La stéganographie numérique est une technique récente qui a émergé comme une source importante pour la sécurité des données. Elle consiste à envoyer secrètement et de manière fiable des informations dissimulées et non pas seulement à masquer leur présence. Elle exploite les caractéristiques des fichiers médias numériques anodins, tels que l’image, le son et la vidéo,et les utilise comme support pour véhiculer des informations secrète d’une façon inaperçue. Les techniques de cryptage et de tatouage sont déjà utilisées pour résoudre les problèmes liés à la sécurité des données. Toutefois,l’évolution des tentatives d’interception et de déchiffrement des données numériques nécessitent de nouvelles techniques pour enrayer les tentatives malveillantes et d’élargir le champ des applications y associées. L’objectif principal des systèmes stéganographiques consiste à fournir de nouveaux moyens sécurisés, indétectables et imperceptibles pour dissimuler des données.La stéganographie est utilisée sous l’hypothèse qu’elle ne sera pas détectée si personne n’essaye de la découvrir. Les techniques récentes destéganographie ont déjà été employées dans diverses applications. La majorité de ces applications ont pour objectif d’assurer la confidentialité des données.D’autres par contre sont utilisées malicieusement. L’utilisation de la stéganographie à des fins criminelles, de terrorisme, d’espionnage ou de piraterie constitue une menace réelle. Ces tentatives malveillantes de communiquer secrètement ont récemment conduit les chercheurs à inclure une nouvelle branche de recherche: la stéganalyse, pour contrer les techniques stéganographique. L’objectif principal de la stéganalyse est de détecter la résence potentielle d’un message dissimulé dans un support numérique et ne considère pas nécessairement son extraction. La parole numérique constitue un terrain de prédilection pour dissimuler des données numériques. En effet, elle est présente en abondance grâce aux technologies de télécommunications fixes ou mobiles et aussi à travers divers moyens de stockage de l’audio numérique. Cette thèse étudie la stéganographie et la stéganalyse utilisant la voix numérisée comme support et vise à (1) présenter un algorithme qui répond aux exigences des systèmes stéganographiques reliées à la capacité élevée, l’indétectabilité et l’imperceptibilité des données dissimulées, (2) le contrôle de la distorsion induite par le processus de dissimulation des données (3) définir un nouveau concept de zones spectrales dans le domaine de Fourier utilisant et l’amplitude et la phase (4) introduire un nouveau algorithme de stéganalyse basé sur les techniques de compression sans pertes d’information à la fois simple et efficace. La performance de l’algorithme stéganographique est mesurée par des méthodes d’évaluation perceptuelles et statistiques. D’autre part, la performance de l’algorithme de stéganalyse est mesurée par la capacité du système à distinguer entre un signal audio pur et un signal audio stéganographié. Les résultats sont très prometteurs et montrent des compromis de performance intéressants par rapport aux méthodes connexes. Les travaux futurs incluent essentiellement le renforcement de l’algorithme de stéganalyse pour qu’il soit en mesure de détecter une faible quantité de données dissimulées. Nous planifions également l’intégration de notre algorithme de stéganographie dans certaines plateformes émergentes telles que l’iPhone. D’autres perspectives consistent à améliorer l’algorithme stéganographique pour que les données dissimulées soit résistantes au codage de la parole, au bruit et à la distorsion induits parles canaux de transmission. / Digital steganography is a young flourishing science emerged as a prominent source of data security. The primary goal of steganography is to reliably send hidden information secretly, not merely to obscure its presence. It exploits the characteristics of digital media files such as: image, audio, video, text by utilizing them as carriers to secretly communicate data. Encryption and watermarking techniques are already used to address concerns related to datasecurity. However, constantly-changing attacks on the integrity of digital data require new techniques to break the cycle of malicious attempts and expand the scope of involved applications. The main objective of steganographic systems is to provide secure, undetectable and imperceptible ways to conceal high-rate of data into digital medium. Steganography is used under the assumption that it will not be detected if no one is attempting to uncover it. Steganography techniques have found their way into various and versatile applications. Some of these applications are used for the benefit of people others are used maliciously. The threat posed by criminals, hackers, terrorists and spies using steganography is indeed real. To defeat malicious attempts when communicating secretly, researchers’ work has been lately extended toinclude a new and parallel research branch to countermeasure steganagraphy techniques called steganalysis. The main purpose of steganalysis technique is to detect the presence or not of hidden message and does not consider necessarily its successful extraction. Digital speech, in particular, constitutes a prominent source of data-hiding across novel telecommunication technologies such as covered voice-over-IP, audio conferencing, etc. This thesis investigatesdigital speech steganography and steganalysis and aims at: (1) presenting an algorithm that meets high data capacity, undetectability and imperceptibility requirements of steganographic systems, (2) controlling the distortion induced by the embedding process (3) presenting new concepts of spectral embedding areas in the Fourier domain which is applicable to magnitude and phase spectrums and (4) introducing a simple yet effective speech steganalysis algorithm based on lossless data compression techniques. The steganographic algorithm’s performance is measured by perceptual and statistical evaluation methods. On the other hand, the steganalysis algorithm’s performance is measured by how well the system can distinguish between stego- and cover-audio signals. The results are very promising and show interesting performance tradeoffs compared to related methods. Future work is based mainly on strengthening the proposed steganalysis algorithm to be able to detect small hiding capacity. As for our steganographic algorithm, we aim at integrating our steganographic in some emerging devices such as iPhone and further enhancing the capabilities of our steganographic algorithm to ensure hidden-data integrity under severe compression, noise and channel distortion.

