الفهرس 
Design of Link Encryption Algorithm : LEAOnly 14 pages are availabe for public view
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Abstract
Research and development in network security have mainly followed two lines. One line studies cryptography and uses it to devise security services. The other line examines loopholes and side effects of existing network protocols, software, and system configurations. Our goal in this thesis is intended to provide a balanced treatment of network security along the first line, with adequate materials and sufficient depth for explaining a network security. Network encryption is a network security process that applies crypto services at the network transfer layer. Using the existing network services and application software, network encryption is invisible to the end user and operates independently of any other encryption processes used.
The essential condition for a cryptosystem is that it is intractable to recover the plaintext from the ciphertext without knowing the decryption method and key. Stream ciphers, block ciphers, and hash functions play major roles in providing security services like confidentiality, integrity, authentication, and non repudiation of the data sent through network communication. In this work, three custom encryption algorithms with evaluation performance and security analysis are introduced and combined to produce a proposed cryptosystem as an end to end encryption model, or even used individually for certain cryptographic aspect. This thesis is coming as a solution to secret key agreement problem, with the aid of symmetric key cryptography and without using public key cryptography. The goal is to forward new, secured, and practical approaches to secret key agreement, Key Encryption Algorithm (KEA), which is illustrated to immune attacks based on advances in number theory.
During this work a new encryption scheme using stream cipher algorithm, Link Encryption Algorithm (LEA), is developed to achieve the required confidentiality to the transmitted data. Since the maximal-length linear feedback shift register (LFSR) sequences are considered to be the corner stone of any stream cipher, then the combination of these sequences must be combined with nonlinear function for achieving confusion and diffusion principles of the proposed algorithm. The performance evaluation of the scheme was measured through a series of randomness tests and security analysis. Experimental results demonstrate the proposed system is highly key sensitive, and highly resistant to the well-known attacks. Under this work, the addition of hash function layer to the cryptosystem will enhance the secrecy of the system as well as its implementation type of keyed hash function, Concrete Hash Algorithm (CHA), to the plaintext can be used as message authentication code, digital signature, and data integrity for cryptosystems.
The well known types of cryptanalysis for three proposed encryption algorithms which build a cryptosystem model are reviewed. The cryptanalysis approach is normally determined according to the cryptosystem itself. This fact comes from the almost universal assumption of cryptography by which the cryptanalyst must know the cryptosystem. Using the high level programming, Visual C, the performance of any finite generated sequence can be determined and compared with known public algorithms. Finally, the proposed cryptosystem in this thesis is demonstrated. To demonstrate the encryption functions used by the proposed encryption algorithm, a complete detail for each encryption function and the results of its evaluation are given.