Dégradation de données par publication éphémère

Le respect de la vie privée est un droit fondamental mais difficile à garantir sur Internet. Malgré les recommandations des experts, le principe de minimisation des données -- qui exige notamment que les données soient effacées aussitôt qu'elles ne sont plus strictement nécessaires (rétention minimale) -- est rarement appliqué, en raison d'intérêts divergents entre les hébergeurs des données personnelles et les utilisateurs. Pour diminuer l'impact de ces divergences, une alternative à la rétention minimale a été proposée, la dégradation des données : au lieu d'être complètement effacée, une donnée peut être progressivement dégradée vers des états moins précis qui protègent mieux la vie privée de l'utilisateur tout en conservant (partiellement) l'utilité de la donnée initiale. Cependant, aucune architecture n'existe à l'heure actuelle qui garantisse la dégradation des données sans un gestionnaire de base de données de confiance. En utilisant un système de publication éphémère (une donnée ne peut plus être accédée après une date d'expiration fixée à l'avance), nous proposons dans ce travail une architecture décentralisée qui garantit la dégradation des données sans aucun acteur de confiance dans le système

Ambient and substrate energy influence decomposer diversity differentially across trophic levels

The species-energy hypothesis predicts increasing biodiversity with increasing energy in ecosystems. Proxies for energy availability are often grouped into ambient energy (i.e., solar radiation) and substrate energy (i.e., non-structural carbohydrates or nutritional content). The relative importance of substrate energy is thought to decrease with increasing trophic level from primary consumers to predators, with reciprocal effects of ambient energy. Yet, empirical tests are lacking. We compiled data on 332,557 deadwood-inhabiting beetles of 901 species reared from wood of 49 tree species across Europe. Using host-phylogeny-controlled models, we show that the relative importance of substrate energy versus ambient energy decreases with increasing trophic levels: the diversity of zoophagous and mycetophagous beetles was determined by ambient energy, while non-structural carbohydrate content in woody tissues determined that of xylophagous beetles. Our study thus overall supports the species-energy hypothesis and specifies that the relative importance of ambient temperature increases with increasing trophic level with opposite effects for substrate energy

Ambient and substrate energy influence decomposer diversity differentially across trophic levels.

The species-energy hypothesis predicts increasing biodiversity with increasing energy in ecosystems. Proxies for energy availability are often grouped into ambient energy (i.e., solar radiation) and substrate energy (i.e., non-structural carbohydrates or nutritional content). The relative importance of substrate energy is thought to decrease with increasing trophic level from primary consumers to predators, with reciprocal effects of ambient energy. Yet, empirical tests are lacking. We compiled data on 332,557 deadwood-inhabiting beetles of 901 species reared from wood of 49 tree species across Europe. Using host-phylogeny-controlled models, we show that the relative importance of substrate energy versus ambient energy decreases with increasing trophic levels: the diversity of zoophagous and mycetophagous beetles was determined by ambient energy, while non-structural carbohydrate content in woody tissues determined that of xylophagous beetles. Our study thus overall supports the species-energy hypothesis and specifies that the relative importance of ambient temperature increases with increasing trophic level with opposite effects for substrate energy

Arthropod communities in fungal fruitbodies are weakly structured by climate and biogeography across European beech forests

Aim The tinder fungus Fomes fomentarius is a pivotal wood decomposer in European beech Fagus sylvatica forests. The fungus, however, has regionally declined due to centuries of logging. To unravel biogeographical drivers of arthropod communities associated with this fungus, we investigated how space, climate and habitat amount structure alpha and beta diversity of arthropod communities in fruitbodies of F. fomentarius. Location Temperate zone of Europe. Taxon Arthropods. Methods We reared arthropods from fruitbodies sampled from 61 sites throughout the range of European beech and identified 13 orders taxonomically or by metabarcoding. We estimated the total number of species occurring in fruitbodies of F. fomentarius in European beech forests using the Chao2 estimator and determined the relative importance of space, climate and habitat amount by hierarchical partitioning for alpha diversity and generalized dissimilarity models for beta diversity. A subset of fungi samples was sequenced for identification of the fungus’ genetic structure. Results The total number of arthropod species occurring in fruitbodies of F. fomentarius across European beech forests was estimated to be 600. Alpha diversity increased with increasing fruitbody biomass; it decreased with increasing longitude, temperature and latitude. Beta diversity was mainly composed by turnover. Patterns of beta diversity were only weakly linked to space and the overall explanatory power was low. We could distinguish two genotypes of F. fomentarius, which showed no spatial structuring. Main conclusion Fomes fomentarius hosts a large number of arthropods in European beech forests. The low biogeographical and climatic structure of the communities suggests that fruitbodies represent a habitat that offers similar conditions across large gradients of climate and space, but are characterized by high local variability in community composition and colonized by species with high dispersal ability. For European beech forests, retention of trees with F. fomentarius and promoting its recolonization where it had declined seems a promising conservation strategy

