An interactive cryptanalysis algorithm for the vigenere cipher

Abstract

Though it dates back centuries, Vigenere Cipher is still a practical encryption method that can be eficiently used for many appli- cations. We have designed and implemented an interactive cryptanalysis software based on the Kasiski test, and a novel use of the Index of Coin- cidence (IC) concept. Our results show that cryptanalysis is possible for very short text lengths where classical cryptanalysis methods fail. Furt- hermore, we have observed that our software which is designed to work on English based ciphertexts, can be successfully executed on ciphertexts based on other languages. Along the way, we also compute and report the IC values for Turkish and some other languages under a difierent number of enciphering alphabets.