Crank is short for "CRyptANalysis toolKit", and its overall purpose is to
provide a powerful and extensible environment for solving classical
(pen-and-paper) ciphers, providing as much automation as possible. Classical
ciphers include common schemes like monoalphabetic substitutions, where each
letter of the alphabet is mapped to another (usually different) letter
consistently through the text. The first version of Crank is restricting
itself to these special ciphers. Other algorithms forever devoid of Crank's
attentions include Enigma, RSA, DES, MurkelFish, or anything else invented
after 1900.  They're hard(er).

WWW: http://crank.sourceforge.net/