Matthew Russell Crank
|Op. System:||Windows XP/2000/98|
|File size:||1.39 MB|
Publisher description for Matthew Russell Crank
Crank, or the "CRyptANalysis toolKit", is a program designed to provide automated cryptanalysis of classical pen and paper cryptosystems (an example of which might be the Caesar cipher, where each letter is substituted by the letter three places along in the alphabet). Because the mechanisms for decryption (authorised or otherwise) are Similar to encryption, Crank also doubles as a cryptographic typewriter, where you can see messages being encrypted on the fly as you type. When attempting an automated attack, the task is viewed as an optimisation problem. The quantity to be optimised is the "plaintextness" of the, er, PlainText, the latter being computed from the ciphertext using an instance of a cryptographic system. This instance is a transformation (called a "transform" by Crank), usually specified by a key, that maps a text string to another text string. The optimiser works over the space of keys of the transformation, trying to increase the "plaintextness", or in Crank terminology, "fitness" of the resultant candidate decrypted plaintext. The method the optimiser uses to search the keyspace is called the "heuristic". The purpose of Crank is therefore twofold; first, to provide a Library of transform, fitness and heuristic "componants", and second to allow them to be combined together and used in the cryptanalysis of a cryptogram.