21,111 research outputs found
Random Permutation Statistics and An Improved Slide-Determine Attack on KeeLoq
KeeLoq is a lightweight block cipher which is extensively used in the automotive industry. Its periodic structure, and overall simplicity makes it vulnerable to many different attacks. Only certain attacks are considered as really "practical" attacks on KeeLoq: the brute force, and several other attacks which require up to 2p16 known plaintexts and are then much faster than brute force, developed by Courtois et al., and (faster attack) by Dunkelman et al. On the other hand, due to the unusually small block size, there are yet many other attacks on KeeLoq, which require the knowledge of as much as about 2p32 known plaintexts but are much faster still. There are many scenarios in which such attacks are of practical interest, for example if a master key can be recovered, see Section 2 in [11] for a detailed discussion. The fastest of these attacks is an attack by Courtois, Bard and Wagner from that has a very low complexity of about 2p28 KeeLoq encryptions on average. In this paper we will propose an improved and refined attack which is faster both on average and in the best case. We also present an exact mathematical analysis of probabilities that arise in these attacks using the methods of modern analytic combinatorics
Euler-Heisenberg lagrangians and asymptotic analysis in 1+1 QED, part 1: Two-loop
We continue an effort to obtain information on the QED perturbation series at
high loop orders, and particularly on the issue of large cancellations inside
gauge invariant classes of graphs, using the example of the l - loop N - photon
amplitudes in the limit of large photons numbers and low photon energies. As
was previously shown, high-order information on these amplitudes can be
obtained from a nonperturbative formula, due to Affleck et al., for the
imaginary part of the QED effective lagrangian in a constant field. The
procedure uses Borel analysis and leads, under some plausible assumptions, to a
number of nontrivial predictions already at the three-loop level. Their direct
verification would require a calculation of this `Euler-Heisenberg lagrangian'
at three-loops, which seems presently out of reach. Motivated by previous work
by Dunne and Krasnansky on Euler-Heisenberg lagrangians in various dimensions,
in the present work we initiate a new line of attack on this problem by
deriving and proving the analogous predictions in the simpler setting of 1+1
dimensional QED. In the first part of this series, we obtain a generalization
of the formula of Affleck et al. to this case, and show that, for both Scalar
and Spinor QED, it correctly predicts the leading asymptotic behaviour of the
weak field expansion coefficients of the two loop Euler-Heisenberg lagrangians.Comment: 28 pages, 1 figures, final published version (minor modifications,
refs. added
Effect of grain disorientation on early fatigue crack propagation in face-centred-cubic polycristals: A three-dimensional dislocation dynamics investigation
Three-dimensional dislocation dynamics simulations are used to study
micro-crack interaction with the first micro-structural barrier in face-centred
cubic bi-crystals loaded in high cycle fatigue conditions. In the examined
configuration, we assumed that micro-crack transmission occurs due to surface
relief growth in the secondary grain ahead of the primary crack. This indirect
transmission mechanism is shown to strongly depend on grain-1/grain-2
disorientation. For instance, small grain disorientation induces plastic strain
localisation ahead of the crack and faster transmission through the first
barrier. Conversely, large grain-1/grain-2 disorientation induces plastic
strain spreading similar to crack tip blunting yielding slower indirect
transmission. A semi-analytical micro-model is developed based on the present
simulation results and complementary experimental observations highlighting the
original notion of first-barrier compliance. The model captures well known
experimental trends including effects of: grain-size, grain disorientation and
micro-crack retardation at the first barrier
Water droplet excess free energy determined by cluster mitosis using guided molecular dynamics
Atmospheric aerosols play a vital role in affecting climate by influencing the properties and lifetimes of clouds and precipitation. Understanding the underlying microscopic mechanisms involved in the nucleation of aerosol droplets from the vapour phase is therefore of great interest. One key thermodynamic quantity in nucleation is the excess free energy of cluster formation relative to that of the saturated vapour. In our current study, the excess free energy is extracted for clusters of pure water modelled with the TIP4P/2005 intermolecular potential using a method based on nonequilibrium molecular dynamics and the Jarzynski relation. The change in free energy associated with the "mitosis" or division of a cluster of N water molecules into two N/2 sub-clusters is evaluated. This methodology is an extension of the disassembly procedure used recently to calculate the excess free energy of argon clusters [H. Y. Tang and I. J. Ford, Phys. Rev. E 91, 023308 (2015)]. Our findings are compared to the corresponding excess free energies obtained from classical nucleation theory (CNT) as well as internally consistent classical theory (ICCT). The values of the excess free energy that we obtain with the mitosis method are consistent with CNT for large cluster sizes but for the smallest clusters, the results tend towards ICCT; for intermediate sized clusters, we obtain values between the ICCT and CNT predictions. Furthermore, the curvature-dependent surface tension which can be obtained by regarding the clusters as spherical droplets of bulk density is found to be a monotonically increasing function of cluster size for the studied range. The data are compared to other values reported in the literature, agreeing qualitatively with some but disagreeing with the values determined by Joswiak et al. [J. Phys. Chem. Lett. 4, 4267 (2013)] using a biased mitosis approach; an assessment of the differences is the main motivation for our current study
Modification of established rejection of canine kidney and liver homografts with antilymphocyte gamma-G globulin
Heterologous ALG was administered to ten canine recipients of renal homografts and one recipient of an orthotopic liver. Treatment was started after rejection was well established. Death from homograft failure was thereby significantly delayed and in several experiments the rejection was at least partially reversed. © 1969
Regional income and employment impacts of farming and forestry in the Mackenzie / Waitaki Basin
This research report documents the likely economic impacts (on regional income and employment) of a change in Mackenzie Basin land use from farming to forestry
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