الفهرس 
Introduction to CryptographyOnly 14 pages are availabe for public view
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Abstract
According to the fast progression of digital communication systems, information security becomes indispensable in data exchange and storage.Sharing information and data over unsecured channel is liable for stealing and attacking, as a result cryptography becomes one of the most indispensable issues that provides data authentication. This thesis proposes 1. Modification on the Serpent algorithm for image’s encryption which based on chaotic mapping and cyclic group substitution instead of byte substitution transformation which will decrease the number of rounds and the time usage. A comparison with the classical AES will be declared. The empirical results approved that the modified encryption algorithm provides comparable security and higher performance than the classical Serpent. Elaborated results in terms of implementation, security analysis and statistical tests are declared. Comparative study with classical Serpent encryption algorithms is shown the notability of our modification. 2. Technique of digital signature scheme which combines elliptic curve crypto system (ECC) with Ong, Schnorr and Shamir signature scheme (OSS). A self-in vertible 4×4 key matrix will be used as apart from OSS signature equations which will increase the overall security and efficiency against crypt analytic attack. Elaborated results in terms of implementation and security analysis are declared and approved its strength. The proposed technique can be used as a secure alternative protocol if known systems are broken. As an application, the proposed algorithm has been applied on smart cards and simulated using Lab View program. 3. Concept for image encryption using a new method based on the Meaning of Location (MOL) and the Output Feedback Mode (OFB). In this method, the public key is an image which will be converted into RGB numbers and the private key is random integers used to permutate the image. The initialization vector of the “OFB” mode is going to be encrypted using the locations of the RGB numbers. Security analysis of the proposed algorithm has been measured and approved its strength. Statistical tests show that the MOL-OFB algorithm is suitable for securing multimedia applications and it has the potential to secure communication systems in a variety of wired/wireless scenarios such as mobile phone services and smart cards. A series of calculations was conducted using the new developed algorithm as applied to different types of data (e.g. text, graphics and geographic maps). In all research experiment, the encrypted and decrypted files were exactly the same. The work reported in this thesis may find its applications in either military or civilian communications.