Recent developments in the field of parallel and distributed computing has led to a proliferation of solving large and computationally intensive mathematical, science, or engineering problems, that consist of several parallelizable parts and several non-parallelizable (sequential) parts. In a parallel and distributed computing environment, the performance goal is to optimize the execution of parallelizable parts of an application on concurrent processors. This requires efficient application scheduling and resource allocation for mapping applications to a set of suitable parallel processors such that the overall performance goal is achieved. However, such computational environments are often prone to unpredictable variations in application (problem and algorithm) and system characteristics. Therefore, a robustness study is required to guarantee a desired level of performance. Given an initial workload, a mapping of applications to resources is considered to be robust if that mapping optimizes execution performance and guarantees a desired level of performance in the presence of unpredictable perturbations at runtime. In this research, a stochastic process algebra, Performance Evaluation Process Algebra (PEPA), is used for obtaining resource allocations via a numerical analysis of performance modeling of the parallel execution of applications on parallel computing resources. The PEPA performance model is translated into an underlying mathematical Markov chain model for obtaining performance measures. Further, a robustness analysis of the allocation techniques is performed for finding a robustmapping from a set of initial mapping schemes. The numerical analysis of the performance models have confirmed similarity with the simulation results of earlier research available in existing literature. When compared to direct experiments and simulations, numerical models and the corresponding analyses are easier to reproduce, do not incur any setup or installation costs, do not impose any prerequisites for learning a simulation framework, and are not limited by the complexity of the underlying infrastructure or simulation libraries.

<div>As wearable devices, like smartwatches and fitness monitors, gain popularity and are being touted for clinical purposes, evaluating the resilience and security of wearable operating systems (OSes) and their corresponding ecosystems becomes essential. One of the most dominant OSes for wearable devices is Wear OS, created by Google. Wear OS and Android (its counterpart OS for mobile devices) share similar features, but the unique characteristics and uses of wearable devices posses new challenges. For example, wearable applications are generally more dependent on device sensors, have complex communication patterns (both intra-device and inter-device), and are context-aware. Current research efforts on the Wear OS are more focused on the efficiency and performance of the OS itself, overlooking the resilience or security of the OS or its ecosystem.</div><div> </div><div>This dissertation introduces a systematic analysis to evaluate the Wear OS's resilience and security. The work is divided into two main parts. First, we focus our efforts on developing novel tools to evaluate the robustness of the wearable OS and uncover vulnerabilities and failures in the wearable ecosystem. We provide an assessment and propose techniques to improve the system's overall reliability. Second, we turn our attention to the security and privacy of smart devices. We assess the privacy and security of highly interconnected devices. We demonstrate the feasibility of privacy attacks under these scenarios and propose a defense mechanism to mitigate these attacks.</div><div> </div><div>For the resilience part, we evaluate the overall robustness of the Wear OS ecosystem using a fuzz testing-based tool [DSN2018]. We perform an extensive fault injection study by mutating inter-process communication messages and UI events on a set of popular wearable and mobile applications. The results of our study show similarities in the root cause of failures between Wear OS and Android; however, the distribution of exception differ in both OSes. Further, our study evidence that input validation has improved in the Android ecosystem with respect to prior studies. Then, we study the impact of the state of a wearable device on the overall reliability of the applications running in Wear OS [MobiSys2020]. We use distinguishable characteristics of wearable apps, such as sensor activation and mobile-wearable communication patterns, to derive a state model and use this model to target specific fuzz injection campaigns against a set of popular wearable apps. Our experiments revealed an abundance of improper exception handling on wearable applications and error propagation across mobile and wearable devices. Furthermore, our results unveiled a flawed design of the wearable OS, which caused the device to reboot due to excessive sensor use.</div><div><br></div><div>For the security and privacy part, we assess user awareness toward privacy risks under scenarios with multiple interconnected devices. Our results show that a significant majority of the users have no reservation while granting permission to their devices. Furthermore, users tend to be more conservative while granting permission on their wearables. Based on the results of our study, we demonstrate the practicability of leaking sensitive information inferred from the user by orchestrating an attack using multiple devices. Finally, we introduce a tool based on NLP (Natural Language Processing) techniques that can aid the user in detecting this type of attack.</div>

