byzantine agreement

Abstract—The popularity of wide-area computer services has generated a compelling need for efficient algorithms that provide high reliability. Byzantine fault-tolerant (BFT) algorithms can be used with this purpose because they allow replicated systems to continue to provide a correct service even when some of their replicas fail arbitrarily, either accidentally or due to malicious faults. Current BFT algorithms perform well on LANs but when the replicas are distributed geographically their performance is affected by the lower bandwidth and the ...

In this paper we consider a model where malicious agents can corrupt hosts and move around in a network of processors. We consider a family of mobilefault models MF( t n-1 , ρ). In MF( t n-1 , ρ) there are a total of n processors, the maximum number of mobile faults is t, and their roaming pace is ρ (for example, ρ = 3 means that it takes an agent at least 3 rounds to "hop" to the next host). We study in these models the classical testbed problem for fault-tolerant distributed computing: Byzantine agreement. It has been shown that if ρ = 1, then agreement cannot be reached in the presence of even one fault, unless one of the processors remains uncorrupted for a certain amount of time. Subject to this proviso, we present a protocol for MF( 1 3 , 1), which is optimal. The running time of the protocol is O(n) rounds, also optimal for these models.

In a heterogeneous ubiquitous peer-to-peer network, different peers may provide different qualities of service, and hence it is very important and helpful to identify those peers that can provide better services than others. In this paper, we use a reputation value to represent the quality of service offered by a peer. We design a novel reputation model which enables any peer to calculate the reputation value of any other peer, so as to differentiate peers that provide good quality of service from peers that provide poor or even faulty service. In order to speed up the convergence of reputation calculation, a peer collects recommendations from its neighbor peers. On the other hand, in order to overcome the problem of malicious recommendations, we propose an auxiliary trust mechanism which calculates a trust value for each peer. Our experimental results show that the reputation model achieves a fast convergence speed, and it is robust against a large portion of malicious peers that provide fraud recommendations.

Abstract. This paper considers a variant of the Byzantine Generals problem, in which processes start with arbitrary real values rather than Boolean values or values from some bounded range, and in which approximate, rather than exact, agreement is the desired goal. Algorithms are presented to reach approximate agreement in asynchronous, as well as synchronous systems. The asynchronous agreement algorithm is an interesting contrast to a result of Fischer et al, who show that exact agreement with guaranteed termination is not attainable in an asynchronous system with as few as one faulty process. The algorithms work by successive approximation, with a provable convergence rate that depends on the ratio between the number of faulty processes and the total number of processes. Lower bounds on the convergence rate for algorithms of this form are proved, and the algorithms presented are shown to

The Web Service Atomic Transactions (WS-AT) specification makes it possible for businesses to engage in standard distributed transaction processing over the Internet using Web Services technology. For such business applications, trustworthy coordination of WS-AT is crucial. In this paper, we explain how to render WS-AT coordination trustworthy by applying Byzantine fault tolerance (BFT) techniques. More specifically, we show how to protect the core services described in the WS-AT specification, namely, the Activation service, the Registration service, the Completion service and the Coordinator service, against Byzantine faults. The main contribution of this work is that it exploits the semantics of the WS-AT services to minimize the use of Byzantine agreement, instead of applying BFT techniques naively, which would be prohibitively expensive. We have incorporated our BFT protocols and mechanisms into an open-source framework that implements the WS-AT specification. The resulting BFT framework for WS-AT is useful for business applications that are based on WS-AT and that require a high degree of dependability, security and trust.

The Scalable Processor-Independent Design for Electromagnetic Resilience (SPIDER) is a new family of fault-tolerant architectures under development at NASA Langley Research Center (LaRC). The SPIDER is a general-purpose computational platform ...

Quantum mechanics is the current best description of the world as we know it. Experiments have shown that quantum predictions are accurate up ten places of decimal. In quantum cryptography much work has been devoted to the study of Quantum Key Distribution (QKD). The purpose of QKD is to securely distribute secret keys between the users in a network. As a result, several quantum cryptographic protocols have been implemented and tested after the advent of quantum computing. In this paper, we have given a brief overview of QKD, and some practical networks that integrate QKD in the current Internet security architecture. We have also discussed some aspects of quantum network security with particular attention to Byzantine Agreement Protocol.