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Germany Hand Caesar Beaufort →
Polyalphabetic cipher disc · 1920-1950
The Reverse Caesar Cipher, also known as Reverse Vigenère Cipher, is
a manually operated cipher wheel, or disc, milled out of a solid piece of
brass. It is a form of the Beaufort Cipher, and
can be used as a polyalphabetic substitution cipher. The disc holds two circular
alphabets, of which the inner one is movable and in reverse order.
It also has a movable a 26-position ruler.
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The image on the right shows the cipher disc which is milled out of a solid
piece of brass. It consists of a fixed outer ring in which the 26 letters
of the Latin alphabet (A-Z) are engraved in clockwise order. The outer
ring has a milled-out area that holds the movable inner ring.
The inner ring is held in place by a bolt at the center and has the 26
letters of the Latin alphabet impressed in counter-clockwise order.
Also mounted to the bolt at the centre, is a
movable ruler that can be fixed
in any of 26 positions by means of a
knurled steel screw.
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The disc shown here is a variant of the Caesar Cipher,
of which one alphabet is in reverse order. When applied to the Hebrew
alphabet in a static manner, the reverse caesar cipher is known as Atbash [2].
In its basic form it is a simple substitution cipher, or monoalphabetic
substitution.
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A
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B
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C
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D
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E
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F
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G
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H
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I
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J
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K
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L
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M
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N
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O
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P
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Q
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R
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S
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T
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U
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V
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W
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X
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Y
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Z
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Z
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Y
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X
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W
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V
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U
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T
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S
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R
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Q
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P
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O
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N
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M
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L
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K
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J
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I
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H
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G
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F
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E
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D
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C
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B
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A
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However, as the inner disc is movable, it can be used as a polyalphabetic substitution as well.
If we align the letter 'P' of the inner disc with the 'A' of the outer disc,
the substitution is as follows:
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A
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B
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C
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D
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E
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F
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G
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H
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I
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J
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K
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L
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M
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N
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O
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P
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Q
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R
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S
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T
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U
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V
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W
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X
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Y
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Z
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P
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O
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N
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M
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L
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K
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J
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I
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H
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G
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F
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E
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D
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C
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B
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A
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Z
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Y
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X
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W
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V
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U
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T
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S
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R
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Q
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The advantage of the Reverse Caesar Cipher is that it is reciprokal (reversible),
even when the inner alphabet is shifted. As a result, the same procedure can
be used for coding and decoding.
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It is likely that the cipher disc shown above was manufactured in German,
as its rear surface is
impressed with the text LINGE Pleidelsheim.
Linge might refer to the name of the maker or a company or institute,
whilst Pleidelsheim is a village in Germany, about 30 km north of Stuttgart.
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A nearly identical sample in our collection is shown in the image on the
right. It is engraved with the text REGENSBURG Verschlüsselung.
Regensburg is another German city, about 100 km north of München, and
Verschlüsselung is the German word for encryption.
An identical one with the same inscription is held in the collection of the
Cipher History Museum (USA) [4].
A similar disc
is shown on the
German Wikipedia
[1], but it appears to be incomplete [3]. It has a makeshift bolt at
the centre, the ruler is missing and a hole is present above the letter 'A'.
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In recent years (2014-2017) several cipher discs of this design turned up
on auction sites such as eBay. Apart from small manufacturing details, these
are all nearly identical, but the inscriptions at the bottom side vary.
In addition, the packaging varies wildly, from simple cloth bags to milled-out
wooden blocks.
This could mean that it was manufactured at different locations, but might
also be an indication that it was made as a promotional gift or as part of
a school assignment.
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At present we have no further information about this cipher disc, its
manufacturer or its age. If you have any additional information, please
contact us.
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© Crypto Museum. Created: Thursday 11 September 2014. Last changed: Sunday, 01 December 2024 - 10:07 CET.
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