Malicious Faults Research Articles

Efficient multicasting agreement protocol

The fault-tolerance is an important research topic in the study of distributed systems. To cope with the influence from faulty components, reaching a common agreement at the presence of faults before performing some special tasks is essential. Therefore, the Byzantine agreement (BA) problem has drawn more and more of the researchers' attention as they explore deeper and deeper into the world of distributed systems. Traditionally, the BA problem has been visited in a Fully Connected Network (FCN), BroadCasting Network (BCN) or Generalize Connected Network (GCN), making the malicious fault assumption with processors or communication media grows into the dual failure mode on both processors and communication media. However, the network structures (topologies) of FCN, BCN and GCN are not practical nowadays. In this study, we shall take a close look at the limits of the network structure to revisit the BA problem with a Multi-Casting Network (MCN). FCN, BCN and GCN are all special cases of MCN, so the new protocol we shall propose here will also be able to solve the BA problem with FCN, BCN and GCN structures. Our new protocol uses a minimum number of rounds of message exchange and can tolerate a maximum number of allowable faulty components and make each fault-free processor reach a common agreement in an MCN.

Secure distributed storage and retrieval

In his well-known Information Dispersal Algorithm paper, Rabin showed a way to distribute information in n pieces among n servers in such a way that recovery of the information is possible in the presence of up to t inactive servers. An enhanced mechanism to enable construction in the presence of malicious faults, which can intentionally modify their pieces of the information, was later presented by Krawczyk. Yet, these methods assume that the malicious faults occur only at reconstruction time. In this paper we address the more general problem of secure storage and retrieval of information (SSRI), and guarantee that also the process of storing the information is correct even when some of the servers fail. Our protocols achieve this while maintaining the (asymptotical) space optimality of the above methods. We also consider SSRI with the added requirement of confidentiality, by which no party except for the rightful owner of the information is able to learn anything about it. This is achieved through novel applications of cryptographic techniques, such as the distributed generation of receipts, distributed key management via threshold cryptography, and “blinding”. An interesting byproduct of our scheme is the construction of a secret sharing scheme with shorter shares size in the amortized sense. An immediate practical application of our work is a system for the secure deposit of sensitive data. We also extend SSRI to a “proactive” setting, where an adversary may corrupt all the servers during the lifetime of the system, but only a fraction during any given time interval.

Exploiting omissive faults in synchronous approximate agreement

In a fault-tolerant distributed system, it is often necessary for nonfaulty processes to agree on the value of a shared data item. The criterion of Approximate Agreement does not require processes to achieve exact agreement on a value; rather, they need only agree to within a predefined numerical tolerance. Approximate Agreement can be achieved through convergent voting algorithms. Previous research has studied convergent voting algorithms under mixed-mode or hybrid fault models, such as the Thambidurai and Park Hybrid fault model, comprised of three fault modes: asymmetric, symmetric, and benign. This paper makes three major contributions to the state of the art in fault-tolerant convergent voting. (1) We partition both the asymmetric and symmetric fault modes into disjoint omissive and transmissive submodes. The resulting five-mode hybrid fault model is a superset of previous hybrid fault models. (2) We present a new family of voting algorithms, called Omission Mean Subsequence Reduced (OMSR), which implicitly recognize and exploit omissive behavior in malicious faults while still maintaining full Byzantine fault tolerance; (3) We show that OMSR voting algorithms are more fault-tolerant than previous voting algorithms if any of the currently active faults is omissive.

A separable method for incorporating imperfect fault-coverage into combinatorial models

This paper presents a new method for incorporating imperfect FC (fault coverage) into a combinatorial model. Imperfect FC, the probability that a single malicious fault can thwart automatic recovery mechanisms, is important to accurate reliability assessment of fault-tolerant computer systems. Until recently, it was thought that the consideration of this probability necessitated a Markov model rather than the simpler (and usually faster) combinatorial model. SEA, the new approach, separates the modeling of FC failures into two terms that are multiplied to compute the system reliability. The first term, a simple product, represents the probability that no uncovered fault occurs. The second term comes from a combinatorial model which includes the covered faults that can lead to system failure. This second term can be computed from any common approach (e.g. fault tree, block diagram, digraph) which ignores the FC concept by slightly altering the component-failure probabilities. The result of this work is that reliability engineers can use their favorite software package (which ignores the FC concept) for computing reliability, and then adjust the input and output of that program slightly to produce a result which includes FC. This method applies to any system for which: the FC probabilities are constant and state-independent; the hazard rates are state-independent; and an FC failure leads to immediate system failure.

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimal agreement protocol in malicious faulty processors and faulty 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. >

A note on the complexity of reliability in neural networks

It is shown that in a standard discrete neural network model with small fan-in, tolerance to random malicious faults can be achieved with a log-linear increase in the number of neurons and a constant factor increase in parallel time, provided fan-in can increase arbitrarily. A similar result is obtained for a nonstandard but closely related model with no restriction on fan-in.

An improved hardware implementation of the fault-tolerant clock synchronization algorithm for large multiprocessor systems

An improved implementation of clock synchronization of multiprocessor systems in the presence of malicious faults is proposed. The proposed hardware implementation for the reference clock selection has a lower gate complexity, smaller time delay, and greater flexibility than the previously published implementation. The improvement is achieved by replacing the sorter with a counting encoder and comparators and by introducing threshold generation logic with programmable registers. The scheme has a gate complexity of O(n) and a delay of O(log n), where n is the total number of inputs to a particular clock, and is programmable for different values of n and m, the maximum number of faults.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Distributed Graph Recognition with Malicious Faultsa

Distributed Graph Recognition with Malicious Faults^a

Transmission delays in hardware clock synchronization

Various methods, both with software and hardware, have been proposed to synchronize a set of physical clocks in the system. Software methods are very flexible and economical but suffer an excessive time overhead, whereas hardware methods require no time overhead but are unable to handle transmission delays in clock signals. The effects of nonzero transmission delays in synchronization have been studied extensively in the communication area in the absence of malicious or Byzantine faults. The authors show that it is easy to incorporate the ideas from the communication area into the existing hardware clock synchronization algorithms in order to take into account the presence of both malicious faults and nonzero transmission delays.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Clock Synchronization of a Large Multiprocessor System in the Presence of Malicious Faults

Clock synchronization in the presence of malicious faults is one of the main problems associated with the design of a multiprocessor system. Although over the past few years many different algorithms have been proposed for overcoming this problem, they are not suitable for a large real-time multiprocessor system due to their excessive time overhead, asymmetric structure, and/or large number of interconnections. To remedy this problem, we propose a new method in this paper that i) requires little time overhead by using phase-locked clock synchronization, ii) needs a clock network very similar to the processor network, and iii) uses only 20-30 percent of the total number of interconnections required by a fully connected network for almost no loss in the synchronizing capabilities. Both ii) and iii) are made possible by grouping the various clocks in the system into many different clusters and then treating the clusters themselves as single clock units as far as the network is concerned. The method is significant in that regardless of their size multiprocessor systems can be built at an inexpensive cost without sacrificing both the synchronization and fault tolerance capabilities. To show the feasibility of our method, an example hardware implementation is presented. This implementation turns out to be much simpler than the other existing methods and also retains the symmetry and synchronizing capabilities of the network.