HC-9

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The HC-9 cipher machine

HC-9 is the name of a mechanical rotor cipher machine developed by the Swedish company AB  Transvertex in the 1950s . It was used by the Swedish army and navy under the name KRYAPP 301 (short for Swedish : kryptografiska apparatus ; German "cryptographic apparatus" ) until the 1970s .  

history

Immediately after the Second World War , the Swede Vigo Lindstein designed the cryptographic concept of the key machine . During the war he had worked as an engineer at Ericsson , where he designed and implemented a cryptanalytic device for the automatic breaking of the German “ secret writer T52 ”. The Germans took advantage of this key - teleprinter (SFM) in particular to its diplomatic secret messages to occupied Norway and to allied Finland to encrypt. These ran over land lines in neutral Sweden. The Swede Arne Beurling (1905–1986) had already managed to decipher T52 messages in the summer of 1940 . With the help of the device built by Lindstein, this deciphering could be automated. In this way, he had proven his ability to implement cryptological concepts with the help of mechanical devices.

The HC-9 was based on the well-known M-209 , which was designed by his compatriot Boris Hagelin (1892–1983) and used by the US Army in their thousands during World War II. Lindstein knew their concept very well. He worked as a technical director in Hagelin's company, AB Cryptoteknik ( German  Kryptotechnik AG ). The letters "HC" in the device name could represent a tribute to Hagelin and stand for "Hagelin Chiffer" in Swedish or "Hagelin Cipher" in English. The number “9” fits chronologically as the ninth machine in a row after the B-21 , C-35, C-36, C-37, C-38, M-209, C-442 and C-52 from the Hagelin house.

One goal was to develop a relatively simple, i.e. easy-to-use and as compact as possible machine for field use. The areas of application were not general staffs and information of strategic importance, but the lowest levels of military command , such as platoon , company and battalion . Another, namely cryptographic, goal was not to achieve “unbreakability” (which is difficult to achieve anyway), but “only” sufficient “tenacity” against cryptanalytic attacks. Both goals were achieved satisfactorily by Lindstein introducing both constructive and cryptological innovations.

construction

The external dimensions (L × W × H) of the handy machine are around 150 mm × 180 mm × 70 mm. It operates using a small hand lever on the left side and does not require electricity. Each plain text letter is individually encrypted. The machine is involutive , i.e. encryption and decryption are identical. In a viewing window at the front, alternating alphabets appear for each letter , which are used for encryption and decryption. This is done by reading the corresponding letter. The machine does not have a printer.

From a cryptological point of view, the machine consists of two partial keys , the day key and the message key . The daily key is implemented on the one hand using a small paper punch card . This is inserted into the back of the machine and can be easily changed. The second component of the daily key consists of a sheet of paper. It is printed line by line with sixteen " randomly scrambled " alphabets. It can be changed just as easily, which happens once a day. It is also placed in the machine. This method protects the operator from setting errors and avoids the need to check the correctness of the set day key by test encryption of a control text, which is necessary on similar machines (such as the CD-57 , which works with reversible pens).

The slogan key is selected and set individually for each individual message. There are five setting wheels for this purpose. Each can be manually set to one of the 26 letters of the Latin alphabet . There are 26 5 or 11,881,376 possibilities for this.

literature

  • Bengt Beckman: Arne Beurling and Hitler's secret writer. Swedish deciphering successes in WWII. Springer, Berlin et al. 2005, ISBN 3-540-23720-8 .
  • CA Deavours and Louis Kruh: The Swedish HC-9 Ciphering Machine. Cryptologia, 13: 3, 1989, pp. 251-265, doi: 10.1080 / 0161118991863943 .

Web links

Commons : HC-9  - collection of pictures, videos and audio files

Individual evidence

  1. ↑ CA Deavours and Louis Kruh: The Swedish HC-9 ciphering machine. Cryptologia, 13: 3, 1989, p. 252.
  2. ↑ Transvertex HC-9 Cipher Machine at CipherMachines.com (English), accessed on August 26, 2019.