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Substitution and Transposition Cipher
The Caesar Wheel was a training tool for cryptographers and cryptanalysts
at the Dutch Army Intelligence Unit. It was developed and built for
instructional purposes by the Centrale Werkplaats Instructiemiddelen
(CWI) in the early 1970s. It consisted of three independently movable
concentric wheels, each with a full Latin alphabet on one side
and a Cryllic one on the other side.
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The image on the right shows the Latin side of the Caesar Wheel.
It has a diameter of approx. 14cm, which is about the size of a hand.
The outer disc is solid and contains the alphabet written as letters (A-Z)
and numbers (0-25).
High-frequency letters (i.e. letters that appear often in common language)
are printed in red.
At the center is the inner ring, which consists of a a transparent
plexiglass disc with the letters of the alphabet printed on it.
The disc is held in place by a bolt at the center. The center disc can
be moved independently from the outer ring.
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In between the outer ring and the inner disc is a red ring
with letters on a black background. The letters
are removable
and can be mixed at will,
allowing the wheel to be used
as a transposition cipher [1] but also as a
subsitution cipher [2] simply by configuring it.
In order to configure the alphabet, the inner disc has to
be removed first.
This is done by releasing the bolt at the center.
The middle ring can be rotated independently from the other two rings,
by holding the device in one hand,
whilst moving the notch at the letter G
with a finger of the other hand.
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As the Caesar Wheel was developed during the early 1970s, at the height
of the Cold War, the other side of the disc
had a full cyrillic alphabet.
As the cyrillic alphabet is larger than the latin alphabet, there are
31 letters on each ring (А-Я), numbered 0-30. Like with the Latin
alphabet, the high frequency letters (АВДЕИ...) are marked in red
on all three rings.
The letters on the middle ring can be removed and mixed at will.
The middle ring can be rotated by pushing the notch
at the letter З (the Russian letter 'Z').
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Cryptanalysis has become an extremely complex expert-task
over the years, and tools like the Caesar Wheel shown here,
offer a good introduction into the matter.
Various other instruction tools were developed,
like the Caesar Box and several
slide-rulers.
Please note that Caesar Wheel is just a nickname for this
cipher disc. It should not be confused with the Caesar Cipher.
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© Crypto Museum. Created: Saturday 21 July 2012. Last changed: Friday, 23 February 2018 - 21:54 CET.
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