Did the crack of Enigma shorten World War II

How the code of the legendary Enigma machine was cracked

It's probably one of the most famous devices in history: the Enigma. This encryption machine and the struggle to crack its code have been immortalized in several novels and films - most recently in the movie "The Imitation Game". No wonder: for decades, the code of the Enigma machine was considered to be absolutely unbreakable. Because in contrast to classic encryption methods, with the Enigma code, even sophisticated language analysis did not get you any further.

The reason for this is the complex functionality of the Enigma, which combines several classic encryption techniques. In doing so, it does not follow a logically recognizable principle, but rather generates an apparently almost random encryption.

How the Enigma works

The heart of the Enigma are three, later four, rotating rollers with the 26 letters of the alphabet. If you enter a letter, the rollers are rotated against each other in a certain way according to their electrical wiring. This results in the encrypted letter. Since the position of the reels changes with each entry, an "E" is encoded as a different letter every time, even within the same text. To make the whole thing even more complicated, the Enigma reels are inserted into the housing in a new configuration each time they are used, which means that the encryption is constantly changing. You can only get the plain text of a message encoded with the Enigma if you have an Enigma yourself - and know the current configurations.

This machine was developed by the German engineer Arthur Scherbius. On the basis of a previous version developed in the USA, he constructed an encryption machine based on the rotor principle for the first time in 1918 and applied for a patent. After initially being unable to convince the military of the usefulness of this machine, Scherbius first presented his "writing Enigma" at trade fairs. It was not until 1926 that the German Navy decided to use the Enigma to encrypt radio messages at sea. During the Second World War, this cipher machine became the heart of military communications, both on land and at sea.

Bletchley Park - the code breaker headquarters

This is exactly a big problem for the Allies. Because despite all their efforts, their cryptographers fail to decipher the radio messages from the German military. As a result, they do not know where attacks by German submarines or warships are threatened in the Atlantic. As a result, supply and troop convoys are repeatedly sunk en route from the USA to Great Britain.

The British mathematician Alan Turing made the breakthrough. From 1939 he worked in Bletchley Park, the secret headquarters of the British code breakers during the war. Turing developed an electromechanical machine, the so-called “bomb”, on the basis of a simpler pre-model that was constructed by Polish mathematicians. The device, so named because of its ticking noise, narrows the possible solutions of an Enigma cipher to just a few. A bomb consists of dozens of rotating drums with letters that trace the various possible positions of the Enigma rotors.

Help from the weather report

However, in order to tackle the Enigma code, the bombs also need a first starting point - a word or part of a word from which the decryptor could guess what it meant in plain language. This is where the cryptographers in Bletchley Park, sweating over the codes, benefit from a weak point in German radio messages: They often contain phrases that always appear in the same form and often in the same place in the radio messages. These include, for example, expressions such as "Oberkommando" or the phrase "Heil Hitler", which is often at the end of the message. In addition, the German radio operators send the weather report at the same time every day - and the word "weather" is prominently placed in it.

Based on these weak points, Turing and his team succeed in guessing the possible positions of the Enigma rollers. However, this requires tedious and time-consuming detailed work first with paper templates and then with replicas of the Enigma rollers. At first, however, the Enigma code does not seem to be deciphered despite the promising starting points.

The breakthrough: The Enigma is cracked!

But then came the breakthrough: On January 17, 1940, the cryptologists in Bletchley Park succeeded in decrypting an Enigma message for the first time - initially still by hand. As a result, they still need days, sometimes even weeks, to report - this is far too slow for the rapidly advancing war. This is where Turing's "bombs" come into play. You automate the laborious trying out of the roller positions and can thus test the 17,576 possible positions of an Enigma roller set in around 20 minutes. Bit by bit, the code breakers from Bletchley Park succeed in listening to the radio traffic of the German military faster and better.

This breakthrough in the decryption of the Enigma is ultimately decisive for the war. Because only by reading the radio messages can the allied troops understand the movements of the German submarines and thus win the submarine war. Knowledge of German radio messages also plays a decisive role in important battles in the Mediterranean and when the Allies land in Normandy.

Ultimately, cracking the Enigma code probably shortened World War II by years - and saved thousands of people from death on the battlefield or in the wreckage of bombs.