The HC-9 was a mechanical cipher device manufactured by the Swedish company AB Transvertex. It was designed in the early 1950's for the Swedish Armed Forces and likely remained in use up to the 1970s. This machine was used for low-level communications such as platoon, company, up to battalion levels and in regimental and brigade staffs.The machine dimensions are 18 x 15 x 7 cm.
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- Photograph of an HC-9
- Another HC-9 photograph with a description
- A description of the machine and a simulator in QBASIC
- Discussion of the machine's operation
- Cipher A. Deavours and Louis Kruh, The Swedish HC-9 Ciphering Machine, Cryptologia, Vol. 13(3), July 1989, pp. 251–265
- Cipher A. Deavours and Louis Kruh, The Swedish HC-9 Ciphering Machine Challenge, Cryptologia, Vol. 14(2), April 1990, pp. 139–144
- H. P. Greenough, Cryptanalysis of the Swedish HC-9: A Known-Plaintext Approach, Cryptologia, 1997, 21(4), pp353–367.