Turing Bombe Simulation:

Instructions: Type the crib into the "Plain text" field and enciphered data into the Cipher text field of the applet and press the Start button.

A crib is basically a line of text where you know both the encrypted and unencrypted version. The Bombe then tries to find the Enigma settings that could produce the encrypted text. This should reveal the remainder of a message. Sometimes it works; others it doesn't. This is because codebreaking is an imprecise art.

We recommend that you use the Example button and then press Start. This should produce a drop of 123-CBA (AH) (LY) (NS) (OR). The full test takes about 1 hour and 45 minutes on a 100 Mhz Pentium using IE 3.0.

A drop consists of the rotors used, their initial settings, and the plugboard settings. The 123 corresponds to rotors, the CBA the initial settings, and the pairs of letters to plugboard settings. Using this, it is possible to decrypt an entire message even if you only know part of the plaintext.

The "Unknown ring setting" option represents the way the real Bombe worked. In this mode the crib being tested will not work if either the medium or slow rotors moved when the corresponding cipher text was produced. A good solution to this problem is to chop the crib into two halves. One of two halves should be free of middle and fast rotor movement.

The other option is just for fun. The rotors can move whenever and it will not matter, but all the rings must have been set to A.