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|a With the ever-expanding use of technology for communications, the demand for strong cryptographic methods is continually growing. The implementation of cryptographic algorithms in modern networked systems is crucial to ensure the security and confidentiality of data. Standardized encryption algorithms have emerged to allow users and developers a quantifiable and thoroughly tested level of security within their systems. While much research has been done to improve the security of traditional ciphers such as the Advanced Encryption Standard (AES) and the now-defunct Rivest Cipher 4 (RC4), there are opportunities for the development and improvement of alternative ciphers based on graphic methods. Encryption using graphic methods, such as Visual Cryptography (VC) and Elliptic Curve Cryptography (ECC), give high levels of security, and demonstrate alternative approaches to achieve secure methods for the ever-expanding online world. This thesis proposes an alternative word-oriented symmetric stream cipher based on graphic methods called Coordinate Matrix Encryption (CME), which offers quantifiably high levels of security and a non-singular mapping of plaintext to ciphertext. The focus of this thesis was to explore the security offered by alternative graphic methods, in comparison to traditional classical methods, as well as the difficulties faced in implementing these alternative systems. It is hypothesized that graphic-based methods would offer higher levels of security with lower overheads than classical methods, and that the proposed CME system would prove secure against attack. The proposed system was implemented in Java along with four comparable algorithms, both graphic-based and traditional, which were AES, RC4, ECC, and VC. The algorithms were all tested for security and efficiency, and the comparative results show the high levels of security achievable by alternative graphic-based ciphers. The resistance of the proposed 8-bit CME system to brute force attacks was shown to be 157,899 orders of magnitude higher than that of a 128-bit key in traditional ciphers such as AES. Examination of the avalanche effect of the CME scheme showed that less than 0.5% of all bytes within the ciphertext remained in the same position when a single bit of the plaintext was altered. While the RC4 scheme offered the best efficiency in terms of time required to encrypt and decrypt the data, the CME scheme had lower memory requirements and was faster in the setup execution. Further research into alternative graphic methods is required to explore the applications of alternative systems such as CME. The security offered by the proposed CME scheme makes it an ideal candidate for post-quantum cryptographic research. The system?s alternative key structure and non-singular mapping allow for resistance to known and chosen plaintext attacks, and these features require further exploration. Further comparative analysis between traditional and graphic-based ciphers is required to determine whether alternative graphic methods are able to offer higher security for lower overheads. Optimization of the CME scheme requires further testing, to ensure it has competitive advantage, and it is able to be implemented in application development. There is currently little standardisation in stream ciphers to replace RC4, and as such the opportunity exists for an optimized version of CME to assist in this particular space in applications such as TLS that utilize stream ciphers for encryption on a day-to-day basis.
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