21,842 research outputs found
Quantifying Shannon's Work Function for Cryptanalytic Attacks
Attacks on cryptographic systems are limited by the available computational
resources. A theoretical understanding of these resource limitations is needed
to evaluate the security of cryptographic primitives and procedures. This study
uses an Attacker versus Environment game formalism based on computability logic
to quantify Shannon's work function and evaluate resource use in cryptanalysis.
A simple cost function is defined which allows to quantify a wide range of
theoretical and real computational resources. With this approach the use of
custom hardware, e.g., FPGA boards, in cryptanalysis can be analyzed. Applied
to real cryptanalytic problems, it raises, for instance, the expectation that
the computer time needed to break some simple 90 bit strong cryptographic
primitives might theoretically be less than two years.Comment: 19 page
Quantifying Resource Use in Computations
It is currently not possible to quantify the resources needed to perform a
computation. As a consequence, it is not possible to reliably evaluate the
hardware resources needed for the application of algorithms or the running of
programs. This is apparent in both computer science, for instance, in
cryptanalysis, and in neuroscience, for instance, comparative neuro-anatomy. A
System versus Environment game formalism is proposed based on Computability
Logic that allows to define a computational work function that describes the
theoretical and physical resources needed to perform any purely algorithmic
computation. Within this formalism, the cost of a computation is defined as the
sum of information storage over the steps of the computation. The size of the
computational device, eg, the action table of a Universal Turing Machine, the
number of transistors in silicon, or the number and complexity of synapses in a
neural net, is explicitly included in the computational cost. The proposed cost
function leads in a natural way to known computational trade-offs and can be
used to estimate the computational capacity of real silicon hardware and neural
nets. The theory is applied to a historical case of 56 bit DES key recovery, as
an example of application to cryptanalysis. Furthermore, the relative
computational capacities of human brain neurons and the C. elegans nervous
system are estimated as an example of application to neural nets.Comment: 26 pages, no figure
Hard x-ray or gamma ray laser by a dense electron beam
A coherent x-ray or gamma ray can be created from a dense electron beam
propagating through an intense laser undulator. It is analyzed by using the
Landau damping theory which suits better than the conventional linear analysis
for the free electron laser, as the electron beam energy spread is high. The
analysis suggests that the currently available physical parameters would enable
the generation of the coherent gamma ray of up to 100 keV. The electron quantum
diffraction suppresses the FEL action, by which the maximum radiation energy to
be generated is limited
Thermodynamics of warped AdS black hole in the brick wall method
The statistical entropy of a scalar field on the warped AdS black hole in
the cosmological topologically massive gravity is calculated based on the
brick-wall method, which is different from the Wald's entropy formula giving
the modified area law due to the higher-derivative corrections in that the
entropy still satisfies the area law. It means that the entropy for scalar
excitations on this background is independent of higher-order derivative terms
or the conventional brick wall method has some limitations to take into account
the higher-derivative terms.Comment: 12 pages, 1 figure; v2. to appear in Phys. Lett. B; v3. typos
correcte
Future singularity free accelerating expansion with the modified Poisson brackets
We show that the second accelerating expansion of the universe appears
smoothly from the decelerating universe remarkably after the initial inflation
in the two-dimensional soluble semi-classical dilaton gravity along with the
modified Poisson brackets of noncommutativity between the relevant fields.
However, the ordinary solution coming from the equations of motion following
the conventional Poisson algebra describes permanent accelerating universe
without any phase change. In this modified model, it turns out that the phase
transition is related to the noncommutative Poisson algebra.Comment: 13 pages, 2 figures; v2. to appear in Phys. Rev.
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