1,032 research outputs found

    An Implementation of Distance-Based Message Authentication for WSNs

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    Distance-Based Message Authentication (DBMA) provides an additional layer of access control and helps to defend against key compromise and denial-of-service attacks on constrained nodes. The distance between sender and receiver is measured securely. Messages sent from outside a defined physical distance can be rejected early, protecting vulnerable higher layers. We show our initial implementation using the Nanotron NA5TR1. We show how changing MAC addresses can avoid modification to ranging hardware

    Migration of massive black hole binaries in self--gravitating accretion discs: Retrograde versus prograde

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    We study the interplay between mass transfer, accretion and gravitational torques onto a black hole binary migrating in a self-gravitating, retrograde circumbinary disc. A direct comparison with an identical prograde disc shows that: (i) because of the absence of resonances, the cavity size is a factor a(1+e) smaller for retrograde discs; (ii) nonetheless the shrinkage of a circular binary semi--major axis, a, is identical in both cases; (iii) a circular binary in a retrograde disc remains circular while eccentric binaries grow more eccentric. For non-circular binaries, we measure the orbital decay rates and the eccentricity growth rates to be exponential as long as the binary orbits in the plane of its disc. Additionally, for these co-planar systems, we find that interaction (~ non--zero torque) stems only from the cavity edge plus a(1+e) in the disc, i.e. for dynamical purposes, the disc can be treated as a annulus of small radial extent. We find that simple 'dust' models in which the binary- disc interaction is purely gravitational can account for all main numerical results, both for prograde and retrograde discs. Furthermore, we discuss the possibility of an instability occurring for highly eccentric binaries causing it to leave the disc plane, secularly tilt and converge to a prograde system. Our results suggest that there are two stable configurations for binaries in self-gravitating discs: the special circular retrograde case and an eccentric (e~ 0.6) prograde configuration as a stable attractor.Comment: 14 pages, 2 Tabes, 11 Figures, submitted to MNRAS, comments welcom

    Origin and Implications of high eccentricities in massive black hole binaries at sub-pc scales

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    We outline the eccentricity evolution of sub-parsec massive black hole binaries (MBHBs) forming in galaxy mergers. In both stellar and gaseous environments, MBHBs are expected to grow large orbital eccentricities before they enter the gravitational wave (GW) observational domain. We re--visit the predicted eccentricities detectable by space based laser interferometers (as the proposed ELISA/NGO) for both environments. Close to coalescence, many MBHBs will still maintain detectable eccentricities, spanning a broad range from <10^{-5} up to <~ 0.5. Stellar and gas driven dynamics lead to distinct distributions, with the latter favoring larger eccentricities. At larger binary separations, when emitted GWs will be observed by pulsar timing arrays (PTAs), the expected eccentricities are usually quite large, in the range 0.01-0.7, which poses an important issue for signal modelling and detection algorithms. In this window, large eccentricities also have implications on proposed electromagnetic counterparts to the GW signal, which we briefly review.Comment: AMALDI9 proceedings, submitted to CQG ; 10 Pages 2 Figure

    Optimized usage of network resources based on context information

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    Today an efficient (cost-effective) design and usage of networks is of particular importance. As more and more computer systems become context-aware the question of how context information can be used to improve computer networks arises. In this poster we describe how context information can be used to optimize the usage of resources in a computer network. By means of a mobile payment system we show how these optimization method can be applied

    Evaluating and improving firewalls for ip-telephony environments

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    Firewalls are a well established security mechanism for providing access control and auditing at the borders between different administrative network domains. Their basic architecture, techniques and operation modes did not change fundamentally during the last years. On the other side new challenges emerge rapidly when new innovative application domains have to be supported. IP-Telephony applications are considered to have a huge economic potential in the near future. For their widespread acceptance and thereby their economic success they must cope with established security policies. Existing firewalls face immense problems here, if they - as it still happens quite often - try to handle the new challenges in a way they did with "traditional applications". As we will show in this paper, IP-Telephony applications differ from those in many aspects, which makes such an approach quite inadequate. After identifying and characterizing the problems we therefore describe and evaluate a more appropriate approach. The feasibility of our architecture will be shown. It forms the basis of a prototype implementation, that we are currently working on

    Demo Abstract: Securing Communication in 6LoWPAN with Compressed IPsec

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    With the inception of IPv6 it is possible to assign a unique ID to each device on planet. Recently, wireless sensor networks and traditional IP networks are more tightly integrated using IPv6 and 6LoWPAN. Real-world deployments of WSN demand secure communication. The receiver should be able to verify that sensor data is generated by trusted nodes and/or it may also be necessary to encrypt sensor data in transit. Available IPv6 protocol stacks can use IPsec to secure data exchanges. Thus, it is desirable to extend 6LoWPAN such that IPsec communication with IPv6 nodes is possible. It is beneficial to use IPsec because the existing end-points on the Internet do not need to be modified to communicate securely with the WSN. Moreover, using IPsec, true end-to-end security is implemented and the need for a trustworthy gateway is removed. In this demo we will show the usage of our implemented lightweight IPsec. We will show how IPsec ensures end-to-end security between an IP enabled sensor networks and the traditional Internet. This is the first compressed lightweight design, implementation, and evaluation of a 6LoWPAN extension for IPsec. This demo complements the full paper that will appear in the parent conference, DCOSS’11

    Network Coding with Limited Overhearing

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    The two key benefits of network coding are increased reliability and throughput. Most network coding approaches for wireless networks rely on overhearing neighboring transmissions. Overhearing in sensor networks, however, is not energy-efficient. In this paper, we extend GinMAC, a state-of-the-art MAC protocol, applying network coding with limited overhearing. Our approach reduces the delay allocating less retransmission slots. Our results show that network coding with limited overhearing reduces the power consumption of GinMAC while maintaining the desired level of reliability
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