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A codebook is a very old and effective method for concealing the contents of a
message.
Initially, codebooks were not meant for the encryption of a message, but simply
to make the distribution of messages more efficient when using
morse codes
over telegraph lines or radio.
In many cases, frequently used words or even complete sentences were replaced
by three or five-letter abbreviations.
This would make it easier (and cheaper) to send a message over a long distance.
The international Q-Codes are a good example of this.
During WWII, codebooks were often used to encipher a message, sometimes in
addition to other cryptographic methods, such as Enigma
or hand ciphers.
Cracking a codebook is a difficult task for a code breaker, but once the
codebook is captured by the enemy, the secret is completely given away.
They could therefore be classified as Security by Obscurity.
On their own they aren't very safe, but when used in combination with other
cipher methods, they can be a real nightmare for the average code breaker.
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Internationales Signalbuch 1931
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A good example of a very efficient codebook, is the German book shown
here: Internationales Signalbuch 1931 (International Signals Book 1931)
Band II, Funkverkehrsbuch (Volume II, Radio Traffic Book).
It was published by Walter de Grunter & Co under the authority of the
Reichsverkehrsministerium (National Traffic Ministery).
Before WWII, book like these were widely used for international (radio) traffic.
More detailed images below.
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During WWII, the German Armed Forces used this book in addition to other
cipher methods. It made messages shorter and hence more effecient, but
also created an extra layer of obscurity in an encrypted message.
The full title of the book is Funkverkehrsheft für die Küstenverteidigung
(Radio Traffic Book for Coastal Defence). It contains a number of entries that
can be altered manually. The book shown here was used by the Germans for the
defence of the Dutch coast. The names of cities and towns are written in the
book by pencil.
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Funkverkehrsheft courtesy Arthur Bauer
[1]
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During WWII, the German Kriegsmarine (Navy) used a variety of codebooks
in combination with their M4 Enigma machine.
The German Naval message procedures were very complex and caused the
code breakers at Bletchley Park many headaches.
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The images below show some German Navy code material, used during WWII.
The codebooks of the U-Boot department of the Kriegsmarine were printed
with red water-solvable ink on pale red paper.
When left behind in a sinking U-Boot, the codebooks would wipe themselves
automatically, which is why it was so hard to capture them.
The caption on the top of the page on the right, reads:
Vorsicht! Wasserlöslicher Druck! (Careful! Water solvable print!).
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The procedures consisted of Enigma key settings, Kenngruppenbuch, Kengruppen tables,
Letter-pair swap tables, Short Message books, Weather Code books, etc.
Dirk Rijmenants in Belgium has described the procedures of the German
Wehrmacht and Kriegsmarine in great detail on his website
[2]
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Codebooks courtesy Arthur Bauer
[1]
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© Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Friday, 01 February 2013 - 15:04 CET
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