broadcast, referring to a process of information dissemination in a distributed system whereby a message originating from a certain node is sent to all other nodes in the system, is a very important issue in distributed computing. All-to-all broadcast means the process by which every node broadcasts its certain piece of information to all other nodes. In this paper, we first develop the optimal all-to-all broadcast scheme for the case of one-port communication, which means that each node can only send out one message in one communication step, and then, extend our results to the case of multi-port communication, i.e., k-port communication, meaning that each node can send out k messages in one communication step. We prove that the proposed schemes are optimal for the model considered in the sense that they not only require the minimal number of communication steps, but also incur the minimal number of messages     

一种基于网络分解的多播通讯路由方法

有效的消息通讯是提高分布存储器并行计算机性能的关键因素．点对点通讯和广播通讯是２种常用的消息通讯方法，而多播通讯（Ｍｕｌｔｉｃａｓｔｉｎｇ）是指从一个源节点同时给任意多个目标节点发送消息，这种通讯比点对点和广播２种方式更具一般性，适用于很多实际应用的需求．本文针对ＰＡＲ９５并行计算机的二维网格结构，提出一种基于网络分解的多播消息通讯方法，并比较了该方法与用多个点对点方法实现多播通讯的性能.     

Repetition-based cooperative broadcasting for vehicular ad-hoc networks

In vehicular ad hoc networks, most of critical applications involved with safety rely on reliable broadcast communications with low latency. Recently, repetition-based protocols have been proposed to meet the requirements of timeliness and reliability for broadcasting. In these protocols, a sender repeatedly retransmits the broadcast message during the lifetime of the message. However, existing protocols face serious problems such as deterioration of the signal quality caused by wireless fading. In particular, since excessive repetitions might cause network congestion and waste channel resources, reliability of broadcasting should be achieved with as small a number of repetitions as possible. In this paper, we therefore propose a novel repetition-based broadcast protocol which exploits a cooperative diversity technique (called RB-CD) making a small number of repetitions robust for wireless fading. To support this cooperative diversity, neighboring nodes transmit the same message almost simultaneously (that is, using the same repetition pattern for each other) in order to form a virtual antenna array. The virtual antenna array achieves a diversity gain at the receivers. In the RB-CD protocol, the virtual antenna array consists of the source and some of its neighbors (called relays) which participate in repeating the transmission of a broadcast message. In addition, a new distributed relay selection algorithm is introduced in the RB-CD protocol. From the ns-2 simulation results, we verified that RB-CD provides a more reliable broadcasting service due to its capability of exploiting cooperative diversity.     

RMP: fault-tolerant group communication

Based on a logical token ring, this communication protocol ensures total message ordering and atomic delivery, so all group members maintain an identical view of ordered events. RMP (Reliable Multicast Protocol) is an efficient multicast protocol for general distributed applications based on the logical token ring approach. The novelty of RMP is that it simultaneously multicasts an ordered message and implicitly rotates the token position on the ring. There is no token transfer message in the normal multicast. For message atomicity, our protocol minimizes control messages and communication costs while incurring a relatively short delay. In contrast to other token algorithms, RMP does not risk losing the token when the token site fails. Without requiring extra overhead, our approach guarantees total ordering of messages and message atomicity-either every member receives a message, or none do     

Concurrent Broadcast for Information Dissemination

Concurrent broadcast involves the dissemination of a database, consisting of messages initially distributed among the nodes of a network, so that a copy of the entire database eventually resides at each node. One application is the dissemination of network status information for adaptive routing in a communications network. This paper examines the time complexity and communication complexity of several distributed procedures for concurrent broadcast. The procedures do not use information depending on the network topology. The worst-case time complexity of a flooding procedure for concurrent broadcast is shown to be linear in the number of nodes plus the number of messages, and no other procedure for concurrent broadcast has a better worst-case time complexity. A variant of flooding is proposed to eliminate redundant message receipts from the flooding process by real-time signaling between neighbors concerning messages residing at each. This variant can reduce communication complexity, while having a worst-case time complexity similar in form to that of the flooding procedure. Special properties of concurrent broadcast in a tree are also given. The present time complexity results can be used to bound the time during which inconsistent databases may reside at different nodes, to evaluate and compare procedures for (or including) concurrent broadcast, and to schedule a sequence of instances of concurrent broadcast so that the instances do not overlap and there is no need for sequence numbers.     

三方认证协议BNV的分析及改进

多个主体之间的安全会话需要有可靠的多方认证协议来保证。基于安全协议的操作语义模型,分析了三方认证协议BNV的安全性,结果表明该协议存在一致性和同步性缺陷。为此,修改了协议的消息结构并添加了标识协议主体身份的消息项。对改进后协议的安全性进行分析,结果表明改进后的协议不存在原协议的缺陷,协议参与主体满足一致性与同步性要求。最后,基于改进后协议,提出了一个n方认证协议的协议原型。