A Practical Attack on the MIFARE Classic

The MIFARE Classic is the most widely used contactless smart card in the market. Its design and implementation details are kept secret by its manufacturer. This paper studies the architecture of the card and the communication protocol between card and reader. Then it gives a practical, low-cost, attack that recovers secret information from the memory of the card. Due to a weakness in the pseudo-random generator, we are able to recover the keystream generated by the CRYPTO1 stream cipher. We exploit the malleability of the stream cipher to read all memory blocks of the first sector of the card. Moreover, we are able to read any sector of the memory of the card, provided that we know one memory block within this sector. Finally, and perhaps more damaging, the same holds for modifying memory blocks

Efficient Computer Simulation of Polymer Conformation. I. Geometric Properties of the Hard-Sphere Model

A system of efficient computer programs has been developed for simulating the conformations of macromolecules. The conformation of an individual polymer is defined as a point in conformation space, whose mutually orthogonal axes represent the successive dihedral angles of the backbone chain. The statistical-mechanical average of any property is obtained as the usual configuration integral over this space. A Monte Carlo method for estimating averages is used because of the impossibility of direct numerical integration. Monte Carlo corresponds to the execution of a Markoffian random walk of a representative point through the conformation space. Unlike many previous Monte Carlo studies of polymers, which sample conformation space indiscriminately, importance sampling increases efficiency because selection of new polymers is biased to reflect their Boltzmann probabilities in the canonical ensemble, leading to reduction of sampling variance and hence to greater accuracy! in given computing time. The simulation is illustrated in detail. Overall running time is proportional to n^(5/4), where n is the chain length. Results are presented for a hard-sphere linear polymer of n atoms, with free dihedral rotation, with n = 20-298. The fraction of polymers accepted in the importance sampling scheme, fA, is fit to a Fisher-Sykes attrition relation, giving an effective attrition constant of zero. fA is itself an upper bound to the partition function, Q, relative to the unrestricted walk. The mean-squared end-to-end distance and radius of gyration exhibit the expected exponential dependence, but with exponent for the radius of gyration significantly greater than that of the end-to-end distance. The 90% confidence limits calculated for both exponents did not include either 6/5 or 4/3, the lattice and zero-order perturbation values, respectively. A self-correcting scheme for generating coordinates free of roundoff error is given in an Appendix

Structural optimization incorporating centrifugal and Coriolis effects

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76768/1/AIAA-1989-1310-955.pd

Computer Simulation of Polymer Conformation. II. Distribution Function for Polymers with Excluded Volume

Numerical distributions of end-to-end distances were generated by a Monte Carlo method for hard-sphere off-lattice polymers of length N = 20, 40, 60, 80, 98, and 298 atoms. Comparison by xz tests against five recently proposed theoretical distribution functions showed that for N = 80 and N = 98, the data could be described, with 95% confidence, by the equation f(r) = exp[ -(ar2 + br + c)], where a and b are fitted parameters and c is a normalization constant. For N = 298, limitations of sample size lead to lower confidence limits (about 80%), but good fit. The above equation, and not its gaussian counterpart exp( -cr^2), is probably the limiting distribution function. The function accurately predicts the 1st through 12th observed moments at all chain lengths

