Automated cryptanalysis of substitution cipher using Hill climbing with well designed heuristic function

Abstract

In this paper, we propose new method for automated cryptanalysis of substitution cryptosystem using Hill climbing algorithm. New heuristic function is proposed in order to drastically improve overall fitness of the standard Hill climbing algorithm. Several fitness functions have been tested and we try to detremine which of them perform better in specific situations using our suggested time-dependent measure goodness. We conclude which of those functions should be used in case we are dealing with short or long texts.