An Automated Approach to Solve Simple Substitution Ciphers

This paper reports a method to automatically solve simple substitution ciphers where the message length is about 160 characters and the space character is suppressed during encryption. Patterns available in the crypt are used as opening points. With the help of a dictionary system, words are fitted at these points after suitable filtering. Subsequently, a tuple generator-cum-selector is used to select a meaningful tuple of words for decoding the crypt. During test runs, 70 out of 100 randomly chosen messages were solved to as sufficient a degree as to facilitate manual completion. Manual completion was found to be fairly simple when the algorithm had correctly identified 70 percent or more of the character positions. The time required for the algorithm to reach this stage was, on an average, about twenty minutes on a standard personal computer.