Using classifiers to predict linear feedback shift registers

Proceeding of: IEEE 35th International Carnahan Conference on Security Technology. October 16-19, 2001, LondonPreviously (J.C. Hernandez et al., 2000), some new ideas that justify the use of artificial intelligence techniques in cryptanalysis are presented. The main objective of that paper was to show that the theoretical next bit prediction problem can be transformed into a classification problem, and this classification problem could be solved with the aid of some AI algorithms. In particular, they showed how a well-known classifier called c4.5 could predict the next bit generated by a linear feedback shift register (LFSR, a widely used model of pseudorandom number generator) very efficiently and, most importantly, without any previous knowledge over the model used. The authors look for other classifiers, apart from c4.5, that could be useful in the prediction of LFSRs. We conclude that the selection of c4.5 by Hernandez et al. was adequate, because it shows the best accuracy of all the classifiers tested. However, we have found other classifiers that produce interesting results, and we suggest that these algorithms must be taken into account in the future when trying to predict more complex LFSR-based models. Finally, we show some other properties that make the c4.5 algorithm the best choice for this particular cryptanalytic problem.Publicad

The Influence of Dual-Recycling on Parametric Instabilities at Advanced LIGO

Laser interferometers with high circulating power and suspended optics, such as the LIGO gravitational wave detectors, experience an optomechanical coupling effect known as a parametric instability: the runaway excitation of a mechanical resonance in a mirror driven by the optical field. This can saturate the interferometer sensing and control systems and limit the observation time of the detector. Current mitigation techniques at the LIGO sites are successfully suppressing all observed parametric instabilities, and focus on the behaviour of the instabilities in the Fabry-Perot arm cavities of the interferometer, where the instabilities are first generated. In this paper we model the full dual-recycled Advanced LIGO design with inherent imperfections. We find that the addition of the power- and signal-recycling cavities shapes the interferometer response to mechanical modes, resulting in up to four times as many peaks. Changes to the accumulated phase or Gouy phase in the signal-recycling cavity have a significant impact on the parametric gain, and therefore which modes require suppression.Comment: 9 pages, 11 figures, 2 ancillary file

Identificación y descripción de procesos reales en la universidad EAFIT bajo la perspectiva de sistemas dinámicos

Este trabajo está enfocado hacia el estudio de los sistemas dinámicos en la universidad EAFIT, a partir de visitas realizadas a los laboratorios de la universidad, haciendo una breve descripción de máquinas y procesos bajo la teoría de los sistemas dinámicos, teniendo en cuenta las características más importantes de un sistema dinámico como lo son: entrada, salidas, posibles perturbaciones. Dejando así un importante apoyo para quienes después se puedan interesar tanto en describir como llegar a un posible control de algunos de los procesos, dada la necesidad en la universidad por personas interesadas en este tipo de estudios, pues en las visitas realizadas a dichos laboratorios se pudo observar la falta de interés tanto de los estudiantes como de la misma universidad para realizar un mejor estudio de los procesos, viendo así como muchos de los procesos no son desarrollados de la mejor manera. Hecha la descripción de los procesos, se procederá a un estudio mucho más detallado de dos de estos procesos reales empezando con la modelación y simulación del mismo, bajo la teoría de los sistemas lineales usando como herramienta de simulación MATLAB SIMULINK

La distancia que separa las concepciones didácticas de lo que se hace en clase : el caso de los trabajos de laboratorio en biología

En este artículo se analizan las concepciones sobre los trabajos de laboratorio en biología de un grupo de alumnos de 4º año de la escuela secundaria. A través de un cuestionario verbal abierto y una tarea de selección de tarjetas, se indagó qué tipo de trabajos experimentales los alumnos llevan a cabo en sus clases, qué se aprende de ellos y qué posibilidades encuentran en otras modalidades de trabajos experimentales propuestas por los especialistas en didáctica. Los resultados señalan una brecha entre lo que los alumnos refieren que se realiza en sus clases y las propuestas de los especialistas. En la escuela, predominan las tareas escasamente reflexivas (actividades de carácter descriptivo para verificar e ilustrar temas estudiados), que no ayudan a desarrollar habilidades vinculadas con la investigación, ya que exigen seguir una serie de pasos estipulados en vez de alentar el planteamiento de problemas, la formulación de hipótesis, la búsqueda de respuestas y la interpretación de lo observado.Sixteen-year-old students' ideas about Biological laboratory work done in their classes are revealed through an open questionnaire. They were also validated through a selection task in which students were presented four different instructional situations involving practical work and had to decide which was more frequent in their classes, what can be learned through them, and their personal preferences about the way they would like to be taught. The results show a wide gap between what students say they do in their classes and what experts in the field say that should be done. In schools they are taught through non reflective tasks (with only descriptive demands), which rarely help them develop inquiry skills. They are expected to follow the instructions of their teachers instead of posing problems, thinking of hypotheses, trying to find answers and analyzing what they observe

NMR quantum simulation of localization effects induced by decoherence

The loss of coherence in quantum mechanical superposition states limits the time for which quantum information remains useful. Similarly, it limits the distance over which quantum information can be transmitted, resembling Anderson localization, where disorder causes quantum mechanical states to become localized. Here, we investigate in a nuclear spin-based quantum simulator, the localization of the size of spin clusters that are generated by a Hamiltonian driving the transmission of information, while a variable-strength perturbation counteracts the spreading. We find that the system reaches a dynamic equilibrium size, which decreases with the square of the perturbation strength.Comment: 5 pages, 5 figure

Correlation between magnetic interactions and domain structure in A1 FePt ferromagnetic thin films

We have investigated the relationship between the domain structure and the magnetic interactions in a series of FePt ferromagnetic thin films of varying thickness. As-made films grow in the magnetically soft and chemically disordered A1 phase that may have two distinct domain structures. Above a critical thickness $d_{cr}\sim 30$ nm the presence of an out of plane anisotropy induces the formation of stripes, while for $d<d_{cr}$ planar domains occur. Magnetic interactions have been characterized using the well known DCD-IRM remanence protocols, $\delta M$ plots, and magnetic viscosity measurements. We have observed a strong correlation between the domain configuration and the sign of the magnetic interactions. Planar domains are associated with positive exchange-like interactions, while stripe domains have a strong negative dipolar-like contribution. In this last case we have found a close correlation between the interaction parameter and the surface dipolar energy of the stripe domain structure. Using time dependent magnetic viscosity measurements, we have also estimated an average activation volume for magnetic reversal, $\langle V_{ac}\rangle \sim 1.37\times 10^{4}$ nm$^{3},$ which is approximately independent of the film thickness or the stripe period.Comment: 25 pages, 11 figure