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Model-based attack tolerance
No full textInternational audienceSoftware-based systems are nowadays complex and highly distributed. In contrast, existing intrusion detection mechanisms are not always suitable for protecting these systems against new and sophisticated attacks that increasingly appear. In this paper, we present a new generic approach that combines monitoring and formal methods in order to ensure attack-tolerance at a high level of abstraction. Our experiments on an authentication Web application show that this method is effective and realistic to tolerate a variety of attack
Monotonic Basin Hopping for the separation of acid gases from crude natural gas
No full textMembrane gas separation processes are considered as one of the most attractive separation technologies for the development of sustainable industries. The process architecture can be complex and the identification of the optimal design addresses a formidable computational challenge. The main objective of this paper is to study the effectiveness of MBH algorithm to find efficient configurations for the problem of the separation of acid gases from crude natural gas. The comparison with a state of the art paper is used to valide our method
Study of a combinatorial game in graphs through Linear Programming
No full textInternational audienceIn the Spy Game played on a graph G, a single spy travels the vertices of G at speed s, while multiple slow guards strive to have, at all times, one of them within distance d of that spy. In order to determine the smallest number of guards necessary for this task, we analyze the game through a Linear Programming formulation and the fractional strategies it yields for the guards. We then show the equivalence of fractional and integral strategies in trees. This allows us to design a polynomial-time algorithm for computing an optimal strategy in this class of graphs. Using duality in Linear Programming, we also provide non-trivial bounds on the fractional guard-number of grids and torus. We believe that the approach using fractional relaxation and Linear Programming is promising to obtain new results in the field of combinatorial games
A Glimpse into the World of Integrative and Mobilizable Elements in Streptococci Reveals an Unexpected Diversity and Novel Families of Mobilization Proteins
No full textInternational audienceRecent analyses of bacterial genomes have shown that integrated elements that transfer by conjugation play an essential role in horizontal gene transfer. Among these elements, the integrative and mobilizable elements (IMEs) are known to encode their own excision and integration machinery, and to carry all the sequences or genes necessary to hijack the mating pore of a conjugative element for their own transfer. However, knowledge of their prevalence and diversity is still severely lacking. In this work, an extensive analysis of 124 genomes from 27 species of Streptococcus reveals 144 IMEs. These IMEs encode either tyrosine or serine integrases. The identification of IME boundaries shows that 141 are specifically integrated in 17 target sites. The IME-encoded relaxases belong to nine superfamilies, among which four are previously unknown in any mobilizable or conjugative element. A total of 118 IMEs are found to encode a non-canonical relaxase related to rolling circle replication initiators (belonging to the four novel families or to MobT). Surprisingly, among these, 83 encode a TcpA protein (i.e., a non-canonical coupling protein (CP) that is more closely related to FtsK than VirD4) that was not previously known to be encoded by mobilizable elements. Phylogenetic analyses reveal not only many integration/excision module replacements but also losses, acquisitions or replacements of TcpA genes between IMEs. This glimpse into the still poorly known world of IMEs reveals that mobilizable elements have a very high prevalence. Their diversity is even greater than expected, with most encoding a CP and/or a non-canonical relaxase
A scalable and systolic architectures of montgomery modular multiplication for public key cryptosystems based on dsps
No full textInternational audienc
Contribution à la modélisation des performances des systèmes de communications sans fil embarqués dans les véhicules automobiles
No full textThe general framework of this Ph.D. thesis deals with Vehicle to Vehicle (V2V) communications. This communication is principally dedicated to reinforce security through exchange of information between vehicles in case of unexpected events. The development of V2V solutions requires the understanding and merging of a number of techniques from several communication technology areas. Indeed, the performance of these systems are related to three main blocks: the implementation of the modems, the antenna configuration and the fast varying electromagnetic environment surrounding the transmitter and the receiver. The purpose of this PhD thesis is precisely to elaborate a design strategy to investigate all the different blocks constituting the communication chain. The ultimate goal is to optimize antenna selection and location on board the vehicle. In the first place, we proposed a geometry-based stochastic channel modelling approach to develop virtual dynamic scenarios. It was shown that the most common propagation environments such as rural, highway or urban-like propagation channels are reached through adjustment or numbers and location of simple metallic plates. Using this method, we are able to emulate the characteristics, such as the delay spread, angles of arrival distribution and the Doppler spectrum, of these typical driving scenarios. Moreover, we dealt with antenna integration problems in the second part of this work. A study on the simplification of numerical models of vehicles was carried out. Furthermore in this section, we investigated the limit of validity of representing the integrated antenna on board