M.Sc. (Computer Science) / The main themes of this thesis are the characteristics of natural language, cryptographic algorithms to encipher natural language and possible figures of merit with which to compare different cryptographic algorithms. In this thesis the characteristics of natural language and the influence this has on cryptographic algorithms is investigated. The entropy function of Shannon is used extensively to evaluate the different models that can be constructed to simulate natural language. Natural language redundancy is , investigated and quantified by the entropy function. The influence this redundancy has on the theoretic security of different algorithms is tabulated. Shannon's unicity distance is used as a measure of security for this purpose. The unicity distance is already shown at this early stage to be not a very accurate measure of real (practical) security of cryptographic ciphers. The cryptographic algorithms discussed in this thesis are arbitarily divided into three groups: classical algorithms, public key algorithms and computer algorithms. In the classical algorithms cryptographic techniques such as transposition and character substitution are included. Well known ciphers such as the Playfair and Hill encipherment schemes are also included as classical cryptographic techniques. A special section is devoted to the use and cryptanalytic techniques of polyaphabetic ciphers. The public key ciphers are divided into three main groups: knapsack ciphers, RSA type ciphers and discrete logarithmic systems. Except for the discrete logarithmic cipher several examples of the other two groups are given. Examples of knapsack ciphers are: Merkle Hellman knapsack, Graham-Shamir knapsack and Shamir's random knapsack.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:4382 |
| Date | 18 March 2014 |
| Creators | Van der Bank, Dirk Johannes |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Johannesburg |
Page generated in 0.002 seconds