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Transpositeur
Alphabet transposition cipher · 1912

Le Transpositeur à permutation secrètes (secret transposition cipher), commonly abbreviated to Transpositeur, was a manual cryptographic device, developed around 1912 by Société des Codes Télégraphiques Georges Lugagne in Paris (France), and manufactured by the famous slide rule manufacturer BARBOTHEU, also in Paris [4]. The device was succeeded in 1930 by Le Sphinx.

The device measures 102 x 192 x 17 mm and weights approx. 300 grams. It is made of wood and has 10 milled-out gutters in which 20 rulers can be moved in pairs. The bottom is enforced with an aluminium panel which also adds weight.

The rulers have an ivory layer at the top, in which the 20 alphabets are engraved in black. Each ruler is marked with a red number from 0 to 9. The upper 10 alphabets have their number at the top, whilst the lower alphabets have it at the bottom. Two transparent windows are used to read the plain text and cipher text letters.
  
Transpositeur in use

The design was covered by patents FR 461,217 and GB 23,204, both filed by Georges Lugagne. When unused, the device is stored in a purpose made storage box with dark red velvet lining. The storage case is made of wood and is covered with black bookbinding linen, that also acts as the rear hinge. At the front edge the name of the manufacturer, BARBOTHEU, is impressed in golden letters. When closed, the case is locked by a metal rod that is pushed-in from the front right.

Storage case Opening the storage case Transpositeur inside storage case Transpositeur The name of the manufacturer imprinted in gold in the edge of the storage case Transpositeur Top view Transpositeur in use
Plain text One set of rules removed from the carrier Close-up of a set of rules Close-up of a single slide rule Serial number Side view Slider detail Bottom side
A
×
A
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Storage case
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Opening the storage case
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Transpositeur inside storage case
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Transpositeur
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The name of the manufacturer imprinted in gold in the edge of the storage case
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Transpositeur
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Top view
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Transpositeur in use
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Plain text
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One set of rules removed from the carrier
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Close-up of a set of rules
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Close-up of a single slide rule
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Serial number
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Side view
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Slider detail
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Bottom side

Features
The diagram below shows how the Transpositeur was used for coding and decoding messages. The operator would first set the pre-arranged daily key, by placing the rulers in the proper order. Note that the upper rulers can be scrambled independently from the lower ones. Messages were coded 10 characters at a time. In the example below, the message ATTACKNOW is being read.


The device consists of a wooden frame from which 10 gutters have been milled-out in such a way that each one can hold two alphabet rulers: an upper one and a lower one. The actual sliders, or rods, are constructed in such a way that they slide smoothly through the gutters without binding or falling out. Two transparent windows – with two black hairlines each – are mounted to the frame at fixed positions. They mark the position of plain text and cipher text (or vice versa).
Permutations
The device has 20 sliding alphabet rulers, 10 of which can be identified as the upper alphabets, whilst the other 10 are the lower alphabets.This gives 10! (or 3,628,800) possible combinations 1 of alphabets for the upper half only. As the same is true for the lower 10 alphabets, the total number of combinations is 3,628,800 x 3,628,800, which is no less than:

13,168,189,440,000

Note that this result is only limited because the upper and lower alphabets can not be mixed. This limitation was lifted in 1931 by Lugagne's employee Paul Godillon, resulting in the successor of the Transpositeur – Le Sphinx – with a fenomenal 2,432,902,008,176,640,000 combinations.

  1. 10! (10 factorial) is the mathematical notation for 10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1

Operation
Before exchanging a message by means of the Transpositeur, both parties first have to agree which alphabet is used in each position. This is done by quoting the red numbers that are printed at the end of each rod. This is known as the settings, or the key, and is usually pre-arranged between the parties. For the default position, which we have used on this page, the key would be:

1 2 3 4 5 6 7 8 9 0
1 2 3 4 5 6 7 8 9 0

Both users should now install the upper and lower alphabets in the order given by the pre-arranged key. For the above one, the setup would be idential to the storage position:

Default setup. Click to enlarge.