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Le comportement dynamique de structures complexes, comme les alternateurs, doit être maîtrisé afin d’en garantir un fonctionnement fiable. Cependant, la modélisation comporte de nombreuses incertitudes rendant délicates la prédiction du comportement vibratoire. Ces travaux de recherche ont pour objectif de fournir des outils d’aide à la décision afin de faciliter la prise de décision rapide suite au redémarrage d’alternateurs. Basé sur la théorie info-gap, un premier outil d’aide à la décision est proposé : il a pour objectif d’évaluer la robustesse de réponses dynamiques vis-à-vis d’un modèle modal incertain. Nous avons également étudié comment de l’information nouvelle peut être intégrée au modèle d’incertitude pour améliorer sa représentativité à la réalité.Une expansion par l’erreur en relation de comportement étendue de modes propres identifiés permet ensuite d’enrichir la représentativité du modèle numérique fournissant ainsi un modèle qualifié d’hybride et permettant d’évaluer les niveaux de réponse. Comme la modélisation comporte de nombreuses méconnaissances, nous avons proposé le procédé d’expansion robuste dont l’objectif est d’obtenir des vecteurs étendus robustes. En présence de méconnaissances sévères, nous montrons enfin qu’il est préférable de calibrer un modèle en maximisant la robustesse vis-à-vis des incertitudes plutôt qu’en maximisant uniquement la fidélité vis-à-vis des données. Couplée à des techniques de réduction de modèle et de construction de méta modèles,nous appliquons cette démarche à une structure de complexité industrielle représentative du contexte industriel. / The complex structural dynamic behavior of alternator must be well understood in order to insuretheir reliable and safe operation. The numerical model is however difficult to construct mainlydue to the presence of a high level of uncertainty. The objective of this work is to providedecision support tools in order to assess the vibratory levels in operation before to restart thealternator. Based on info-gap theory, a first decision support tool is proposed: the objective hereis to assess the robustness of the dynamical response to the uncertain modal model. Based on realdata, the calibration of an info-gap model of uncertainty is also proposed in order to enhance itsfidelity to reality. Then, the extended constitutive relation error is used to expand identified modeshapes which are used to assess the vibratory levels. The robust expansion process is proposed inorder to obtain robust expanded mode shapes to parametric uncertainties. In presence of lack-ofknowledge,the trade-off between fidelity-to-data and robustness-to-uncertainties which expressesthat robustness improves as fidelity deteriorates is emphasized on an industrial structure by usingboth reduced order model and surrogate model techniques.

Flexible structures are increasingly used in various applications such as aerospace, automotive and so on. Since they are lightly damped and susceptible to vibrations, active vibration control is desirable. In practice, in addition to achieving effective vibration reduction, we have also to consider the required control energy to avoid the energy insufficiency, the control input to avoid control saturation and reduce the effects of measurement noises. On the other hand, as flexible structures have infinite number of resonant modes and only the first few can be employed in the system modeling and the controller design, there always exist neglected high-frequency dynamics, which can induce the spillover instability. Furthermore, the parametric uncertainties on modal parameters can degrade the control performances and even destabilize the closed-loop system. In this context, a quantitative robust control methodology for active vibration control of flexible structure is proposed in this thesis. Phase and gain control polices are first proposed to enforce frequency-dependent phase and gain requirements on the controller, which can be realized by the output feedback H1 control design. The phase and gain control polices based H1 control can make a trade-off among the complete set of control objectives and offer a qualitative robust controller. Especially, the LPV H1 control is used to reduce the required control energy for LPV systems. The generalized polynomial chaos (gPC) framework with finite element analysis is employed for uncertainty quantification. It allows us to investigate the effects of structural property uncertainties on natural frequencies and achieve their probabilistic information. Then, in the presence of parametric and dynamic uncertainties, µ / v analysis and the random algorithm using Monte Carlo Method are used to quantitatively ensure the closed-loop stability and performance robustness properties both in deterministic and probabilistic senses. The proposed quantitative robust control methodology is thus developed by employing various techniques from automatic control and mechanical engineering, thus reducing the gap between them for robust vibration control of flexible structures. Its effectiveness are verified by numerical simulations and experimental validation on LTI and LPV non-collocated piezoelectric cantilever beams.