vehicle solely by its radiation pattern. We deduced from this study that the interactions with the elements present in the near-field is no longer valid. Thus, a strategy to alleviate the degree of error was found upon consideration of the near-field scatter in the a-priori simulation of the antenna integrated on the vehicle. In the third part of this thesis, we evaluated the performance of different antenna configurations in terms of packet error rate after the embodiment of the PHY layer of the LEEE 802.11p standard. Simulation results, for each antenna configurations, was given for several combinations of PHY layer parameters such as data rate and packet length. The last part of this manuscript is dedicated to the presentation of a measurement campaign that was carried out in a rural driving environment. Results obtained from these functional tests were confronted with simulation results to demonstrate the strength of the latter. We found that the expected trends in communication performance in terms of PER are globally predictable from our model though we obtained surprising results in some cases, needing further investigation.Le cadre général de cette thèse porte sur les communications véhicule à véhicule (V2V). L'objectif principal de ce type de communication est d'améliorer la sécurité routière et d'optimiser la fluidité du trafic. Les performances de systèmes de communication embarqués dépendent principalement de la configuration des antennes, du type de récepteurs utilisés (modem) et du canal de propagation. Le sujet de la thèse se concentre précisément sur l'élaboration d'un outil de simulation robuste et fiable pour optimiser les choix technologiques d'antennes et leurs implantations à bord. Il permettra de limiter ainsi le recours aux prototypes et aux essais de roulage. Dans un premier temps, nous avons proposé une méthode de type géométrique-stochastique pour modéliser des canaux de propagation d'un système de communication V2V. Cette méthode permet de définir des scénarios dynamiques et sa flexibilité nous offre l'opportunité de paramétrer les caractéristiques d'un canal de propagation. Nous montrons pour l'essentiel de quelle manière l'agencement et le nombre de diffuseurs de forme simple peuvent contribuer à influencer les statistiques de l'étalement des retards, la distribution des angles d'arrivée et les spectres Doppler. Dans la deuxième partie de ces travaux, nous nous focalisons sur la problématique d'intégration d'antenne. Il a été constaté qu'il est particulièrement utile de simplifier la maquette numérique du véhicule complet lors d'une simulation électromagnétique de l'antenne intégrée à bord de ce véhicule. De plus, dans cette section, nous avons étudié la limite de la validité de substitution d'une antenne intégrée à bord par son seul diagramme de rayonnement dans les modèles de canaux de propagation. A partir de cette étude, nous en avons déduit, que les interactions électromagnétiques avec les éléments se situant dans le champ-proche n'étaient plus valides. Ainsi, une stratégie de correction a été trouvée en considérant l'élément en champ proche dans la simulation initiale de l'antenne intégrée sur le véhicule. L'évaluation des performances d'antennes, en termes de taux d'erreurs paquet, après l'implémentation de la couche physique du standard 802. 11 p, est au cœur de la troisième partie de cette thèse. Des résultats de simulation, pour chaque configuration d'antenne, ont été donnés pour plusieurs combinaisons de paramètres de couche PHY tels que le débit et la longueur de paquet. La dernière partie de ce manuscrit traite de la présentation d'une campagne de mesure qui a été réalisée principalement dans un environnement de type rural. Les essais de roulage avaient pour but de démontrer la capacité des méthodes de simulation à faire un choix approprié d'installation d'antenne. Nous avons constaté que les tendances attendues des performances de communication en termes de PER sont globalement prévisibles à partir de notre modèle bien que nous ayons obtenu des résultats surprenants dans certains cas. Ce qui nécessitera une enquête plus approfondie
Computational Homogenization of the Nonlinear Electrical Behavior of Graphene/Polymer Nanocomposites
No full textInternational audienc
Distributed faulty node detection in DTNs in presence of Byzantine attack
No full textInternational audienceThis paper considers a delay tolerant network consisting of nodes equipped with sensors, some of them producing outliers. A distributed faulty node detection (DFD) algorithm, whose aim is to help each node in estimating the status of its sensors, has been proposed recently by the authors. The aim of this paper is to analyze the robustness of the DFD algorithm to the presence of misbehaving nodes performing Byzantine attacks. Two types of attacks are considered and analyzed, each trying to mislead the other nodes in the estimation of the status of their sensors. This provides insights on the way the parameters of the DFD algorithm should be adapted to minimize the impact of misbehaving nodes. Theoretical results are illustrated with simulations considering nodes with random displacements, as well as traces of node inter-contact times from real databases
Infotaxie collective : coordonner une équipe d'agents pour trouver une source
No full textRapport de stage de Licence 3National audienceCe stage a pour objectif de concevoir et d’étudier un système dynamique discret,construit à partir d’automates cellulaires et de systèmes multi-agents, qui répond au problèmede l’infotaxie. Le problème de l’infotaxie consiste pour des individus sans mémoire et avec unperception limitée de leur environnement à retrouver une source qui émet un signal. Ce signala la particularité que les agents ne peuvent ni mesurer son intensité, ni déterminer la directionde laquelle il vient lorsqu’ils le détectent. Ce modèle s’inspire du comportement d’unecertaine espèce d’amibes sociales et de leur stratégie de regroupement