Cryptography and Network Security: Techniques and Algorithms

Salah Mohammad A. E. Kholaif


The essential condition for a cryptosystem to be good is that it is intractable to recover the plaintext, pt, from the ciphertext, ct, without knowing the decryption method Dk and key k. 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, secure, and practical approaches to secret key agreement, Key Encryption Algorithm (KEA), which is illustrated to be immune against attacks based on advances in number theory. During this work a novel 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, thus the combination of these sequences is combined with nonlinear function for building blocks of 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 resistive to the well-known attacks. Under this work, the addition of keyed hash function, CHA, security layer to the proposed secure cryptosystem enhance its secrecy by verifying the integrity security service. It can also be used as message authentication, digital signature, or as a seed to generate random events. Chapter 7 Conclusion an Future Works - --------------------------------------------------------------------------------------- 93 --------------------------------------------------------------------------------------- The well known types of cryptanalysis against the three proposed encryption algorithms which build a cryptosystem model are reviewed. 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. The performance of the software implementation for the three new algorithms, using the high level programming (Visual C), is evaluated and compared with known published algorithms. Finally, the proposed cryptosystem in this thesis is demonstrated. The proposed encryption algorithm as a whole is described by means of the block diagram, the system keys, its main functions, security analysis, and its evaluation results. 7.1 Research Conclusions The work includes an elaborate design of proposed cryptosystem composed of three different symmetric algorithms covering major dimensions of security services, namely confidentiality, integrity, authentication, and non repudiation, which are necessary for conveying information securely through the network. After reviewing probable risks arising from standard algorithm, according to Snowden document [88], and future probable risks of using asymmetric key encryption during rapid developments in GPU and Quantum computers, proposed symmetric cryptosystem were conducted to avoid risks of asymmetric algorithms. Proposed cryptosystem were conducted to establish the merits of three new algorithms. This work contributes to enhance network security system. Also, any individual algorithm from three new algorithms combined in the cryptosystem can be used independently in certain cryptographic application according to the need. 7.2 Future Work Following are the few suggestions for future work: 1. The stream cipher algorithm, LEA can be made available in several different key lengths, by modifying the word size of the LFSR stage. Another innovation is possible by accommodating a compression function to the input message. These improvements will help to customize the security requirements. Chapter 7 Conclusion an Future Works - --------------------------------------------------------------------------------------- 94 --------------------------------------------------------------------------------------- 2. The block cipher algorithm, KEA can be made available in several different block and key length, by varying the number of rounds. Another innovation is possible by increasing number of working users and size of stored and exchanged keys. These improvements are depending on the required cryptographic applications and security requirements. 3. The Hash function, CAH-160 can be made extendable in different lengths, by changing the working word size. Another innovation in security strengths is possible by increasing the number of variables of non-linear Boolean functions. These changes will add strength to resist future unknown attacks. 4. The fourth main security service called non-repudiation blocks the sender's denial that the sender had not sent a particular message. Non repudiation with keyed hash function, CHA-160, technology can be developed to use new randomly generated key each session. This area may be explored further. 5. The proposed secure cryptosystem can be implemented in hardware for achieving practical applications, like mobile encryption, or virtual private network (VPN) application

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Other Titles التشفير وامن الشبكات : التقنيات والخوارزميات
Issue Date 2015

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