Les structures flexibles sont de plus en plus utilisées dans des domaines variés comme l'aérospatiale, l'automobile, etc. Les avantages du contrôle actif des vibrations sont son faible amortissement et sa sensibilité aux vibrations. Dans la réalité, en plus des exigences de réduction effective des vibrations, il faut également prendre en compte la quantité d'énergie nécessaire pour le contrôle, les entrées du contrôle pour éviter la saturation de commande, ainsi que la réduction des effets des bruits de mesure. D'autre part, comme les structures flexibles ont une infinité de modes de résonance et que seuls les premiers modes peuvent être utilisés dans la modélisation du système et dans la conception de contrôleur, les dynamiques négligées en hautes fréquences peuvent induire une instabilité dite "spill over". De plus, les incertitudes sur les paramètres modaux peuvent dégrader les performances de contrôle et même déstabiliser le système en boucle fermée. Dans ce contexte, on propose dans cette thèse une méthodologie quantitative de contrôle actif et robuste des vibrations des structures flexibles. Des stratégies de contrôle de la phase et du gain sont d'abord proposées pour assurer des spécifications dépendant de la fréquence sur la phase et le gain du contrôleur. Ces spécifications peuvent être réalisées par la conception du contrôleur par la méthode Hoo . Le contrôle H00 basé sur ces stratégies permet d'obtenir un compromis entre l'ensemble des objectifs de contrôle et d'offrir un contrôleur robuste qualitatif. En particulier, nous avons utilisé le contrôle LPV Hoo pour réduire l'énergie nécessaire au contrôle du système LPV. Le cadre généralisé du chaos polynomial (gPC) avec analyse par éléments finis, qui permet l'étude des effets des incertitudes de propriétés structurelles sur les fréquences naturelles et qui permet d'obtenir leurs informations probabilistes, est employé pour la quantification des incertitudes. Ensuite, en présence des incertitudes paramétriques et dynamiques, nous avons utilisé l'analyse 11/v et l'algorithme aléatoire en utilisant la méthode de Monte-Carlo pour assurer en même temps la stabilité en boucle fermée et les propriétés de robustesse de la performance à la fois dans le sens déterministe et le sens .probabiliste. La méthodologie de contrôle robuste quantitatif proposée est donc développée en employant des techniques diverses du contrôle automatique et du génie mécanique, et ainsi permet de réduire l'écart entre eux pour le contrôle robuste de la vibration pour des structures flexibles. Son efficacité est vérifiée par des simulations numériques et la validation expérimentale sur des poutres équipées de piézoélectriques non-colocalisés, LTI et LPV. / Flexible structures are increasingly used in various applications such as aerospace, automotive and so on. Since they are lightly damped and susceptible to vibrations, active vibration control is desirable. In practice, in addition to achieving effective vibration reduction, we have also to consider the required control energy to avoid the energy insufficiency, the control input to avoid control saturation and reduce the effects of measurement noises. On the other hand, as flexible structures have infinite number of resonant modes and only the first few can be employed in the system modeling and the controller design, there always exist neglected high-frequency dynamics, which can induce the spillover instability. Furthermore, the parametric uncertainties on modal parameters can degrade the control performances and even destabilize the closed-loop system. In this context, a quantitative robust control methodology for active vibration control of flexible structure is proposed in this thesis. Phase and gain control polices are first proposed to enforce frequency-dependent phase and gain requirements on the controller, which can be realized by the output feedback H1 control design. The phase and gain control polices based H1 control can make a trade-off among the complete set of control objectives and offer a qualitative robust controller. Especially, the LPV H1 control is used to reduce the required control energy for LPV systems. The generalized polynomial chaos (gPC) framework with finite element analysis is employed for uncertainty quantification. It allows us to investigate the effects of structural property uncertainties on natural frequencies and achieve their probabilistic information. Then, in the presence of parametric and dynamic uncertainties, µ / v analysis and the random algorithm using Monte Carlo Method are used to quantitatively ensure the closed-loop stability and performance robustness properties both in deterministic and probabilistic senses. The proposed quantitative robust control methodology is thus developed by employing various techniques from automatic control and mechanical engineering, thus reducing the gap between them for robust vibration control of flexible structures. Its effectiveness are verified by numerical simulations and experimental validation on LTI and LPV non-collocated piezoelectric cantilever beams.

