Content Censorship in the InterPlanetary File System

The InterPlanetary File System (IPFS) is currently the largest decentralized storage solution in operation, with thousands of active participants and millions of daily content transfers. IPFS is used as remote data storage for numerous blockchain-based smart contracts, Non-Fungible Tokens (NFT), and decentralized applications. We present a content censorship attack that can be executed with minimal effort and cost, and that prevents the retrieval of any chosen content in the IPFS network. The attack exploits a conceptual issue in a core component of IPFS, the Kademlia Distributed Hash Table (DHT), which is used to resolve content IDs to peer addresses. We provide efficient detection and mitigation mechanisms for this vulnerability. Our mechanisms achieve a 99.6\% detection rate and mitigate 100\% of the detected attacks with minimal signaling and computational overhead. We followed responsible disclosure procedures, and our countermeasures are scheduled for deployment in the future versions of IPFS.Comment: 15 pages (including references), 15 figures. Accepted to be published at the Network and Distributed System Security (NDSS) Symposium 202

Neural correlates of impaired cognitive processes underlying self-unawareness in Alzheimer’s disease

peer reviewe

Staphylococcus aureus infective endocarditis versus bacteremia strains: Subtle genetic differences at stake

AbstractInfective endocarditis (IE)(1) is a severe condition complicating 10–25% of Staphylococcus aureus bacteremia. Although host-related IE risk factors have been identified, the involvement of bacterial features in IE complication is still unclear. We characterized strictly defined IE and bacteremia isolates and searched for discriminant features. S. aureus isolates causing community-acquired, definite native-valve IE (n=72) and bacteremia (n=54) were collected prospectively as part of a French multicenter cohort. Phenotypic traits previously reported or hypothesized to be involved in staphylococcal IE pathogenesis were tested. In parallel, the genotypic profiles of all isolates, obtained by microarray, were analyzed by discriminant analysis of principal components (DAPC)(2). No significant difference was observed between IE and bacteremia strains, regarding either phenotypic or genotypic univariate analyses. However, the multivariate statistical tool DAPC, applied on microarray data, segregated IE and bacteremia isolates: IE isolates were correctly reassigned as such in 80.6% of the cases (C-statistic 0.83, P<0.001). The performance of this model was confirmed with an independent French collection IE and bacteremia isolates (78.8% reassignment, C-statistic 0.65, P<0.01). Finally, a simple linear discriminant function based on a subset of 8 genetic markers retained valuable performance both in study collection (86.1%, P<0.001) and in the independent validation collection (81.8%, P<0.01). We here show that community-acquired IE and bacteremia S. aureus isolates are genetically distinct based on subtle combinations of genetic markers. This finding provides the proof of concept that bacterial characteristics may contribute to the occurrence of IE in patients with S. aureus bacteremia

Magnetostatic and Magnetodynamic Mixed Formulations Compared with Conventional Formulations

Mixed formulations are characterized by the use, of not only one kind of unknown, but of two distinct kinds of unknowns. Some well-known mixed finite elements are well suited to the approximation of electromagnetic fields. Several characteristics of magnetostatic and magnetodynamic mixed formulations are presented and discussed. The use of nodal, edge, facet and volume mixed elements enables their natural and rigorous discretization. Their advantages compared with conventional formulations are pointed out

On the Resolution of Magnetostatic and Magnetodynamic Mixed Formulations

Mixed formulations of Maxwell's equations are presented and the nature of the matrices appearing in these formulations is discussed. Their indefinite character is discussed. A method for solving these unusual matrices is then developed and applied to a test problem

A posteriori error estimation and adaptive meshing using error in constitutive relation

The paper presents a method to control the quality of finite element solutions error in the constitutive relation. An a posteriori estimator is built up. Its construction is general and gives quantitative results about the accuracy of the solution. Both problems of control of quality and mesh optimisation are also discussed. Several examples are presented. A method used to compute a magnetic field that verifies Ampere's law using only local calculations is presented

Determination of equivalent material characteristics for parasitic effects in electrical apparatus

For linear systems excited with sinusoidal constraints, an exact dynamical modelling can be performed with a phasor (complex number) approach. For nonlinear systems (exhibiting saturation, hysteresis and higher harmonics), a time stepping model is very time consuming. A method to model such nonlinear systems with an approximated phasor approach is presented. Determination of equivalent material characteristics is discussed and applications are given

A Generalized Source Magnetic Field Calculation Method for Inductors of any Shape

A general method to compute source fields in magnetostatics or magnetodynamics is presented for inductors of any shape. That source field is not the physical one because the zero divergence condition is not satisfied. However, the freedom so obtained is exploited to minimize its support as well as to reduce the CPU time. The use of edge finite elements enables its rigorous construction. A test problem illustrates the method

Une méthode naturelle de traitement des potentiels flottants associée à la méthode des éléments finis

peer reviewedUne méthode efficace de traitement des potentiels flottants, utilisée dans le cadre de la méthode des éléments finis et appliquée au problème de l'électrostatique, est présentée. De plus, cette méthode conduit à une technique pour l'évaluation de la charge électrique, technique qui se base sur un calcul moyenné en accord parfait avec la formulation faible discrétisée du problème. La méthode générale offre alors l'avantage de donner directement accès, lors du calcul, aux charges électriques totales des conducteurs à potentiels fixés ou flottants, tout en préservant le caractère symétrique de la matrice du système, ce qui permet un couplage aisé entre charges et potentiels tant au niveau de la formulation qu'au niveau de la résolution. Elle permet ainsi d'aborder tout problème électrostatique sans aucune technique intermédiaire de calcul, par exemple de différentiation

Modelling of Inductive Effects in Thin Wire Coils

In conducting media, inductive effects give rise to eddy currents that produce skin effect and proximity effect. In thin wire coils in which the inductive effects are present the current density is forced to remain constant in the coil if the skin depth is larger than the characteristic size of the wire. This paper presents a homogenization technique based on the finite element method, to take into account thin wire coils in two-dimensional dynamic magnetic field computations