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Fuster-Sabater A.,Institute of Physical and Information Technologies ITEFI
Applied Mathematics and Information Sciences | Year: 2014

In the present work, it is shown that the sequences obtained from cryptographic generators based on decimation are just particular solutions of a kind of linear difference equations. Moreover, all these sequences are simple linear combinations of a class of basic sequences (binomial sequences). Cryptographic parameters of decimated sequences, e.g. period, linear complexity or balancedness, can be analyzed in terms of solutions to linear equations. In brief, difference equations are useful tools for the generation of new cryptographic sequences with application in stream ciphers. Source


Fuster-Sabater A.,Institute of Physical and Information Technologies ITEFI
Procedia Computer Science | Year: 2014

Large Linear Complexity (LC) is a fundamental requirement for a binary sequence to be used in secret key cryptography. In this paper, a method of computing all the nonlinear filtering functions applied to a shift register with a linear complexity LC ≥ (L k) + (L k-1), where L is the register's length and k the order of the filter, is proposed. Emphasis is on the simple algebraic operations (addition and shifting of functions) included in the calculations. The method formally completes the family of nonlinear functions whose filtered sequences satisfy the previous lower bound on LC. In cryptographic terms, it means an easy and useful way of designing sequence generators for cryptographic purposes. © The Authors. Published by Elsevier B.V. Source


Encinas A.H.,University of Salamanca | Gayoso-Martinez V.,Institute of Physical and Information Technologies ITEFI | Martin del Rey A.,University of Salamanca | Martin-Vaquero J.,University of Salamanca | Queiruga-Dios A.,University of Salamanca
International Journal of Modern Physics C | Year: 2016

In this paper, we discuss the problem of solving nonlinear Klein–Gordon equations (KGEs), which are especially useful to model nonlinear phenomena. In order to obtain more exact solutions, we have derived different fourth- and sixth-order, stable explicit and implicit finite difference schemes for some of the best known nonlinear KGEs. These new higher-order methods allow a reduction in the number of nodes, which is necessary to solve multi-dimensional KGEs. Moreover, we describe how higher-order stable algorithms can be constructed in a similar way following the proposed procedures. For the considered equations, the stability and consistency of the proposed schemes are studied under certain smoothness conditions of the solutions. In addition to that, we present experimental results obtained from numerical methods that illustrate the efficiency of the new algorithms, their stability, and their convergence rate. © 2016 World Scientific Publishing Company Source


Fuster-Sabater A.,Institute of Physical and Information Technologies ITEFI
International Journal of Nonlinear Sciences and Numerical Simulation | Year: 2014

In the present work, it is shown that the sequences obtained from a cryptographic sequence generator, the so-called shrinking generator, are just particular solutions of a type of linear difference equations. Moreover, all these sequences are simple linear combinations of m-sequences weighted by other sequences that correspond to the diagonals of the Sierpinski's triangle. These facts suggest a subtle link between irregular decimation and linearity that can be conveniently exploited in the analysis of cryptographic sequences. Previous ideas can be easily extended to other decimation-based cryptographic generators as well as to interleaved sequence generators. © 2014 by Walter de Gruyter Berlin/Munich/Boston. Source


Cobo P.,Institute of Physical and Information Technologies ITEFI | Moraes E.,Federal University of Para | Simon F.,Institute of Physical and Information Technologies ITEFI
Building and Environment | Year: 2015

Absorbing materials are fundamental for the acoustic design of buildings. They are used for increasing the insulation from either outdoor or neighbour noise and for raising the acoustic comfort of dwellings. If environmental and health issues are not of concern, conventional sound absorbers, namely synthetic foams and fibrous materials, offer an excellent acoustical performance at a moderate cost. However, the current trend towards eco-efficient products encourages the enhanced use of natural fibre and loose granular recycled materials. Whatever the material type, a model is required to reliably predict its acoustical performance. The microstructural Champoux-Stinson model has demonstrated to provide consistent acoustical predictions once five non-acoustical parameters are given. Instead of measuring these non-acoustical parameters, which is a rather sophisticated and time consuming procedure, an inverse method, based on Simulated Annealing, is proposed in this paper to estimate them from a single and simple measurement of the absorption coefficient. Experimental results on two samples of loose aquarium gravel validate the proposed inverse method. © 2015 Elsevier Ltd. Source

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