Byzantine Fault Tolerance (BFT) is crucial for ensuring the resilience of Distributed Machine Learning (DML) systems during training under adversarial conditions. Among the rising corpus of research on BFT in DML, there is no comprehensive classification of techniques or broad analysis of different approaches. This paper provides an in-depth survey of recent advancements in BFT for DML, with a focus on first-order optimisation methods, particularly, the popular one Stochastic Gradient Descent (SGD) during the training phase. We offer a novel classification of BFT approaches based on characteristics such as the communication process, optimisation method, and topology setting. This classification aims to enhance the understanding of various BFT methods and guide future research in addressing open challenges in the field. This work provides the foundations for developing robust BFT systems, using a variety of optimisation methods to strengthen resilience.

In this paper, we study how users can act as witnesses to limit the spread of fake news. We present a new technique based on consulting a set of users, called witnesses. Before resharing a content$M$by a user$A$, a set of$k$users (witnesses) are selected randomly, by the system, from the friends set of$A$. Witnesses are asked to validate the content$M$after allowing the user$A$to re-share it. If there is an authenticated user$AU$, among this set of witnesses that validating$M$, the user$A$is allowed to re-share it without considering the others$(k-1)$responses. In the case where all witnesses are non-authenticated, if at least one witness rejects the content$M$, the user$A$is not allowed to re-share it. Note that$A$has no knowledge about the set of selected witnesses.

This paper tackles the problem of locating the diffusion source in networks. Designating all nodes of the network as observers for locating the diffusion source is very complex and impracticable. To make this problem solvable in a simple manner, only a subset of nodes is used as observers. Choosing these observers can be a challenging task, as the effectiveness of the observers depends on various factors including the network topology, the diffusion process, and the available resources for observing the diffusion source. Several techniques have been proposed for selecting observers citing betweenness centrality, closeness centrality, high degree nodes, and randomization. This paper advances the state of the art by proposing the first solution, to our knowledge, for locating the diffusion source problem where the observers are selected as critical nodes.

The consensus is a central problem of fault-tolerant distributed computing. Unfortunately, solving such a problem is impossible in asynchronous distributed systems prone to process failures. To circumvent this impossibility (known as FLP impossibility result) in a deterministic way, on top of asynchronous distributed systems enriched with additional assumptions, several protocols have been proposed. Actually, to solve the Byzantine Consensus problem, with a deterministic manner, in systems where at most t processes may exhibit a Byzantine behavior, two approaches have been investigated. The first relies on the addition of synchrony, called Timer-Based, while the second, called Time-Free, is based on the pattern of message exchange. This paper shows that both types of assumptions are not antagonist and can be combined to solve authenticated Byzantine consensus. The combined assumption considers a correct process p i , called ⋄〈 t + 1〉-BW, and a set X of t+1 correct processes (including p i itself) such that, eventually, for each query broadcasted by a correct process p j of X, p j receives a response from p i ∈ X among the ( n – t) first responses to that query or both links connecting p i and p j are timely. Based on this combination, a simple hybrid authenticated Byzantine consensus protocol benefiting from the best of both worlds is proposed. As a matter of fact, although numerous hybrid protocols have been designed for the consensus problem in the crash model, this is, to our knowledge, the first hybrid deterministic solution to the Byzantine consensus problem.

A wireless sensor network (WSN) is a set of sensor nodes devoted to sense sizes of physical phenomena of a geographical area of interest. The sensed data so collected are transmitted to a specific node called sink via cluster-heads (CHs). In most wsn's applications, CHs play an important role in aggregation and transmission of sensed data. Indeed, a failed CH may abort the overall mission of the sub-network. Due to their crucial functions, CHs must be designed and maintained to be robust enough in order to face trouble coming from the harsh environment. Therefore, each failed CH should be detected, recovered and a new one takes the relay without data loss. In this paper, we propose a novel algorithm called Cluster-Head Recovery Algorithm (CHRA). In this algorithm, a checkpointing technique is used to save CH's state in order to create a recovery path within each cluster. We compute the node's failure probability through a Bayesian network. The efficiency of the proposal is that can detect and recover the CH's failure online and in a distributed manner. The proposed scheme functionalities have been conducted by simulation and the obtained results demonstrate the effectiveness of the proposal.

This article is on broadcast and agreement in asynchronous message-passing systems made up of n processes, and where up to t processes may have a Byzantine Behavior. Its first contribution is a powerful, yet simple, all-to-all broadcast communication abstraction suited to binary values. This abstraction, which copes with up to t < n /3 Byzantine processes, allows each process to broadcast a binary value, and obtain a set of values such that (1) no value broadcast only by Byzantine processes can belong to the set of a correct process, and (2) if the set obtained by a correct process contains a single value v , then the set obtained by any correct process contains v . The second contribution of this article is a new round-based asynchronous consensus algorithm that copes with up to t < n /3 Byzantine processes. This algorithm is based on the previous binary broadcast abstraction and a weak common coin. In addition to being signature-free and optimal with respect to the value of t , this consensus algorithm has several noteworthy properties: the expected number of rounds to decide is constant; each round is composed of a constant number of communication steps and involves O ( n 2) messages; each message is composed of a round number plus a constant number of bits. Moreover, the algorithm tolerates message reordering by the adversary (i.e., the Byzantine processes).

This paper presents a new round-based asynchronous consensus algorithm that copes with up to t

This paper presents a simple protocol that solves the authenticated Byzantine Consensus problem in asynchronous distributed systems. To circumvent the FLP impossibility result in a deterministic way, synchrony assumptions should be added. In the context of Byzantine failures for systems where at most t processes may exhibit a Byzantine behavior and where not all the system is assumed eventually synchronous, Moumen et al. provide the main result. They assume at least one correct process, called 2t-bisource, connected with 2t privileged neighbors with eventually timely outgoing and incoming links. The present paper shows that a deterministic solution for the authenticated byzantine consensus problem is possible if the system model satisfies an additional assumption that does not rely on physical time but on the pattern of messages that are exchanged. The basic message exchange between processes is the query-response mechanism. To solve the Consensus problem, we assume a correct process p, called 2t-winning process, and a set Q of 2t processes such that, eventually, for each query issued by p, any process q of Q receives a response from p among the (n - t) first responses to that query. The processes in the set Q can exhibit a Byzantine behavior and this set may change over time. Whereas many time-free solutions have been designed for the consensus problem in the crash model, this is, to our knowledge, the first time-free deterministic solution to the Byzantine consensus problem.