Secure Routing Optimization in Hierarchical Cluster-Based Wireless Sensor Networks

Popularity of wireless sensor networks (WSNs) is increasing continuously in different domains of daily life, as they provide efficient method of collecting valuable data from the surroundings for use in different applications. Routing in WSNs is the vital functionality that allows the flow of information generated by sensor nodes to the base station, while considering the severe energy constraint and the limitations of computational and storage resources. Indeed, this functionality may be vulnerable and must be in itself secured, since conventional routing protocols in WSNs provide efficient routing techniques with low power consumption, but they do not take into account the possible attacks. As sensor nodes may be easily captured and compromised, the classical cryptographic solutions become insufficient to provide optimal routing security, especially, for cluster-based WSNs, where cluster heads can be still among the compromised nodes. In this work, we propose a hierarchical, robust and well-adapted intrusion detection system, named THIDS, which is intended to be integrated into the secure hierarchical cluster-based routing protocols. We have chosen the protocol RLEACH to be equipped with the proposed IDS. The results of simulation performed under NS2 simulator show that the resulting protocol ORLEACH is much more resistant to compromised nodes exercising the most dangerous attacks

Brute-Force Cryptanalysis with Aging Hardware: Controlling Half the Output of SHA-256

This paper describes a "three-way collision" on SHA-256 truncated to 128 bits. More precisely, it gives three random-looking bit strings whose hashes by SHA-256 maintain a non-trivial relation: their XOR starts with 128 zero bits. They have been found by brute-force, without exploiting any cryptographic weakness in the hash function itself. This shows that birthday-like computations on 128 bits are becoming increasingly feasible, even for academic teams without substantial means. These bit strings have been obtained by solving a large instance of the three-list generalized birthday problem, a difficult case known as the 3XOR problem. The whole computation consisted of two equally challenging phases: assembling the 3XOR instance and solving it. It was made possible by the combination of: 1) recent progress on algorithms for the 3XOR problem, 2) creative use of "dedicated" hardware accelerators, 3) adapted implementations of 3XOR algorithms that could run on massively parallel machines. Building the three lists required 2 67.6 evaluations of the compression function of SHA-256. They were performed in 7 calendar months by two obsolete secondhand bitcoin mining devices, which can now be acquired on eBay for about 80e. The actual instance of the 3XOR problem was solved in 300 CPU years on a 7-year old IBM Bluegene/Q computer, a few weeks before it was scrapped. To the best of our knowledge, this is the first explicit 128-bit collision-like result for SHA-256. It is the first bitcoin-accelerated cryptanalytic computation and it is also one of the largest public ones

Instabilités aux grandes ondes d'écoulements axisymétriques coaxiaux

Nous présentons un modèle théorique décrivant l'écoulement par gravité de deux fluides immiscibles à l'intérieur d'une conduite cylindrique. Un développement en gradient combiné à une méthode de Galerkin est utilisé pour réduire le problème à un système de deux équations d'évolution de l'interface. Les prédictions de l'étude de stabilité linéaire sont en bon accord avec les données disponibles dans la littérature

IMPLEMENTATION AND OPTIMIZATION OF RWP MOBILITY MODEL IN WSNS UNDER TOSSIM SIMULATOR

Mobility has always represented a complicated phenomenon in the network routing process. This complexity is mainly facilitated in the way that ensures reliable connections for efficient orientation of data. Many years ago, different studies were initiated basing on routing protocols dedicated to static environments in order to adapt them to the mobile environment. In the present work, we have a different vision of mobility that has many advantages due to its 'mobile' principle. Indeed, instead of searching to prevent mobility and testing for example to immobilize momentarily a mobile environment to provide routing task, we will exploit this mobility to improve routing. Based on that, we carried out a set of works to achieve this objective. For our first contribution, we found that the best way to make use of this mobility is to follow a mobility model. Many models have been proposed in the literature and employed as a data source in most studies. After a careful study, we focused on the Random Waypoint mobility model (RWP) in order to ensure routing in wireless networks. Our contribution involves a Random Waypoint model (in its basic version) that was achieved on the TOSSIM simulator, and it was considered as a platform for our second (and main) contribution, in which we suggested an approach based RWP where network nodes can collaborate and work together basing on our recommended algorithm. Such an approach offers many advantages to ensure routing in a dynamic environment. Finally, our contributions comprise innovative ideas for suggesting other solutions that will improve them

Modélisation d'instabilités de films tombants en présence d'un champ électromagnétique

Un modèle analytique simple a été développé pour décrire les instabilités à l'interface fluide-air d'un écoulement axisymétrique dans une conduite cylindrique. Les fluides en écoulement sont newtoniens et incompressibles. La technique suivie combine une méthode aux résidus pondérés à un développement aux grandes longueurs des champs de vitesses. L'influence de différents paramètres (diamètre de la conduite, intensité du champ électomagnétique...) sur le taux de croissance des perturbations a été examinée via une étude de stabilité linéaire

