Click for homepage
← Switzerland
Hand
  
Swiss Réglette
Transposition slide rule

Réglette 1 was a manual polyalphabetic transposition cipher – or shift cipher – in the shape of a slide rule, developed around 1918 by the Nachrichtensektion (Intelligence Section) of the Swiss Army. It is based on the Vigenere Cipher, and was used by the Swiss Army up to Brigade level [2].

The device measures 208 × 30 × 5 mm and weights 92 grams. It consist of three 1 cm-wide metal rules, of which the outer two act as a frame in which the middle one is movable.

The fixed (outer) rules hold the numbers 00-99, with the odd number on the left and the even ones on the right. The movable centre piece, holds the 26 letters of the Latin alphabet, the numbers 0-9 and some punctuation characters. Also present on the slider are the most common bigrams for the German language, such as 'de', 'ch' and 'st', plus a swap character; 50 in total.
  
Swiss Réglette slide rule strip cipher with leather wallet

A second slider (identical to the one at the centre) is stowed at the rear. It should be chained to the existing slider, to allow wrapping of the alphabet. The device was in used until 1939, after which it was deemed insecure by Dr. Hadwiger [2]. A simplified version of Réglette – for training purposes – was introduced in 1949, under the name Chiffrierschieber Cäsar (cipher slide Caesar). To avoid confusion with other Caesar-based hand ciphers, we have named that one Swiss Caesar.

  1. Réglette – sometimes written as Reglette – is the French word for Ruler. In this context it means Slide Rule.

Swiss Réglette in leather wallet Swiss Réglette slide rule strip cipher with leather wallet Swiss Réglette with leather wallet and additional slider Additional slider stowed at the rear Shifted center part of the slide rule Size of the slide rule compared to a hand Swiss Réglette strip cipher in its leather wallet Serial number (21)
A
×
A
1 / 8
Swiss Réglette in leather wallet
A
2 / 8
Swiss Réglette slide rule strip cipher with leather wallet
A
3 / 8
Swiss Réglette with leather wallet and additional slider
A
4 / 8
Additional slider stowed at the rear
A
5 / 8
Shifted center part of the slide rule
A
6 / 8
Size of the slide rule compared to a hand
A
7 / 8
Swiss Réglette strip cipher in its leather wallet
A
8 / 8
Serial number (21)

Operation
For encryption of messages, a cryptographic KEY is needed – consisting of a Keyword and a two-digit Key Number – that has to be known by the recipient. In case of (war) mobilisation, suitable KEYs would be issued by the General Staff Department of the Army [2]. An example of a KEY is:

DREHZAHL 37

Shift the slider, so that the first letter of the Keyword (D) lines up with the Key Number (37). Now find the first character of the plain text on the slider, and write down the number next to it. Now move the slider so the the second letter of the Keyword lines up with the Key Number. Find the second letter of the plain text and write down the number next to it. As soon as all letters of the Keyword are used, continue with the first letter of the Keyword, until the message is complete.

For long messages – consisting of more than 15 to 20 words – it is recommended to split it into several parts, using the swap character ( i.e. the hatched field) to indicate the start of the next part. For each part, a new Key Number should be used (subject to the issued KEY instructions).

DREHZAHL 37 51 00 92 78

Once the message is complete, the cipher text – consisting of 2-digit numbers – must be written out in groups of 5 digits each. If the last group is partly unused, it should be padded with random digits. The message is now ready for transmission via radio (morse-code), letter or telegram. At the receiving end, the message can be decrypted by using the above procedure in reverse order.


References
  1. Günter Hütter, Information about Réglette
    Personal correspondence, September 2017.

  2. Rudolf J. Ritter, Das Fernmeldematerial der Scheizerischen Armee seit 1875, 10. Folge
    Communications equipment of the Swiss Army since 1875, Volume 10 (German).
    Bern (Switzerland), Autumn 2002. pp. 23-25.
Further information
Any links shown in red are currently unavailable. If you like the information on this website, why not make a donation?
© Crypto Museum. Created: Sunday 03 September 2017. Last changed: Sunday, 23 February 2020 - 18:19 CET.
Click for homepage