I am trying to understand the conditions necessary for one of the Bletchley Park bombes to stop. Let me give an example.
I have been experimenting with Enigma machine and bombe simulators to try to understand better how the bombe works.
Using a standard three rotor Enigma machine set up as follows:
- Rotors IV-I-III,
- starting with QLH
- rings set to AAA
- with plugs EL GK US XZ WI NV FD BY MC PQ
The following plaintext WETTERVORHERSAGE becomes the following cryptotext RRHKJKNJXEUWNFOT (see enigma simulator) .
Using this as a crib, the menu that this produces has three loops (REHTK, EHT, RETK) and a click (loop of the two letters WR), which is pretty good as a crib as this means that the bombe then returns far fewer false stops.
When I plug this crib into the following bombe simulator (where all rings are set to A) I get a collection of about twenty stops, one of which is the correct one.
So my question: what is the condition that stops a bombe that is satisfied with respect to the crib menu?
My understanding is that the back of the bombe is set up to simulate the menu and then the bombe is switched on, stopping through a short circuit when, well, when what?
I tried to use the first false stop that the bombe simulator gave me to understand: 231-YAL. So in particular, my question can be applied to this situation. What is it about this set-up that would stop the bombe with the given crib-menu?
What I did notice in this configuration is that the click is correct with respect to the letters M and T (indicating that there should be plugs WM and RT) BUT the remainder of the loops do not match.