Historical Info:

Marian Rejewski Link
(Fundamental research)

Alan Turing Link
(Improved the Polish Bombe)

Gordon Welchman Link
(Inventor of the diagonal board)

How to break the ENIGMA M4 code of U534

By Michael Hörenberg

This article describes the approach in deciphering the "U 534" messages.

Cryptanalysis of the Enigma machine:

1. Step: Determine the "key of the day" (Tagesschlüssel) for 1.May 1945 with the M4 WinEnigma Turingbombe software (a slow procedure). The Bombe was originally a ticking electromechanical device, which was named after Alan Turing, but invented by Marian Rejewski.

2. Step: Determine the correct wheel position and hillclimbing the missing plug(s) with the TBreaker software (a fast procedure).

3. Step: Breaking all Enigma messages (Nachrichten) with the same "key of the day" by determining the correct wheel position (a fast procedure).

A Turing Bombe run involved a cryptanalyst first obtaining a crib — a section of plaintext that was thought to correspond to the ciphertext. Finding cribs was not at all straightforward; it required considerable familiarity with German military jargon and the communication habits of the operators.

The TB´s used during WW2 could not detect rings and turnovers. Because of that, they were limited by the number of characters. A weak or short crib produced many false stops. WinEnigma can detect Mid-Rotor Turnovers and the fast ring! Because of that, Michael´s WinEnigma simulation software can use very long cribs.

The unique performance of WinEnigma:
Bild "Turing Bombe crack"
First test:
A break of the famous LOOKS message from the M4 Project.
At the original key settings. The TB used a 23 character wide crib!
The crib also had a Mid-Rotor turnover!
--> WinEnigma finds the correct fast ring!

Bild "Turing-Bombe long crib"
Second test:
Now the LOOKS message is encoded with Rotor Order 128.
The message now has 2!!! Mid-Rotor turnovers in the crib,
because the M4 rotors 6-8 had 2 notches.
The TB used a 23 character wide crib! and the TB find the correct fast ring!

The software needs a lot of computation power! WinEnigma has to check all UKW B C and Greek rotor beta/gamma combinations (1344) at all possible wheel positions (456976). The TB can also find the fast ring! (26x slower)  --> 15.968.569.344 Tests.

Time: 240 hours with a 4 core CPU (2.4 GHz) --> For every single CRIB test.

But IF U534 used regular M4 ENIGMA machines and if there are no garbles in the cribs, WinEnigma will crack the KEY OF THE DAY!

With the correct daily key (Plugs, Wheel Order, Rings) all messages will break by Hillclimbing/Brute-Force within seconds. (Wheel position search).

Michael use(d) 112 CPU cores. INTEL XEON 4 core and INTEL CORE DUO. The estimated time for a CRIB run is about 8 hours.

Bild "Software Turing Bombe"
INTEL XEON Workstations processing the WinEnigma software