A Novel Way of Decrypting Single Columnar Transposition Ciphers

Single columnar transposition is an encryption technique used in text encryption to produce cipher text which is a permutation of its original text. In this study, cryptanalysis of Single Columnar Transposition is performed and the novelty in this research is the cipher text given as only input, is deciphered without knowing the encrypting key to reconstructing the plain text before encryption. The key length currently unknown, can be determined as a factor of the cipher text length, thereby reducing the number of computations for decryption. The finite set of key lengths determined will be used to construct the matrix for decryption. The novelty in this research is the use of the longest prefix match which matches the longest word and checks the word if it exists in the English dictionary. If all the words that were constructed from the decryption by going through all the permutations of the key length determined by the matrix dimension earlier, we would get the plain text. This research performs a time analysis of the algorithm, including the worst-case and best-case scenarios for a particular ciphertext across key lengths. The keyless decryption time vs the key length, the graph is exponential in the experiments conducted with limited computing power. With better computing systems, the algorithm can be improved and restructured to give a linear time graph. The study can also be extended to include other languages, variable text sentences, and paragraphs in a document.