Climate-induced forest dieback drives compositional changes in insect communities that are more pronounced for rare species

Species richness, abundance and biomass of insects have recently undergone marked declines in Europe. We metabarcoded 211 Malaise-trap samples to investigate whether drought-induced forest dieback and subsequent salvage logging had an impact on ca. 3000 species of flying insects in silver fir Pyrenean forests. While forest dieback had no measurable impact on species richness, there were significant changes in community composition that were consistent with those observed during natural forest succession. Importantly, most observed changes were driven by rare species. Variation was explained primarily by canopy openness at the local scale, and the tree-related microhabitat diversity and deadwood amount at landscape scales. The levels of salvage logging in our study did not explain compositional changes. We conclude that forest dieback drives changes in species assemblages that mimic natural forest succession, and markedly increases the risk of catastrophic loss of rare species through homogenization of environmental conditions

Vers une construction holistique des systèmes distribués opportunistes à large échelle

With the advent of the IoT, Smart Cities, and other large-scale extremely heterogeneous systems, distributed systems are becoming both more complex and pervasive every day and will soon be intractable with current approaches. To hide this growing complexity and facilitate the management of distributed systems at all stages of their life-cycle, this thesis argues for a holistic approach, where the function of a system is considered as a whole, moving away from the behavior of individual components. In parallel to this rise in abstraction levels, basic building blocks need to become more autonomous and able to react to circumstances, to alleviate developers and automate most of the low level operations. We propose three contributions towards this vision : 1) Pleiades: a holistic approach to build complex structures by assembly, easily programmable and supported by an efficient, self-organizing gossip-based run-time engine. 2) Mind-the-Gap: a gossip-based protocol to detect partitions and other large connectivity changes in MANETs, thanks to periodic opportunistic aggregations and a stochastic representation of the network membership. 3) HyFN: an extension to traditional gossip protocols that is able to efficiently solve the k-Furthest-Neighbors problem, which standard methods have been unable to up to now. We believe these three contributions demonstrate our vision is realistic and highlight its attractive qualities.Avec le développement de l'IoT, des Smart Cities, et d'autres systèmes large-échelle extrêmement hétérogènes, les systèmes distribués deviennent à la fois plus complexes et plus omniprésents de jour en jour et seront bientôt difficiles à gérer avec les approches courantes. Pour masquer cette difficulté croissante et faciliter leur gestion à tous les stages de leur cycle de vie, cette thèse soutient qu'une approche holistique est nécessaire, où la fonction d'un système est considérée comme un tout, et qui se détache du comportement des composants individuels. En parallèle à cette montée en abstraction, les blocs de base doivent devenir plus autonomes, capable de réagir aux circonstances et d'automatiser la plupart des tâches de bas niveau. Nous proposons trois contributions vers cette vision : 1) Pleiades : une approche holistique pour construire des structures complexes par assemblage, facile à programmer et soutenue par un moteur d'exécution auto-organisant et efficace, basé sur des protocoles épidémiques. 2) Mind-the-Gap : un protocole épidémique de détection des partitions dans les MANETs, grâce à des agrégations opportunistes et à une représentation stochastique compacte du réseau. 3) HyFN: une extension des protocoles épidémiques traditionnels, capable de résoudre efficacement le problème des k-plus-lointains-voisins, ce dont les méthodes standards s'étaient révélées incapables jusqu'à maintenant. Nous considérons que ces trois contributions montrent que notre vision est réaliste, et mettent en valeur ses qualités

