Nowadays, alternative models of elliptic curves like Montgomery, Edwards, twisted Edwards, Hessian, twisted Hessian, Huff’s curves and many others are very popular and many people use them in cryptosystems which are based on elliptic curve cryptography. Most of these models allow to use fast and complete arithmetic which is especially convenient in fast implementations that are side-channel attacks resistant. Montgomery, Edwards and twisted Edwards curves have always order of group of rational points divisible by 4. Huff’s curves have always order of rational points divisible by 8. Moreover, sometimes to get fast and efficient implementations one can choose elliptic curve with even bigger cofactor, for example 16. Of course the bigger cofactor is, the smaller is the security of cryptosystem which uses such elliptic curve. In this article will be checked what influence on the security has form of cofactor of elliptic curve and will be showed that in some situations elliptic curves with cofactor divisible by 2m are vulnerable for combined small subgroups and side-channel attacks.
Defending against DoS (denial of service) attacks has become a great challenge, especially for institutions that provide access to their services in the public network. State-of-the-art identity concealing tools and vast number of computers connected to the network require ensuring appropriate means for entities at risk to enable defence from the particular type of threats. This article presents a concept of user authentication in IP communication. The concept consists in providing the receiver with the possibility to determine sender՚s identity at the Internet layer level. This provides both the capability of defence against DoS attacks and possibility of utilizing the presented model over existing Internet network, which is directly responsible for transmission. The authors hope that the concept is a significant step in the perception of public network data transmission.
This article describes security mechanisms used by 3rd-7th layers in OSI/ISO network model. Many of commonly used protocols by these layers were designed with assumption that there are nointruders. Such assumption was true many years ago. The network situation has been changed for last few years and we should realize that some properties of existing protocols may be abused. Moreover, we should exchange some of them or create new versions. There are some methods and guidelines concerning secure programming, but there is also lack of guidelines about creating secure protocols. Authors see the necessity of such guideline and this article is an attempt at analysing existing solutions and selecting some universal and important patterns.
The Kirchhoff-law-Johnson-noise (KLJN) scheme is a statistical/physical secure key exchange system based on the laws of classical statistical physics to provide unconditional security. We used the LTSPICE industrial cable and circuit simulator to emulate one of the major active (invasive) attacks, the current injection attack, against the ideal and a practical KLJN system, respectively. We show that two security enhancement techniques, namely, the instantaneous voltage/current comparison method, and a simple privacy amplification scheme, independently and effectively eliminate the information leak and successfully preserve the system’s unconditional security.
The paper presents numerical simulations related to the problem of how to obtain correct results in transonic wind tunnel during tests at high airfoil angles of attack. At this flow conditions, significant pressure losses appear in the test section, what leads to significant errors in measured data. Regarding the possible ways of tunnel reconstruction, we examined three different possibilities of changing the test section configurations: an increase of the test section height, displacement of the airfoil below the tunnel centreline and, finally, introduction of divergent test section walls. It was shown that neither the use of higher test section, nor the change of the airfoil location, gives any significant improvement in reference to the existing tunnel configuration. Only after divergent test section walls were introduced, the distributions of pressure coefficient became well consistent with their expected values.
This paper presents a numerical analysis on turbulent flow and forced-convection characteristics of rectangular solar air heater tube fitted with staggered, transverse, V-shape, modern obstacles on the heated walls. Air, whose Prandtl number is 0.71, is the working fluid used, and the Reynolds number considered equal to 6×103. The governing flow equations are solved using a finite volume approach and the semi-implicit pressure linked equation (SIMPLE) algorithm. With regard to the flow characteristics, the quadratic upstream interpolation for convective kinetics differencing scheme (QUICK) was applied, and a second-order upwind scheme (SOU) was used for the pressure terms. The dynamic thermo-energy behavior of the V-shaped baffles with various flow attack angles, i.e., 50°, 60°, 70°, and 80° are simulated, analyzed, and compared with those of the conventional flat rectangular baffles with attack value of 90°. In all situations, the thermal transfer rate was found to be much larger than unity; its maximum value was around 3.143 for the flow attack angle of 90° and y = H/2.
Flow mechanism under roughened solar air heater is quite complex. This paper is an effort towards determining the governing equations for heat transfer and friction factor for inclined spherical balls roughened ducts. With the availability of these equations, it is easier to predict the thermal and thermohydraulic performance of such roughened solar air heaters. The governing equations are derived based on the experimental data generated under actual outdoor condition at the test rig designed and fabricated at the terrace of the Mechanical Engineering Department, the National Institute of Technology Jamshedpur in India, in terms of roughness and flow parameters. Maximum augmentation in Nusselt number and friction factor for varying relative roughness pitch, relative roughness height, spherical ball height to diameter ratio, and angle of attack was respectively found to be of the order of 2.1 to 3.54 times, 1.87 to 3.21 times, 2.89 to 3.27 times and 1.74 to 3.56 times for Nusselt number and 0.84 to 1.79 times, 1.46 to 1.91 times, 1.67 to 2.34 times and 1.21 to 2.67 times for friction factor in comparison to non-roughened duct. The optimum roughness parameters under present investigation have been found.
In Western music culture instruments have been developed according to unique instrument acoustical features based on types of excitation, resonance, and radiation. These include the woodwind, brass, bowed and plucked string, and percussion families of instruments. On the other hand, instrument performance depends on musical training, and music listening depends on perception of instrument output. Since musical signals are easier to understand in the frequency domain than the time domain, much effort has been made to perform spectral analysis and extract salient parameters, such as spectral centroids, in order to create simplified synthesis models for musical instrument sound synthesis. Moreover, perceptual tests have been made to determine the relative importance of various parameters, such as spectral centroid variation, spectral incoherence, and spectral irregularity. It turns out that the importance of particular parameters depends on both their strengths within musical sounds as well as the robustness of their effect on perception. Methods that the author and his colleagues have used to explore timbre perception are: 1) discrimination of parameter reduction or elimination; 2) dissimilarity judgments together with multidimensional scaling; 3) informal listening to sound morphing examples. This paper discusses ramifications of this work for sound synthesis and timbre transposition.