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A reverse-engineered codebook from World War I

Von / 2. Juli 2017 / 18 Kommentare
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In the British National Archives I found a small codebook from World War I. Apparently, it contains a German code that was reverse-engineered by British codebreakers. Many details about the origin of this codebook are unclear.

British codebreakers played an important role in World War I. For instance, the deciphering specialists of the legendary Room 40 broke a telegram sent by German State Secretary for Foreign Affairs, Arthur Zimmermann, to Mexico, which finally convinced the US government to join the war on the side of the British.

 

A brief guide for crypto analysis

Last week I went to the British National Archives in London. When I searched for documents that had a relationship to cryptology, I came across a German codebook from World War I (ADM 137/4691). Described as a “Brief guide for crypto analysis”, this codebook is dated December 1916. It is available here for download.

The code described in this book is German. It was apparently used by the Germans during World War I. However, this codebook is not an original, but was reverse-engineered by British codebreakers. It is not known how the British gained knowledge of this code. Maybe a spy or a prisoner of war supported them.

The following page is a typical one. It shows three letter codegroups standing for a German expression each:

Signalbuch-01

The cleartext words, like “Kurs” (course), “aufgestiegen” (risen), and “Motorprobe” (engine test), remind me of a U-boat.

I wonder what a “Zepp” is. Does a reader have a clue?

The following page contains a number of geographic expressions (including the word “North Sea”):

Signalbuch-03

Most the geographic expressions refer to places in or at the North Sea. The following page contains the cleartext word “Jade”:

Signalbuch-02

The Jade is a river in northwestern Germany. It flows into the Jade Bight, a bay of the North Sea.

All in all, it is clear that this codebook was used in the North Sea area. As it is a quite simple code, it was probably not intended for the highest security level.

 

The compass diagram

The most striking page in the codebook is the last one. It shows a code expression for every compass direction:

Signalbuch-Windrose

According to this diagram, the codegroup for southwest is SW, ESE represents east-southeast. If there was no additional encryption, this part of the code was pretty weak.

If a reader can tell more about the background of this codebook, please let me know.


Further reading: How FBI codebreakers found out what “K1, P2, CO8, K5, P2” means

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Kommentare (18)

  1. #1 Tony
    2. Juli 2017

    Hi Klaus,
    In answer to your question: I would think that “Zepp” would be a reference to Zeppelin, a type of rigid airship named after the German Count Ferdinand von Zeppelin, WIkipedia has more information here https://en.wikipedia.org/wiki/Zeppelin
    Tony

  2. #2 TWO
    2. Juli 2017

    Zepp(s) is zeppelin

  3. #3 TWO
    2. Juli 2017

    I dont see any code expressions on the compass rose?

    To what specifically are you referring?

  4. #4 Norbert
    3. Juli 2017

    Zepps = Zeppelin airships?
    I can’t see anything code-like in the compass diagram, which also doesn’t look German to me. ESE is just the common English abbreviation for east-southeast, isn’t it? The German counterpart would be OSO.

  5. #5 David Wilson
    3. Juli 2017

    Zepp == Zeppelin, maybe, seeing as it’s World War 1 era?

  6. #6 Thomas
    3. Juli 2017

    As the “Brief guide for crypto Analysis” dates from Dec. 1916, it could have been a reconstruction of the “Allgemeines Funkspruchbuch” from 1916 which was found in the wreckage of Zeppelin L32, shot down over England on Sept. 24, https://books.google.de/books?id=CVNzAgAAQBAJ&pg=PA264

  7. #7 Thomas
    3. Juli 2017

    The Room 40 exposition in Betchley Park has a working copy of the reconstruction of the “Allgemeines Funkspruchbuch” found in the Zeppelin (https://issuu.com/cultureshockmedia/docs/bletchley_park_magazine_____issue_4/26). I might be worth comparing it to the “Brief guide”. Wether the Bundesarchiv can provide a copy of the Funkspruchbuch from 1916, I don’t know.

  8. #8 Jerry McCarthy
    England, Europa
    3. Juli 2017

    Abo…

  9. #9 Jerry McCarthy
    England, Europa
    3. Juli 2017

    #4 “ESE is just the common English abbreviation for east-southeast, isn’t it? ”

    Yes, it is….

