Abstract

Abstract: Frequency analysis is the fundamental cryptanalytic technique besides brutal force, threat, blackmail, torture, bribery, etc. [1]. Conventionally, it is applied on monogram, bigram and trigram together with anagramming technique [2]. The efficiency of anagramming depends on the cryptanalyst's depth of knowledge in different language features. Hence anagramming is a trial-and-error approach due to huge deviation in different fields, e.g. military, diplomatic, commercial, legal and daily languages. The frequency fluctuations among the normal frequency order of the characters trigger the crossover problem for monogram frequency analysis. Meanwhile bigram and trigram frequency analyses are found to give little help. Higher orders are unlikely to be useful. In 1994, George Hart introduced a novel frequency analysis approach based on word frequency to decode the enhanced frequency analysis for systematic decryption of English ciphertext [3]. The proposed protocol uses combined techniques of monogram frequency analysis, keyword rules and dictionary checking. It is successfully tested faster on monoalphabetic substitution cipher. Moreover, it solves the weakness of Hart’s approach for complete failure when neither top 135 words is found in the ciphertext. Further extrapolation is expected to be applicable to other cryptanalytic algorithms and languages.

Citations