Cipher Type Detection

Manual analysis and decryption of enci-phered documents is a tedious and error prone work. Often—even after spend-ing large amounts of time on a par-ticular cipher—no decipherment can be found. Automating the decryption of var-ious types of ciphers makes it possible to sift through the large number of en-crypted messages found in libraries and archives, and to focus human effort only on a small but potentially interesting sub-set of them. In this work, we train a clas-sifier that is able to predict which enci-pherment method has been used to gener-ate a given ciphertext. We are able to dis-tinguish 50 different cipher types (speci-fied by the American Cryptogram Associ-ation) with an accuracy of 58.5%. This is a 11.2 % absolute improvement over the best previously published classifier.