Novel Hybrid Cryptosystem Based on Quasi Group, Chaotic and ElGamal Cryptography

Abstract

In this thesis, a hybrid cryptosystem as proposed, it consists of public and private key cryptosystems; it combines the advantages of these cryptosystem types. Elgamal public key cryptosystem is improved; its disadvantages have been eliminated. In the private key cryptosystem, we investigate the usage of chaotic maps in cryptography, their properties, such as sensitive dependency on initial conditions and system parameters, and random-like outputs, are similar to confusion and diffusion cryptography properties. Furthermore, quasi groups provide a powerful technique for generating a larger set of permutation transformations, so, we adopt the chaotic maps and quasi groups in our proposed cryptosystem. Experimental results are explored in this thesis to demonstrate the efficiency of the proposed cryptosystem. We illustrate the security of the proposed cryptosystem using different data types, we confirm that the proposed cryptosystem is secure against each of the chosen ciphertext attacks, statistics analysis, plaintext attacks, differential attacks and brute force attacks, it destroys the plaintext characteristics. Furthermore, the sensitivity analysis proves the robustness and the high security level of the proposed cryptosystem. Also the scheme is highly secure against the entropy attacks. We construct the private key cryptosystem to deal with a sound signal, it performs good results, and it gives high entropy and destroys the characteristics of the original signal. We develop a novel image cryptosystem by using two color spaces, in order to work in image space components level, which means we change the values of red, green, blue, luminance and color-difference components, for each pixel. This method gives outstanding results; it maximizes the entropy to be very close to the theoretical value, also the results of other measures are very good. It's clear from the measurements results and visual inspection, that the encrypted image contains new colors (which not existed in the original image), besides the new distribution of colors which appears in the encrypted image.