Sigaba

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The American key machine Sigaba

The Sigaba (spelling: SIGABA ; from the German side also called AM-2 for "American Machine No. 2") is a key rotor machine that was used in communications by the US military during World War II . The Sigaba, also short ECM (for Electric Cipher Machine , German: "Electric key machine ") or more precisely ECM Mark II called, was also called Converter M-134-C by the US Army and as CSP-889 by the US Navy and - in a modified form - referred to as CSP-2900 . In contrast to the German key machine Enigma , which is based on similar principles, encrypted radio messages could not be deciphered ("cracked") with the Sigaba .

history

The Sigaba key machine is based on the principle of using rotors (rollers) for the purpose of encrypting texts, as invented and patented by the American Edward Hugh Hebern (1869–1952) in 1917 . These principles were refined under the direction of the American cryptologist William Frederick Friedman, particularly with regard to an irregular rotation of the rotors, and thus cryptographically significantly strengthened. His colleague Frank Rowlett came up with the idea of ​​using additional rollers for the irregular switching of the encryption rollers. The M-134, then the M-134-A, called SIGMYC, and finally the M-134-C Sigaba in 1936 were created in quick succession as precursors.

The Sigaba is described in U.S. Patent 6175625, filed in 1944 but not published until 2001

function

Sigaba

Similar to the German key machine Enigma, the Sigaba also uses several rollers with which the letters of the plain text to be encrypted are permuted several times and ultimately result in the ciphertext . Unlike the Enigma, which only used three or a maximum of four rollers, the Sigaba used a total of fifteen rollers. Furthermore, the Sigaba avoided the main cryptographic weakness of the Enigma, namely the reverse cylinder . A toggle button located to the right of the rollers is used to selectively set the encryption or decryption mode.

The fifteen rollers of the Sigaba are divided into three roller sets, each with five rotatable rollers. Only one set of rollers, the cipher rotor bank , consisting of the five cipher rollers, actually encrypts the text, while the other two sets of rollers, the control rotor bank and the index rotor bank (German: "index roller set") are only used to control and generate as irregular a progression of the cipher rollers as possible.

  • The five cipher rotors have 26 electrical contacts on both sides for the 26 capital letters of the Latin alphabet , which are (at that time) secretly connected in pairs by 26 isolated wires inside the cylinder. The current entering the roller from one side via a contact plate leaves it again on the other side via another contact plate. In this way, the desired permutation (exchange of characters) for encrypting a letter is achieved.
  • The five control rotors also have 26 electrical contacts on both sides, which are also labeled with the 26 letters of the alphabet. Unlike the cipher rollers, however, the control rollers receive four signals, which are split into ten groups of one to six wires after the set of control rollers has passed through.
  • The third and last roller set consists of five index rotors , which are significantly smaller than the cipher rollers and control rollers and only have ten contacts on each side. The contacts of the index rollers are not labeled with letters, but have numbers, starting from 10 to 19 for the first index roller up to 50 to 59 for the fifth index roller. In contrast to the other ten reels, the index reels do not move during encryption. Their output signals control the progression of the encryption rollers in an irregular manner.
The set of rollers

Due to the irregular roller progression and the neither involutor nor fixed point-free permutations that the roller set causes, the Sigaba is cryptographically much stronger than the German key machine Enigma and, in contrast to it, could never be broken.

With the help of an adapter, called CSP 1600, which replaced the usual set of rollers with a special one, the Sigaba could be converted into a Combined Cipher Machine , which was used for the secret exchange of messages with the British allies .

literature

  • Friedrich L. Bauer : Deciphered Secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin et al. 2000, ISBN 3-540-67931-6 .
  • Michael Lee, Cryptanalysis of the Sigaba. Dissertation, University of California, Santa Barbara CA 2003 ( PDF; 0.7 MB ).
  • Klaus Schmeh : Code breakers versus code makers. The fascinating story of encryption. 2nd Edition. W3L-Verlag, Herdecke et al. 2008, ISBN 978-3-937137-89-6 .
  • John JG Savard, Richard S. Pekelney: The ECM Mark II. Design, History and Cryptology . In: Cryptologia. 23, 3, July 1999, ISSN  0161-1194 , pp. 211-228.

Web links

Commons : Sigaba  - album with pictures, videos and audio files

Individual evidence

  1. ↑ Friedrich L. Bauer: Deciphered secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin et al. 2000, p. 117.
  2. ↑ Patent US1510441 . ‌
  3. ↑ Patent US6175625 . ‌