  10. #10 Ulrich
    Berlin
    3. Juli 2017

    Interesting! Nothing much to decode, since 99% is German plaintext (2- to 4-letter groups, comparable to the hotel- and banker’s telegraphic codes used around 1900). Sources were maybe discoveries of code-books in shot-down Zepps plus British decryptions of intercepted wireless messages.This is suggested by entries on the page entiteled “PART”, (1) where various Zepps are named, (2) the word PART bears no number as if there were more to come, (3) the bottom of the page bears some entries half-solved or unsolved. – The originator of the booklet is surely British (with superb knowledge of German), see the few added notations in English (“Common 2 letter groups”; “every man his own pundit”). “Pundit” is, by the way, army slang stemming from India [Sanskrit], meaning an expert or ironically a “know-all” (Besserwisser). – There is nothing hidden in the compass card, maybe just German Zepp-readings translated into English usage.

  11. #11 Thomas
    3. Juli 2017

    An example:
    In the ‘Brief guide’ the german word ‘abfahren’ is coded with a letter group beginning with ‘ac’ as it is in the ‘Allgemeines Funkspruchbuch’ from 1917, captured from U-110: https://germannavalwarfare.info/02subm/01/afb.html (unfortunately only one page of the dictionary part is shown).

  12. #12 Torbjörn Andersson
    Kalmar, Sweden
    3. Juli 2017

    The 3-letter groups are taken from the “SKM” (Signalbuch der Kaiserlichen Marine), also known as the “Magdeburg Code Book”. The booklet looks like an aid when reconstructing the superencipherment used with this code, listing common SKM code groups by their last letter. In it’s basic form, SKM was far too simple to offer any security, so the groups were enciphered, using a simple substitution cipher, prior to transmission. This cipher had to be broken on – I believe – a daily basis, in order to arrive at the proper code groups listed in the SKM. Having commonly occuring code groups listed in a booklet, would help with that.

  13. #13 Thomas
    3. Juli 2017

    @Torbjörn Andersson
    If I’m not mistaken, there are letter groups that differ from the SKM, at least from the online available Magdeburg version 1913 (https://germannavalwarfare.info/02subm/01/skm.html).
    For example: ADW in the brief guide stands for ‘abholen’, in the SKM for ‘anschrauben’. AFG: b.g.: ‘ablösen’, SKM: ‘anstecken’. AHU: b.g.: ‘abschießen’, SKM: ‘Antwort durch F.T.’ Maybe you refer to another version?

    Concerning the ‘Zepp. reports’ part containing weather vocabulary:
    Also on Sept. 24 1916 ( the brief guide dates from Dec. 1916) another Zeppelin (L33) was shot down over England, this yielded the weather code (see Grant, U-boat hunters, p. 35).

  14. #14 Torbjörn Andersson
    Kalmar, Sweden
    3. Juli 2017

    It’s the same edition Thomas, but you have to be careful and distinguish A’s from Ä’s.
    The SKM uses ‘umlauted’ letters (Ä, Ö, and Ü, printed in a Gothic font), beside ordinary A’s, O’s and U’s (as well as some greek letters, alpha and gamma). So ‘ÄDW’ means ‘anschrauben’, and ‘ADW’ – without dots on the A – means ‘abholen’.
    In the British manual, the ‘umlauted’ letters have a horizontal bar on top to distinguish them from the ordinary ones – it is an easy thing to overlook.

  15. #15 Thomas
    3. Juli 2017

    @Torbjörn Andersson
    Yes, I overlooked the Umlaut transcription. But still there are differences: In the brief guide ÄE stands for ‘Aufklärung’, whereas the extract of the (alphabetically arranged) SKM ends with ÄJ groups for ‘Anzug’, so that ‘Aufklärung’ must be represented by a letter group farther in the alphabet. Maybe the (unknown) “Allgemeine Funkspruchbuch” from 1916 contained modifications of the SKM/additional entries that became part of the brief guide? Have you found more extracts of the SKM?

  16. #16 George Lasry
    4. Juli 2017

    This is FVB. I have a copy of it, and Linie appears as CDZJ, as in the picture above. DKGA is Nordgruppe.

  17. #17 Thomas
    5. Juli 2017

    Thus it is probably based on a compilation of the various codebooks in use, https://books.google.de/books?id=aQJ9E78e7uEC&pg=PA36

  18. #18 Ian
    17. September 2019

    I am amazed that nobody has seen the obvious in the compass rose. I think what the German authors had intended is that you follow each line to its reverse position, thus giving a direction totally the reverse of where you are actually going, or you could follow the equivalent line in a different quadrant, thus totally obscuring your actual location, so counting back one direction in Quadrant NE and counting back one direction in Quadrant NW, the heading E6N would become N6W for example. Providing your HQ knew which line you were following on a particular day or week, you could create a good ruse in your communications. To really obfuscate your direction, you could even vary this code by counting 3 compass directions forwards or backwards in another quadrant for every one direction in the actual quadrant. Providing HQ and boat were “on the same page” in their agreed coding, the message would make perfect sense to them, but the directions would be totally obfuscated for any allied forces listening in.