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Gretag Telex
Electronic telex encryptor
- this page is a stub
TeleCrypto 812, abbreviated TC-812, also known as Gretacoder 812,
was an electronic encryption/decryption device
for on-line and off-line
telegraph traffic (telex) over short wave (HF)
radio links and wired teleprinter circuits, introduced in 1971 by
Gretag AG in Regensdorf (Switzerland).
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The device is housed in a 3U 19" rackmountable enclosure, and was usually
supplied in a watertight green aluminium container, as shown in the image
on the right. It is powered from the AC mains and provides power and line
circuits for the connected
Siemens T-100 teleprinter.
The device uses three different cryptographic key types:
(1) secretly wired patch cords in a locked and removable key unit,
(2) a secret 10-character elementary key that is entered on the keyboard
of the connected teleprinter,
and (3) a non-scret automatically generated auxiliary key.
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The auxiliary key can be seen as a message key and is different for each
transmitted message. This allows the same daily key (i.e. the patch cords
and the elementary key) to be the same for all messages on a given day,
without compromising cipher security. According to the brochure [B],
the system resists Kerckhoffs' superimposition [1] and
Friedman's
Index of Conidence [2].
The TC-812 was introduced in 1971 and was in production until at least
1979. It was used by the Swiss Army and by several other countries,
including Austria. It must have been a cryptographically strong machine,
as it is known from Operation Rubicon that
Gretag machines were unbreakable
for the American National Security Agency (NSA)
and the German
Zentralstelle für das Chiffrierwesen (ZfCh) [3].
The device can be seen as a direct competitor of the
Hagelin T-450,
which was available in the same era, but which contained a
backdoor that had been inserted by the NSA.
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Device Electronic telex encryptor Purpose On-line and off-line telex encryption Model TC-812 Name Gretacoder 812, TeleCrypto 812 Manufacturer Gretag AG Years 1971-1979 Country Switzerland Algorithm Proprietary Alphabet ITA-2 (CCITT Code No. 2) Speed 45.45, 50, 75, 100 baud 1 Line Single current 60/120 V, 20/40/60 mA
Double current ±60 V, 20/40/60 mA Power 110/220 V AC +15%/-20%, 50/60 Hz ±10% Consumption 100 W (without teleprinter) Backup NiCd battery (1 hour backup) Temperature 0°C to +50°C Storage -20°C to +70°C Dimensions 280 × 535 × 355 mm (HWD) 2 Weight 25 kg
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The baudrate is set internally.
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Weight including watertight transport container.
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Secret wiring Key unit, pluggable wires: ~ 1023 Secret elementary key 10 letters typed on keyboard: ~ 1014 Non-scret auxiliary key 8 letters, auto-generated
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- Automatic synchronisation
- Automatic re-synchronisation
- Automatic propagation delay correction (adaptive, fixed)
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© Crypto Museum. Created: Thursday 28 August 2025. Last changed: Thursday, 02 October 2025 - 13:33 CET.
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