Galal Elkobrosy

Certificate-based authenticated key agreement protocols

In this paper, the problem of establishing a shared session key in an authenticated way is addressed. New key agreement protocols that support explicit authentication are proposed. The protocols are designed in such a way that permits a trusted third party, such as a firewall, to verify the identities of the parties involved in a key agreement session. This is of course to reduce the computational burden at the end-user side, which can be a device with limited capabilities. The security properties of the proposed protocols are analyzed revealing the strength of these protocols promoting their use in practical scenarios such as in mobile communications.

Extension and application of El-Gamal encryption scheme

Security is an essential requirement in the industrial world. Information leakage to competitors can cause financial problems for a company. Moreover, the wide use of the Internet as an environment for doing business and shopping calls for secure electronic transactions. Confidentiality of the information is preserved through the use of encryption schemes. This paper proposes a new three-party extension of ElGamal encryption scheme and a multi-receiver extension of ElGamal encryption scheme. For both of the two proposed schemes, security and performance are analyzed. Finally, the application of El-Gamal encryption scheme in internet voting is studied for its importance nowadays.

Cartesian Parallel Manipulator Modeling, Control and Simulation

Parallel manipulators are robotic devices that differ from the more traditional serial robotic manipulators by their kinematic structure. Parallel manipulators are composed of multiple closed kinematic loops. Typically, these kinematic loops are formed by two or more kinematic chains that connect a moving platform to a base, where one joint in the chain is actuated and the other joints are passive. This kinematic structure allows parallel manipulators to be driven by actuators positioned on or near the base of the manipulator. In contrast, serial manipulators do not have closed kinematic loops and are usually actuated at each joint along the serial linkage. Accordingly, the actuators that are located at each joint along the serial linkage can account for a significant portion of the loading experienced by the manipulator, whereas the links of a parallel manipulator generally need not carry the load of the actuators. This allows the parallel manipulator links to be made lighter than the links of an analogous serial manipulator. The most noticeable interesting features of parallel mechanisms being: • High payload capacity. • High throughput movements (high accelerations). • High mechanical rigidity. • Low moving mass. • Simple mechanical construction. • Actuators can be located on the base. However, the most noticeable disadvantages being: • They have smaller workspaces than serial manipulators of similar size. • Singularities within working volume. • High coupling between the moving kinematic chains.

Observation and simulation of a large signal mechanical vibrating system

The equation of motion of n-degrees of freedom non-conservative mechanical system is represented by a Vector-Matrix differential equation. The matrix method is usually used where the natural frequencies and natural modes of vibrations are obtained, to solve this equation and a similarity transformation is always required to obtain the steady state solution. The purpose of this paper is to propose a solution, based on Cayley-Hamilton theorem, to the equation of motion of n-degrees of freedom discrete non-conservative mechanical system. The similarity transformation is not required in the proposed method, and contrary to the classical matrix method, the computations to be carried out are moderate, thus enabling use of personal computers. Simulated examples are presented to illustrate the results given in this paper.

Two-Phase Image Encryption Scheme Based on FFCT and Fractals

This paper blends the ideas from recent researches into a simple, yet efficient image encryption scheme for colored images. It is based on the finite field cosine transform (FFCT) and symmetric-key cryptography. The FFCT is used to scramble the image yielding an image with a uniform histogram. The FFCT has been chosen as it works with integers modulo and hence avoids numerical inaccuracies inherent to other transforms. Fractals are used as a source of randomness to generate a one-time-pad keystream to be employed in enciphering step. The fractal images are scanned in zigzag manner to ensure decorrelation of adjacent pixels values in order to guarantee a strong key. The performance of the proposed algorithm is evaluated using standard statistical analysis techniques. Moreover, sensitivity analysis techniques such as resistance to differential attacks measures, mean square error, and one bit change in system key have been investigated. Furthermore, security of the proposed scheme against classical cryptographic attacks has been analyzed. The obtained results show great potential of the proposed scheme and competitiveness with other schemes in literature. Additionally, the algorithm lends itself to parallel processing adding to its computational efficiency.

On Input Signal Synthesis for Parameter Estimation with Output Power Constraints

Abstract The paper considers the problem of input signal design for estimating parameters in stochastic dynamical systems. We consider the case where the variance of the system output can not be greater than some prescribed value. The input signals are optimal in the sense of maximizing a scalar function of the system information matrix. A new algorithm is described in which the input signal is calculated in real time based on the current parameter estimates of the unknown parameters. The computations to be carried out at each sampling interval are moderate and the algorithm is well suited for on-line identification methods. Further, the algorithm will be modified for systems operating in closed-loop. Two examples are presented to illustrate the properties of the algorithm.

Accuracy Aspects of Parameter Estimation in Linear Dynamical Systems

Abstract The paper considers the influence of feedback on the accuracy of parameter estimates in discrete-time stochastic dynamical systems. It was shown by Goodwin and Payne (1977), and others, that the accuracy of noise parameters is independent of the input signal used for a certain classes of systems. This result has been considered in the design of optimal input signal by some authors, e.g. Zarrop (1979). However, it will be shown that for a commonly used model, Astrom model, in system identification and adaptive control, the accuracy of noise parameters are dependent of experimental conditions. The relation between the accuracies of system and noise parameter estimates will be derived. Results concerning the role of feedback in identification experiment will be presented and illustrated by examples.

On the modeling and control of the Cartesian Parallel Manipulator

The Cartesian Parallel Manipulator (CPM) which proposed by Han Sung Kim, and Lung-Wen Tsai [1] consists of a moving platform that is connected to a fixed base by three limbs. Each limb is made up of one prismatic and three revolute joints and all joint axes are parallel to one another. In this way, each limb provides two rotational constraints to the moving platform and the combined effects of the three limbs lead to an over-constrained mechanism with three translational degrees of freedom. The manipulator behaves like a conventional X-Y-Z Cartesian machine due to the orthogonal arrangement of the three limbs.

A comprehensive study of the non-linear euler-bernoulli rotating beam

Abstract The main goal of this work is to analyze the behavior of Euler-Bernoulli rotating beam with constant angular velocity around Z-axis. Our dynamic model is analyzed considering only the in-plane transverse deformation. Thus the model is defined by an ordinary differential equation with one degree of freedom (O.D.F) and the governing differential equation is Duffings equation with a variable coefficient for the linear term. When the damping coefficient and the amplitude of the excitation force are zeros, the system is autonomous with an explicitly known homoclinic orbit. The homoclinic orbits is calculated. Melnikov function due to the homoclinic orbit is calculated to detect the transverse homoclinic orbit. Also a dynamic numerical simulation methods are used to obtain the time history, phase portrait, Laypunov exponent, power spectrum, Poincare’ maps and their fractal dimensions. A comparison has been done between this O.D.F. model and the 2nd D.F. model that we have analyzed in [23]. The numerical results showed the occurrence of regular motion and chaotic motion in both models. Thus, by reducing the order of the two-coupled Duffings equations into an ordinary differential equation with O.D.F. a more simplified model for the flexible rotating beam is achieved.