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Automatic Cryptanalysis : A Dictionary Based Method for Solving Mono-alphabetic Substitution Cryptograms Final

Declaration All sentences or passages quoted in this dissertation from other people's work have been specifically acknowledged by clear cross-referencing to author, work and page(s). Any illustrations which are not the work of the author of this dissertation have been used with the explicit permission of the originator and are specifically acknowledged. I understand that failure to do this amounts to plagiarism and will be considered grounds for failure in this dissertation and the degree examination as a whole. Abstract This paper introduces some of the best-known encryption techniques and goes on to detail methods successful in breaking these techniques. The aim of this is to highlight that many systems believed to be secure are not necessarily secure, and, for those that were secure when first invented, the current progress of technology has changed this. A method capable of automatically deciphering messages produced using the mono-alphabetic substitution cipher is designed and implemented, with the outcome of a fully working and successful system. One that actually exceeds the requirements originally laid out during its initial conception. This system differs from many similar techniques in that it avoids the use of statistical analyses. Though successful, it appears obvious that this system could still benefit from the inclusion of such techniques; suggesting a hybrid method combining the two approaches. A number of improvements are suggested for the system and the possibility of extending this method further, to include the solution of poly-alphabetic substitution cryptograms, is examined.