The world is changing, what has been known to work has been put to the test when both the geopolitical and the environmental climate are changing. War, a pandemic, material shortage, financial difficulties and an overall dis- tressed global transportation sector have shown that the ever-more important topic of resilience is crucial to stay relevant in today’s competitive markets. Companies are therefore switching focus towards ensuring sufficient supply chain resilience capabilities to handle these ever-changing situations on the global market.  In this thesis, we focus on how Volvo SML is working with resilience today, and how graph theory and optimisation can be useful tools when analysing a supply chain’s resilience. We made a qualitative analysis by conducting inter- views with employees and comparing our findings with capabilities related to resilience. In addition, we conducted a quantitative analysis by constructing a simulation of the supply chain, comparing two topology metrics and two op- timisation metrics, to analyse the robustness of the aftermarket supply chain.  We analysed the data and summarised the insights gathered from the inter- views using a resilience capability framework. Volvo SML proved to be agile and reactive when dealing with disruptions but is missing some key capabil- ities during the pre-and post-disruption phases. Some areas of improvement we identified were: robustness, collaboration and redundancy. We proved that the simulation is useful when evaluating the robustness of a supply chain, and we showed that a more flexible way of working would improve the overall robustness of Volvo SML’s aftermarket supply chain.

As robustness of social science is getting more attention, analytical choices have been found to be more important than previously thought. This thesis investigates robustness of intergenerational educational mobility estimates using multiverse analysis, a technique for incorporating many analyses into one framework while varying analytical choices such as variable coding, mobility measures, and exclusion criteria. Using ESS data from 16 European countries over nine survey rounds, results show substantial variation in point estimates, which in turn creates high variation in rankings of European countries. The conclusion is that analytical choices play an important role in calculating educational mobility estimates, and that ranking of European countries according to intergenerational mobility estimates is sensitive to varying these choices. Future mobility research should take this into account.

Cette thèse vise à améliorer le positionnement statique et la précision de suivi de trajectoire des Robots Parallèles à Câbles (RPC) tout en prenant en compte leur élasticité globale. A cet effet, deux stratégies de commandes complémentaires valables pour toute configuration de RPC sont proposées.Tout d'abord, une analyse de robustesse est réalisée pour aboutir à une commande robuste des RPC référencée modèle. Un modèle de RPC approprié est défini en fonction de l'application visée et les principales sources d'erreurs de pose de la plate-forme mobile sont identifiées.Une première méthode de commande est proposée sur la base des résultats de l'analyse de robustesse. Cette première méthode réside dans le couplage d'une commande référencée modèle d’un contrôleur PID.Dans le cadre de cette thèse, un modèle élasto-dynamique de RPC est exprimé afin de compenser le comportement oscillatoire de sa plate-forme mobile dû à l'élongation des câbles et de son comportement dynamique.La deuxième méthode de commande utilise des filtres "input-shaping" dans la commande référencée modèle proposée afin d'annuler les mouvements oscillatoires de la plate-forme mobile. Ainsi, le signal d'entrée est modifié pour que le RPC annule automatiquement les vibrations résiduelles. Les résultats théoriques obtenus sont validés expérimentalement à l'aide d'un prototype de RPC non redondant en actionnement et en configuration suspendue. Les résultats expérimentaux montrent la pertinence des stratégies de commande proposées en termes d'amélioration de la précision de suivi de trajectoire et de réduction des vibrations. / This thesis aims at improving the static positioning and trajectory tracking accuracy of Cable- Driven Parallel Robots (CDPRs) while considering their overall elasticity. Accordingly, two complementary control strategies that are valid for any CDPR configuration are proposed.First, a robustness analysis is performed to lead to a robust model-based control of CDPRs. As a result, an appropriate CDPR model is defined as a function of the targeted application and the main sources of CDPR moving-platforms pose errors are identified.A first control method is determined based on the results of the robustness analysis. This first method lies in the coupling of a model-based feed-forward control scheme for CDPR with a PID feedback controller.Here, an elasto-dynamic model of the CDPR is expressed to compensate the oscillatory motions of its moving-platform due to cable elongations and its dynamic behavior.The second control method uses input-shaping filters into the proposed model-based feed-forward control in order to cancel the oscillatory motions the movingplatform. Thus, the input signal is modified for the CDPR to self-cancel residual vibrations.Experimental validations are performed while using suspended and non-redundant CDPR prototype. The proposed feed-forward model-based control schemes are implemented, and their effectiveness is discussed.Results show the relevance of the proposed control strategies in terms of trajectory tracking accuracy improvement and vibration reduction.