What are some unsolved mysteries of World War II

Famous Enigma message cracked!

Vocational school teacher from Singen solves the most famous crypto puzzle of the Second World War - 17 years after its publication

From our guest author Klaus Schmeh

[datensicherheit.de, January 28, 2013] The deciphering of Enigma radio messages was of enormous importance to the British during World War II. In Bletchley Park at the gates of London, the government built a whole decryption factory out of the ground in order to be able to crack the intercepted messages of the Germans with the latest technology. The success was remarkable: the British code breakers solved radio messages on the assembly line without the Germans getting wind of it - an invaluable advantage in the war against Hitler.
To the annoyance of today's historians, British Prime Minister Winston Churchill had all the documents that had accumulated in Bletchley Park destroyed after the end of the war. As a result, the numerous radio messages that the British had intercepted and resolved were lost. Since the Germans only rarely archived their radio messages, only a few thousand encrypted original Enigma messages are known today - originally there were probably over a million.
The first who, out of historical interest, found some original Enigma radio messages and made them available to the professional world, was the Northern Irishman Ralph Erskine. In 1996 he published three Enigma messages in the journal "Cryptologia". It was about sayings that the British warship "Hurricane" had intercepted in 1942 from a German submarine. At that time, submarines used the particularly secure four-rotor Enigma (the standard model only had three rotors), which made it much more difficult to decipher these three messages.
In 2003, cryptology historians, Frode Weierud and Geoff Sullivan, set about deciphering original Enigma radio messages for the first time. Thanks to computer support, it was much easier for them than the Bletchley Park code breakers once did - but the task was by no means trivial. Weierud and Sullivan did not try the difficult four-rotor messages that the "Hurricane" had intercepted, but rather took a collection of about 800 common Enigma radio messages left by a World War II veteran. To date, they have resolved over 700 of these messages. The work is still going on.

Source: Michael Hörenberg

The deciphered Enigma message coincides with an entry in the submarine's logbook; it was broadcast on November 19, 1942. The British destroyer "Hurricane" overheard.

In 2006 the musician Stefan Krah started a project called "M4" in which he wanted to crack the three still unsolved submarine messages from the "Hurricane" ("M4" is the type designation of the four-rotor Enigma). He too was successful: with the help of numerous like-minded people who made computing time available, he was able to resolve two of the three radio messages with distributed computing software. On the third, however, he failed. This third message from the “M4” project developed into the best-known unsolved encrypted message of the Second World War. It reads as follows:


In 2012, Michael Hörenberg, a vocational school teacher from Singen (Konstanz district), joined the Enigma research community. With software he had written himself, he managed to crack numerous original Enigma radio messages. Hörenberg delivered his masterpiece (supported by his US colleague Dan Girard) on January 4th, 2013: He deciphered the famous third Enigma message of the "M4" project. "70 years after the message was sent and 17 years after it was published, the plain text is readable again," Hörenberg said enthusiastically to datensicherheit.de. The plain text is:


In a slightly more legible form, this means:
Boat clear. At "Schnoor" around Nov. 27, 60 cbm. Provisions until 20 Dec. Need glasses, 4 more clear. Stand Marquess. BB 25. Location like “Schaefer”. NW 5, 15 mb increasing, good visibility. From "Rasch".

The content is not a big surprise as it coincides with an entry in the submarine's logbook. However, this does not play a major role, because for a real code breaker the solution is at least as interesting as the solution itself. "When the first fragments of the plain text of an encrypted message can be seen, it is an indescribable feeling," reports Hörenberg. “The blood pressure rises, the heart begins to race. That drives you. ”The vocational school teacher does not want to rest on his laurels. His next project is expected to deal with the decryption of Enigma messages from the Air Force. Hörenberg is optimistic: "The first tests look promising."

© Klaus Schmeh

Klaus Schmeh is the author of the book “Not to crack”, in which the ten greatest unsolved puzzles in encryption technology are described.

Further information on the topic:

Breaking German Navy Ciphers
The Enigma Message Breaking Project (Michael Hörenberg's website on his Enigma deciphering projects)

Frode Weierud’s CryptoCellar
Cryptology and Its History (Frode Weierud's website for other Enigma deciphering projects)

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Klausi's crypto column
A blog about encryption codes and secret scripts by Klaus Schmeh