206,359 research outputs found
Enhanced secure key exchange systems based on the Johnson-noise scheme
We introduce seven new versions of the Kirchhoff-Law-Johnson-(like)-Noise
(KLJN) classical physical secure key exchange scheme and a new transient
protocol for practically-perfect security. While these practical improvements
offer progressively enhanced security and/or speed for the non-ideal
conditions, the fundamental physical laws providing the security remain the
same.
In the "intelligent" KLJN (iKLJN) scheme, Alice and Bob utilize the fact that
they exactly know not only their own resistor value but also the stochastic
time function of their own noise, which they generate before feeding it into
the loop.
In the "multiple" KLJN (MKLJN) system, Alice and Bob have publicly known
identical sets of different resistors with a proper, publicly known truth table
about the bit-interpretation of their combination. In the "keyed" KLJN (KKLJN)
system, by using secure communication with a formerly shared key, Alice and Bob
share a proper time-dependent truth table for the bit-interpretation of the
resistor situation for each secure bit exchange step during generating the next
key.
The remaining four KLJN schemes are the combinations of the above protocols
to synergically enhance the security properties. These are: the
"intelligent-multiple" (iMKLJN), the "intelligent-keyed" (iKKLJN), the
"keyed-multiple" (KMKLJN) and the "intelligent-keyed-multiple" (iKMKLJN) KLJN
key exchange systems.
Finally, we introduce a new transient-protocol offering practically-perfect
security without privacy amplification, which is not needed at practical
applications but it is shown for the sake of ongoing discussions.Comment: This version is accepted for publicatio
Bounds on the size of codes
In this dissertation we determine new bounds and properties of codes in
three different finite metric spaces, namely the ordered Hamming space, the
binary Hamming space, and the Johnson space.
The ordered Hamming space is a generalization of the Hamming space that
arises in several different problems of coding theory and numerical
integration. Structural properties of this space are well described in the
framework of Delsarte's theory of association schemes. Relying on this
theory, we perform a detailed study of polynomials related to the ordered
Hamming space and derive new asymptotic bounds on the size of codes in this
space which improve upon the estimates known earlier.
A related project concerns linear codes in the ordered Hamming space. We
define and analyze a class of near-optimal codes, called near-Maximum
Distance Separable codes. We determine the weight distribution and provide
constructions of such codes. Codes in the ordered Hamming space are dual to
a certain type of point distributions in the unit cube used in numerical
integration. We show that near-Maximum Distance Separable codes are
equivalently represented as certain near-optimal point distributions.
In the third part of our study we derive a new upper bound on the size of
a family of subsets of a finite set with restricted pairwise intersections,
which improves upon the well-known Frankl-Wilson upper bound. The new bound
is obtained by analyzing a refinement of the association scheme of the
Hamming space (the Terwilliger algebra) and intertwining functions of the
symmetric group.
Finally, in the fourth set of problems we determine new estimates on the
size of codes in the Johnson space. We also suggest a new approach to the
derivation of the well-known Johnson bound for codes in this space. Our
estimates are often valid in the region where the Johnson bound is vacuous.
We show that these methods are also applicable to the case of multiple
packings in the Hamming space (list-decodable codes). In this context we
recover the best known estimate on the size of list-decodable codes in
a new way
An optimal synchronous bandwidth allocation scheme for guaranteeing synchronous message deadlines with the timed-token MAC protocol
This paper investigates the inherent timing properties of the timed-token medium access control (MAC) protocol necessary to guarantee synchronous message deadlines in a timed token ring network such as, fiber distributed data interface (FDDI), where the timed-token MAC protocol is employed. As a result, an exact upper bound, tighter than previously published, on the elapse time between any number of successive token arrivals at a particular node has been derived. Based on the exact protocol timing property, an optimal synchronous bandwidth allocation (SBA) scheme named enhanced MCA (EMCA) for guaranteeing synchronous messages with deadlines equal to periods in length is proposed. Thm scheme is an enhancement on the previously publiibed MCA scheme
FEM-BEM coupling methods for Tokamak plasma axisymmetric free-boundary equilibrium computations in unbounded domains
International audienceIncorporating boundary conditions at infinity into simulations on bounded computational domains is a repeatedly occurring problem in scientific computing. The combination of finite element methods (FEM) and boundary element methods (BEM) is the obvious instrument, and we adapt here for the first time the two standard FEM-BEM coupling approaches to the free-boundary equilibrium problem: the Johnson-Nédélec coupling and the Bielak-MacCamy coupling. We recall also the classical approach for fusion applications, dubbed according to its first appearance von-Hagenow-Lackner coupling and present the less used alternative introduced by Albanese, Blum and de Barbieri in [2]. We show that the von-Hagenow-Lackner coupling suffers from undesirable non-optimal convergence properties, that suggest that other coupling schemes, in particular Johnson-Nédélec or Albanese-Blum-de Barbieri are more appropriate for non-linear equilibrium problems. Moreover, we show that any of such coupling methods requires Newton-like iteration schemes for solving the corresponding non-linear discrete algebraic systems
FEM-BEM coupling methods for Tokamak plasma axisymmetric free-boundary equilibrium computations in unbounded domains
International audienceIncorporating boundary conditions at infinity into simulations on bounded computational domains is a repeatedly occurring problem in scientific computing. The combination of finite element methods (FEM) and boundary element methods (BEM) is the obvious instrument, and we adapt here for the first time the two standard FEM-BEM coupling approaches to the free-boundary equilibrium problem: the Johnson-Nédélec coupling and the Bielak-MacCamy coupling. We recall also the classical approach for fusion applications, dubbed according to its first appearance von-Hagenow-Lackner coupling and present the less used alternative introduced by Albanese, Blum and de Barbieri in [2]. We show that the von-Hagenow-Lackner coupling suffers from undesirable non-optimal convergence properties, that suggest that other coupling schemes, in particular Johnson-Nédélec or Albanese-Blum-de Barbieri are more appropriate for non-linear equilibrium problems. Moreover, we show that any of such coupling methods requires Newton-like iteration schemes for solving the corresponding non-linear discrete algebraic systems
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