الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
In today’s world of multiple and diverse communication means, information security is a major issue. Cryptography, which is the science that deals with information security, is an active science, that is in continues study and development. A vital building block in cryptography is the block cipher. In block cipher, a block with a certain length is encrypted at a time using the secret key. Block cipher is classified into two major ciphers according to secret key type; these are; symmetric (private) key cipher, and asymmetric (public) key cipher. Symmetric key ciphers use the same key into encryption and decryption process, so that the secret key should be transferred between users in secure channels. In the other hand asymmetric key ciphers use two different keys in each process, a public key, which is used in encryption process - distributed over a public channel- and a private key, which is used into decryption process - known and chosen by the user-. This thesis concentrates on symmetric key ciphers.
There are two types of ciphering processes; these are; substitution and permutation. Any cipher consists of successive stages of substitutions and permutations. Cryptosystems can be divided into two types depending on the block length; those are mono-alphabetic ciphers, and poly-alphabetic ciphers. The most modem cryptosystems are considered as ploy-alphabetic ciphers. The most popular classical ciphers are; CAESAR cipher, substitution cipher, PLAYFAIR cipher, HILL cipher, AFFINE cipher, VIGENERE cipher, and permutation cipher. The structure and performance of each above ciphers are descried in details in the thesis. The most popular modern cryptosystems structure and performance are described in details in the thesis too. These modern cryptosystems are DBS, GOST, BLOWFISH, IDEA, RC5, and RIJNDAEL. MANKAREA is a new proposed cryptosystem, built on the principle of multiple stage cryptosystems or multi-tire cryptosystem to gain the security advantages of each cryptosystems used into each stage. Each stage in MANKAREA will overcome any shortcuts - if there were any -of the other stages, and will hide the statistics of the other stages. MANKAREA detailed structure, performance, and statistics is described in details inside the thesis.