Estimation of electrical resistivity of conductive materials of random shapes

Introduction. Electrical resistivity is an important material characteristic in the field of electrical engineering and material science. There are several methods that can be used to measure resistance, like the 4-wire method which relates the resistance to a voltage drop at a given current flow, but to define the resistivity from the resistance value requires an analytical expression for the given system which requires a sufficient mathematical apparatus for describing complicated shapes. Therefore we use finite element method computations to compute the resistivity of a metal material. This approach has been already used for different materials like concrete and aluminum in the past. We then compare this method with an analytical expression that due to intuition could approximate the solution sufficiently. After that, the same material is used again to test the electrical isotropy of the sample. Novelty. A method is developed by combining the results of experimental studies and the results of mathematical modelling of the process of determining the electrical conductivity of metals. The goal is to describe and employ a method of measuring the electrical resistivity of metal objects of random shapes. Using this method, it is possible to measure the resistivity of materials without the need to manufacture them into wires or ribbons. Methods. The solution to the problem was carried out by the finite element method via the COMSOL Multiphysics 5.6 simulation program in a cartesian coordinate system and the resistance between two points of the metal sample was measured by the 4-wire method. Results. A similar resistance value was obtained when the measuring terminals were placed in different places. The difference between them was within 1,5 % and the obtained values were close to the values given by the literature for the electrical resistivity of electrical steels. Terminal size influences the measured conductivity and a max error of 5,2 % was estimated. Practical value. A method of estimating the resistivity of materials without the need to manufacture them into specific shapes, like wires or ribbons, for which analytical expressions between resistivity and resistance are easily derived.Вступ. Питомий електричний опір є важливою характеристикою матеріалу в галузі електротехніки та матеріалознавства. Існує кілька методів, які можна використовувати для вимірювання опору, наприклад, 4-провідний метод, який пов’язує опір з падінням напруги при заданому струмі, але для визначення питомого опору за значенням опору потрібен аналітичний вираз для даної системи, який вимагає достатнього математичного апарату для опису складних форм. Тому ми використовуємо розрахунки методом скінченних елементів до розрахунку питомого опору металевого матеріалу. Цей підхід вже використовувався в минулому для різних матеріалів, таких як бетон та алюміній. Потім ми порівнюємо цей метод з аналітичним виразом, який завдяки інтуїції може достатньо апроксимувати рішення. Після цього матеріал знову використовується для перевірки електричної ізотропії зразка. Новизна. Розроблено метод шляхом поєднання результатів експериментальних досліджень та результатів математичного моделювання процесу визначення електропровідності металів. Мета – описати та застосувати метод вимірювання питомого електичного опору металевих предметів довільної форми. Використовуючи цей метод, можна вимірювати питомий опір матеріалів без необхідності виготовлення дротів або стрічок. Методи. Розв’язання задачі здійснювалося методом скінченних елементів за допомогою програми моделювання COMSOL Multiphysics 5.6 у декартової системі координат, а опір між двома точками металевого зразка вимірювався 4-провідним методом. Результати. Отримано аналогічне значення опору під час розміщення вимірювальних клем у різних місцях. Різниця між ними знаходилася в межах 1,5% і отримані значення були близькими до наведених у літературі значень електричного опору електротехнічних сталей. Розмір клеми впливає на провідність, що вимірюється, максимальна похибка становить 5,2 %. Практична цінність. Метод оцінки питомого опору матеріалів без необхідності надання їм певної форми, наприклад, дроту або стрічок, для якого легко отримати аналітичні вирази між питомим опором та опором

Access regulation and the transition from copper to fiber networks in telecoms

In this paper we study the impact of different forms of access obligations on firms' incentives to migrate from the legacy copper network to ultra-fast broadband infrastructures. We analyze three different kinds of regulatory interventions: geographical regulation of access to copper networks-where access prices are differentiated depending on whether or not an alternative fiber network has been deployed; access obligations on fiber networks and its interplay with wholesale copper prices; and, finally, a mandatory switch-off of the legacy copper network-to foster the transition to the higher quality fiber networks. Trading-off the different static and dynamic goals, the paper provides guidelines and suggestions for policy makers' decision

Efficient Computation of Polymer Conformation Energy

Calculation of intramolecular energy of a polymer due to interactions of non-bonded atoms can be speeded up using simple geometric inequalities. This "zippering" method reduces time dependence of computation from n^2 to n^1.25, where n is the chain length. This technique is especially useful in applications of the pivot algorithm

Nanosecond optical imaging spectroscopy of an electrothermal radiofrequency plasma thruster plume

Nanosecond optical imaging spectroscopy is employed to investigate the spatio-temporal dynamics of the plasma plume expanding from a 4.2 mm-diameter, 20 mm-long cylindrical capacitively coupled electrothermal radiofrequency (rf) driven thruster using 10 W of power at 12.50 MHz and an argon pressure of 1.5 Torr. On-axis, the plume exhibits four distinct peaks of optical emission intensity within the rf period. The plume has a spherical shape with a transient radial extension (during half of the rf cycle) at the thruster exit plane due to an rf current to ground when the grounded electrode acts as an anode

Formation of spatially periodic fronts of high-energy electrons in a radio-frequency driven surface microdischarge

The generation of spatially periodic fronts of high-energy electrons (>13.48 eV) has been investigated in a radio-frequency surface microdischarge in atmospheric-pressure argon. Optical emission spectroscopy is used to study the Ar I 2p1−1s2 transition surrounding a filamentary microdischarge, both spatially and with respect to the phase of the applied voltage. The formation of excitation fronts, which remain at a constant propagation distance throughout the RF cycle and for the duration of the pulse, may be explained by a localized increase in the electric field at the tip of surface-charge layers that are deposited during the extension phase