1,032 research outputs found
An Implementation of Distance-Based Message Authentication for WSNs
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
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
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
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
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
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
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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