Breaking German Wehrmacht Ciphers


This is the Web Portal for our ongoing projects of breaking German Wehrmacht ciphers. Here we will try to keep you informed about what is happening in this exciting field. We will report both on our own work as well as giving links to other external projects also attempting to break original and authentic German Wehrmacht messages.

Our project, which we call Breaking German Army Ciphers because the messages were enciphered on the 3-wheel German Army Enigma machine, started in earnest when we broke the first message in March 2003. A selection of these messages had been handed over to use already in February 2001, but it was first in 2002 that we really started to explore the possibility of attacking these messages. The problems we faced was an order of magnitude greater than those Bletchley Park (BP) usually were facing. When they intercepted enemy messages they usually had an idea of their origin. They would know from where the messages were transmitted due to direction finding and they would also usually be able to tell if they were Army, Navy or Air Force (Luftwaffe) messages. Sometimes they would even be able to make fairly accurate guesses about the possible contents. None of this information was available to us, however we made an accurate guess that they were German Army messages from the look of the messages themselves. One advantage we had over BP was that the messages came to us on original German message forms. Therefore we usually did not have to worry about transmission garbles, even if later on we also discovered that the messages had garbles due to erroneous transmission or reception on the part of the German radio operators. However, we faced the problem of deciphering the radio/cipher operators hieroglyphs which sometimes meant that during the transcription process to convert the messages from the message forms to electronic copies we introduced our own garbles.

NB! The information on this page is not entirely up-to-date with respect to which messages have been broken etc. Hopefully this will be corrected in the not to distant future. In the meantime we invite you to read our latest contribution to the knowledge of breaking authentic Enigma ciphertexts. You find a link to our latest Cryptologia article, Modern breaking of Enigma ciphertexts, below together with a link to a Web page with further detailed information about the broken German Army messages. The article is specially interesting for those who want to understand the finer details of modern Enigma codebreaking and especially how to attack short Enigma ciphertexts.

We are now able to let you discover all these events and more in the article that we wrote for the journal Cryptologia. The Editor-in-Chief, Professor Brian Winkel, and the Cryptologia publisher, Taylor & Francis, have agreed to exceptionally allow us to post the complete article on the Web. The article is available for download directly from the Cryptologia Web page of Taylor & Francis.

In our article you will see we offer the readers five sample Enigma ciphertext messages as a challenge. The messages and the necessary language statistics are available for download here.

To help explain the rather intricate keying procedures used by the German Army and Air Force we have created an Enigma Timeline showing these procedures. This shows the main developments and it will be expanded with more special procedures at a later stage.

To further show the scope of our project, Breaking German Army Ciphers, you can examine the number of message from 1941 and 1945 that have been broken and transcribed so far. For the 1941 messages in the September Batch B we already have the keys but have not yet had the time to decode and correct the messages for errors etc. For the 1945 messages there is about 50 messages which still have to be decoded and corrected, but the keys have been broken.

We plan to release a selection of the broken German Army messages originating with SS units from Heeresgruppe Nord taking part in Operation Barbarossa, the attack on the Soviet Union, and which cover the period June to October 1941. Here is the first instalment.

We already have released sample messages from the second set of messages which are from April 1945 and which originate at the concentration camp Flossenbürg.

We will also try to explain in more detail some of the cryptanalytical techniques and algorithms like hill climbing.

As a challenge and as our contribution to keeping the M4 Message Breaking Project (see below) alive, we are releasing two sets of unbroken Enigma messages from the German Army message pool.

We also want to give pointers to other external projects attempting to break German Wehrmacht ciphers. The most exciting project at the moment is Stefan Krah's M4 Message Breaking Project. They have just managed to break their first German Navy message, a message enciphered on the 4-wheel Enigma machine. The project is using similar cryptanalytical techniques to what we are using, statistical methods and hill climbing, but contrary to our codebreaking project they are using a network of distributed computers. More details about this project and its achievements can be found below.

We have made an analysis of the first message broken by the M4 Message Breaking Project to determine if the break was lucky, easy or hard. Our analysis is given here. You also will find Geoff Sullivan’s paper on how to break these messages with the Turing-Welchman Bombe.

Ralph Erskine, a historian who has studied and published extensively on World War II German Naval cryptology, has recently released more Enigma M4 messages which hopefully will keep the M4 Message Breaking Project going. He has also written a detailed explanation on how Bletchley Park’s Hut 8 (Naval Enigma) broke the Enigma keys Dolphin and Shark. Both contributions are available here.

Other Decoding Projects

We should like to take this opportunity to make a general request for more German Naval ciphertext messages. If anybody should know of such messages can you please take contact with me, E-mail: cryptocellar-at-gmail-dot-com  (Please replace –at– with ‘@’ and –dot– with ‘.’ )

For those of you who feel you would like to know more about the Enigma machine and how it was used during the Second World War we have added a few links where you will find more information about this most interesting subject.



Creative Commons License This work is licensed under a
Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
The material described on these pages is created, collected, edited and published
by Geoff Sullivan & Frode Weierud, © March 2006

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