The Transpositeur is constructed in such a way that the user can slide the rulers up and down manually. There are two windows through which we can read a row of letters. Now slide the rulers in such a way that the first 10 letters of the plaintext are visible in the upper window, e.g.:

TOPSECRETS

All you now have to do is read the ciphertext from the lower window, which in this case is:

RERPIBDOWB

All the receiving party has to do, is slide the rulers so that the ciphertext is visible in the lower window. The original plaintext can now be read from the upper window.

Top view Transpositeur in storage position Transpositeur in use Plain text Cipher text
B
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B
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Top view
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Transpositeur in storage position
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Transpositeur in use
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Plain text
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Cipher text

Cipher security
Despite the large number of possible arrangements of the alphabets, Le Sphinx provides only low-grade cipher security. This is mainly caused by the fact that the arrangment of the alphabets does not change during the course of a message. If a message is long enough, it can be solved by frequency analysis. For very short messages, the cipher would be relatively secure though.

Another weakness of the system is that there is no provision for sending the key at the start of a message. Instead, it has to be pre-arranged. This was also the case with the German Enigma cipher machine, although in that case, procedures were in place to add a random message key.


Alphabets
The table below shows each of the 20 scrambled alphabets of our device. Note that all alphabets are in a differently scrambled order. Also note that the upper alphabets can not be mixed with the lower alphabets. This can be seen as a cryptographic weakness, as it significantly reduces the number of combinations. This problem was solved in 1930, in improved device Le Sphinx.

1 JKYLMNAPQRESTVIWXZOBCDUFGH
2 WXAZBCEDFGIHJKOLMNUPQRYSTV
3 BCODFGUHJKYLMNAPQRESTVIWXZ
4 PQIRSTOVWXUZBCYDFGAHJKELMN
5 FGUHJKYLMNAPQRESTVIWXZOBCD
6 ZBECDFIGHJOKLMUNPQYRSTAVWX
7 CDOFGHUJKLYMNPAQRSETVWIXZB
8 RSATVWEXZBICDFOGHJUKLMYNPQ
9 HJIKLMONPQURSTYVWXAZBCEDFG
0 MNEPQRISTVOWXZUBCDYFGHAJKL
1 GHEJKLIMNPOQRSUTVWYXZBACDF
2 QRUSTVYWXZABCDEFGHIJKLOMNP
3 DFAGHJEKLMINPQORSTUVWXYZBC
4 LMENPQIRSTOVWXUZBCYDFGAHJK
5 STYVWXAZBCEDFGIHJKOLMNUPQR
6 XZUBCDYFGHAJKLEMNPIQRSOTVW
7 NPAQRSETVWIXZBOCDFUGHJYKLM
8 VWIXZBOCDFUGHJYKKMANPQERST
9 KLYMNPAQRSETVWIXZBOCDFUGHJ
0 TVOWXZUBCDYFGHAJKLENMPIQRS

 
Successor
Around 1930, the Transpositeur was succeeded by the similar but improved device known as Le Sphinx. Like the Transpositeur it had 10 double sliding alphabets, but these could be mixed.

Le Sphinx was made of aluminium rather than wood, and came in a stylish bakelite storage case. Both devices are extremely rare.

 More information
  
Le Sphinx manual cipher system

References
  1. Georges Lugagne, French Patent 461.217
    Filed 24 October 1913, granted 23 December 1913. Priority date 23 October 1912.

  2. Georges Lugagne, British Patent 23,204
    Filed 14 October 1913, granted 9 April 1914.

  3. Linialis, Règles Rares ou Originales
    Website Linealis.org. Retrieved April 2016.

  4. Daniel Tant, Le transpositeur à permutations secrètes
    Date unknown. Retrieved April 2016 (French). 1
  1. Reproduced here by kind permission of the president of the
    Association des Réservistes du Chiffre et de la Sécurité de l'Information.

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Crypto Museum. Created: Thursday 20 July 2017. Last changed: Monday, 24 July 2017 - 19:41 CET.
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