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Gretag TC-58
Online cipher machine - under construction

The TC-58 was an electromechanical online cipher machine, developed by Gretag AG in Regensdorf (Switzerland) in 1958, as the successor to the TC-53. It was wheel-based, just like the TC-53, but introduced automatic synchronisation of the cipher stream, making it more suitable for use on (noisy) HF communication links. It was initially developed for the Swiss Army, but was also sold to the Austrian Army, albeit without the special key production device (SPG).

The image on the right shows a typical TC-58 unit. It has 12 small windows through which the cipher wheels are visible: 4 on the left, which are the actual scramblers, and 8 on the right which control the stepping, just like on the TC-53.

Below the wheels are two rows of switches. The lower row (i.e. the black switches) are used to set the initial position of the wheels. Unlike the TC-53, where the wheels can only be stepped forward, the wheels of the TC-58 can be stepped in both directions.
  
TC-58 cipher add-on for the KFF-85

Unlike the TC-53, which was used as a separate device aside an ETK teleprinter, the TC-58 was designed to go on top of the KFF-58 teleprinter and for a complete -single- unit.

Key production unit (SPG)
When using the TC-58, the operator had to set the machine to the daily key (Grundstellung) plus an additional randomly picked message key. Due to the way in which the brain works however, such keys are hardly ever random.

For this reason, Gretag developed the SPG, a small key generator that could be mounted at the left of the front panel of the TC-58. It was secret and was only supplied to the Swiss Army.

 More information
  
Schlüsselproduktionsgerät (SPG). Click for more information.

References
  1. Walter Schmid, Der Krypto-Funk-Fernschreiber KFF-58
    October 2008.
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