الفهرس 
Chapter 1: IntroductionOnly 14 pages are availabe for public view
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Abstract
Technology is widely used in everything around us, and therefore it has become one of the necessities of life. Regarding both software and hardware, security is the main factor in the modern internet environment. It is very needed to protect data privacy from being hacked and prevent them from being stolen by someone who can use them for malicious purposes. This need encourages technology companies and researchers in the field of information security to continuously research and develop systems that provide security and confidentiality of information and data to users. Accordingly, the term encryption (mainly cryptosystems) appeared so that only authorized people can understand the sent data. Data is encrypted using a key agreed upon by the communication parties.
During the nineteenth century, Kirchhoff, who was a Dutch cryptographic designer formed the view that all cryptosystems should be made public and that the key itself should be entirely responsible for keeping the secrecy of the data, but the quick development of computing makes it is easy to break the cryptosystem using a brute-force attack. In this kind of attack, the data is decrypted using each key that the cryptosystem might employ till gaining a meaningful one. The smaller the key size, the easier for this attack to be performed. It is also worth noting that it is possible now to undertake extensive analysis on cryptosystems, exposing their flaws and proposing improvements. Data Encryption Standard (DES) is the first standard 56-bit secret key that is widely used as a symmetric key with a 64-bit block encryption/decryption algorithm. DES was broken by a brute force attack with a complexity of 255 and theoretical analysis revealed that it is also possible to break it using a differential cryptanalysis attack with a complexity of 247. Also, the 64-bit block size isn’t suitable anymore. Due to the promising trends of Deoxyribonucleic Acid (DNA) in cryptography, this thesis presents a DES-DNA based symmetric key block encryption/decryption algorithm called iEncrypt. iEncrypt has two mechanisms (i1Encrypt and i2Encrypt), each of them uses a 64-nucleotide secret key that makes the secret key of the proposed algorithm serves as a 128-bit secret key. The experimental works show that the two mechanisms of iEncrypt are secure against brute force attacks, as the complexity would be raised to 2112. Moreover, a reduced version of the proposed algorithm to 4-round shows the robustness of the first mechanism (i1Encrypt) against differential cryptanalysis attacks in addition to the infeasibility of attacking the second mechanism (i2Encrypt). As images have rich characteristics data and help in the statistical evaluation, so, they are used in performance analysis. Statistically, the encrypted images confirm the intractability of attacking both mechanisms of the proposed algorithm.
Keywords Cryptography; DES algorithm; Symmetric-key cryptographic; DNA computing; Cryptanalysis; Brute force attacks; Differential cryptanalysis attacks.