Implémenter le droit à l'oubli

Le respect de la vie privée est un droit fondamental mais difficile à protéger dans un monde numérique : copier et transmettre de l'information est devenu extrêmement simple. Aussi, le droit à l'oubli est-il une composante de plus en plus importante de la protection de la vie privée. Toutefois, une solution technique et complète pour implémenter le droit à l'oubli paraît impossible à l'heure actuelle. Nous présentons donc les systèmes existants et leurs domaines d'applications respectifs. Leur mise en œuvre se heurte cependant à des intérêts contradictoires entre utilisateurs et hébergeurs des données, qui engendrent un manque de confiance. Puis, nous introduisons le mécanisme de dégradation des données qui recoupe les principes de rétention et de collecte minimales et qui permet, combiné à une technique de publication éphémère, de réconcilier partiellement les intérêts des hébergeurs et des utilisateurs et de passer outre les problèmes. Enfin, nous présentons une architecture générale utilisant ces deux mécanismes ainsi qu'une illustration sur le cas d'un réseau géo-social

Polystyrene: the Decentralized Data Shape That Never Dies

International audienceDecentralized topology construction protocols organize nodes along a predefined topology (e.g. a torus, ring, or hypercube). Such topologies have been used in many contexts ranging from routing and storage systems, to publish-subscribe and event dissemination. Since most topologies assume no correlation between the physical location of nodes and their positions in the topology, they do not handle catastrophic failures well, in which a whole region of the topology disappears. When this occurs, the overall shape of the system typically gets lost. This is highly problematic in applications in which overlay nodes are used to map a virtual data space, be it for routing, indexing or storage. In this paper, we propose a novel decentralized approach that maintains the initial shape of the topology even if a large (consecutive) portion of the topology fails. Our approach relies on the dynamic decoupling between physical nodes and virtual ones enabling a fast reshaping. For instance, our results show that a 51,200-node torus converges back to a full torus in only 10 rounds after 50% of the nodes have crashed. Our protocol is both simple and flexible and provides a novel form of collective survivability that goes beyond the current state of the art

Scalable Anti-KNN: Decentralized Computation of k-Furthest-Neighbor Graphs with HyFN

Part 3: Roaming in Graph (Graph Processing)International audienceThe decentralized construction of k-Furthest-Neighbor graphs has been little studied, although such structures can play a very useful role, for instance in a number of distributed resource allocation problems. In this paper we define KFN graphs; we propose HyFN, a generic peer-to-peer KFN construction algorithm, and thoroughly evaluate its behavior on a number of logical networks of varying sizes. 1 Motivation k-Nearest-Neighbor (KNN) graphs have found usage in a number of domains, including machine learning, recommenders, and search. Some applications do not however require the k closest nodes, but the k most dissimilar nodes, what we term the k-Furthest-Neighbor (KFN) graph. Virtual Machines (VMs) placement —i.e. the (re-)assignment of workloads in virtualised IT environments— is a good example of where KFN can be applied. The problem consists in finding an assignment of VMs on physical machines (PMs) that minimises some cost function(s) [27]. The problem has been described as one of the most complex and important for the IT industry [3], with large potential savings [20]. An important challenge is that a solution does not only consist in packing VMs onto PMs — it also requires to limit the amount of interferences between VMs hosted on the same PM [31]. Whatever technique is used (e.g. clustering [21]), interference aware VM placement algorithms need to identify complementary workloads — i.e. workloads that are dissimilar enough that the interferences between them are minimised. This is why the application of KFN graphs would make a lot of sense: identifying quickly complementary workloads (using KFN) to help placement algorithms would decrease the risks of interferences. The construction of KNN graphs in decentralized systems has been widely studied in the past [17, 30, 4, 14]. However, existing approaches typically assume a form of " likely transitivity " of similarity between nodes: if A is close to B, and B to C, then A is likely to be close to C. Unfortunately this property no longer holds when constructing KFN graphs. As a result, these approaches, as demonstrated in the remainder of the paper, are not working anymore when applied to this new problem

Key Update for the IoT Security Standard OSCORE

The standard Constrained Application Protocol (CoAP) is a lightweight, web-transfer protocol based on the REST paradigm and specifically suitable for constrained devices and the Internet-of-Things. Object Security for Constrained RESTful Environment (OSCORE) is a standard, lightweight security protocol that provides end-to-end protection of CoAP messages. A number of methods exist for managing keying material for OSCORE, as to its establishment and update. This paper provides a detailed comparison of such methods, in terms of their features, limitations and security properties. Also, it especially considers the new key update protocol KUDOS, for which it provides a more extended discussion about its features and mechanics, as well as a formal verification of its security properties.SIFIS-HomeSEC4FactoryARCADIAN-Io