Ondes de surface dans l'écoulement d'un fluide électroconducteur à l'intérieur d'une conduite cylindrique

Dans ce travail, nous nous sommes intéressés à l'écoulement en présence d'un champ électromagnétique d'un film mince d'un fluide visqueux supposé incompressible. Le fluide s'écoule à l'intérieur d'une conduite cylindrique verticale. La méthode de calcul utilisée est celle de Galerkin. Comme fonctions tests, nous avons choisi un profil similaire à celui de l'écoulement de base, il est de type logarithmique. L'influence du champ électromagnétique sur la stabilité de la surface libre a été examinée à travers une étude de stabilité linéaire

Modélisation d'un film mince viscoélastique en écoulement sur une paroi cylindrique verticale

Our interest is to model the long wavelength instability in a two dimensional flow of a thin viscoelastic fluid film flowing down a vertical cylinder under gravity. The effects of surface tension are included. A weighted residual integral method obtains a nonlinear evolution equation of the film interface and the flow rate, which is completed by a mass conservation equation. A normal mode approach is used to obtain the linear stability solutions for the film flow. It is shown that for certain ranges of the controlling dimensionless parameters the long wave instability is a capillary instability. The influence of viscoelastic parameter and curvature on the neutral stability diagrams for this instability are investigated

Diagrammes de stabilité d'un écoulement coaxial de deux fluides viscoélastiques

Dans ce travail, notre objectif est de présenter une étude sur l'instabilité de l'interface entre deux couches de fluides viscoélastiques incompressibles s'écoulant à l'intérieur d'un cylindre. Une équation gouvernant la dynamique de l'écoulement est obtenue en utilisant une méthode de développement asymptotique pour résoudre les équations de Navier-Stokes et des conditions aux limites associées. Cette approche est valable aux ondes interfaciales qui sont longues par rapport aux épaisseurs des couches fluides et permet de déterminer avec précision les conditions d'apparition des instabilités à l'interface. Les résultats obtenus dans ce cadre, nous permettent de mettre en évidence l'influence des nombreux paramètres du problème sur le nombre de Reynolds critique

Eradication of an outbreak of vancomycin-resistant Enterococcus (VRE): the cost of a failure in the systematic screening

BACKGROUND: Vancomycin-resistant enterococci (VRE) are still a concern in hospital units tending to seriously ill patients. However, the cost-effectiveness of active surveillance program to identify asymptomatically VRE colonized patient remains debatable. This work aims at evaluating the cost of a failure in the active surveillance of VRE that had resulted in an outbreak in a French University Hospital. FINDINGS: A VRE outbreak was triggered by a failure in the systematic VRE screening in a medico-surgical ward specialised in liver transplantation as a patient was not tested for VRE. This failure was likely caused by the reduction of healthcare resource. The outbreak involved 13 patients. Colonized patients were grouped in a dedicated part of the infectious diseases unit and tended by a dedicated staff. Transmission was halted within two months after discovery of the index case. The direct cost of the outbreak was assessed as the cost of staffing, disposable materials, hygiene procedures, and surveillance cultures. The loss of income from spare isolation beds was computed by difference with the same period in the preceding year. Payments were drawn from the hospital database. The direct cost of the outbreak (2008 Euros) was €60 524 and the loss of income reached €110 915. CONCLUSIONS: Despite this failure, the rapid eradication of the VRE outbreak was a consequence of the rapid isolation of colonized patient. Yet, eradicating even a limited outbreak requires substantial efforts and resources. This underlines that special attention has to be paid to strictly adhere to active surveillance program

Computational Records with Aging Hardware: Controlling Half the Output of SHA-256

SHA-256 is a secure cryptographic hash function. As such, its output should not have any detectable property. This paper describes three bit strings whose hashes by SHA-256 are nevertheless correlated in a non-trivial way: the first half of their hashes XORs to zero. They were found by “brute-force”, without exploiting any cryptographic weakness in the hash function itself. This does not threaten the security of the hash function and does not have any cryptographic implication. This is an example of a large “combinatorial” computation in which at least 8.7 × 10 22 integer operations have been performed. This was made possible by the combination of: 1) recent progress on algorithms for the underlying problem, 2) creative use of dedicated hardware accelerators, 3) adapted implementations of the relevant algorithms that could run on massively parallel machines. The actual computation was done on aging hardware. It required seven calendar months using two obsolete second-hand bitcoin mining devices converted into useful computational devices. A second step required 570 CPU-years on an 8-year old IBM BlueGene/Q computer, a few weeks before it was scrapped. To the best of our knowledge, this is the first practical 128-bit collision-like result obtained by brute-force, and it is the first bitcoin miner-accelerated computation