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Switzerland
Gretag
Omnisec
  
Gretacoder 906
Portable off-line electronic cipher machine - wanted item

Gretacoder 906, also known as GC-906, is a portable electronic cipher machine, introduced in 1980 by Gretag AG in Regensdorf (Switzerland) as the successor to the GC-905. Contrary to the GC-905, it features a full keyboard and an LCD display. It is compatible with the earlier GC-805.

The predecessor of the device, Gretacoder 905, had been introduced in 1977, and was one of the first electronic pocket cipher machines in the world. It came at a time when competitor Crypto AG (Hagelin) had just released its first electronic cipher machine, the H-460. A few years earlier, Crypto AG had secretly been taken over by the American intelligence service CIA and its German counterpart, the BND. Although the Gretacoder 905 was less user-friendly than Hagelin's H-460, it was smaller and could be carried in a pocket.

Unknown to the public however, the Hagelin H-460 contained an NSA-created backdoor, which allowed CIA and BND to read the diplomatic traf­fic of a number of countries [1]. Losing custo­mers to Gretag meant that they would no longer be able to do that, so it was decided to let Hage­lin also introduce a pocket cipher machine, but one that was more user-friendly than the Greta­coder 905 and would be preferred by customers.
  

Hagelin's answer to the Gretacoder 905 was the HC-520. It had the size of a pocket calculator of the era and had an alphanumeric keyboard and and a Liquid Crystal Display (LCD). In reality, the HC-520 had been developed by Siemens and contained an NSA-developed backdoor. As it made the Gretacoder 905 less popular, Gretag decided to develop a new pocket cipher machine as its successor: the Gretacoder 906. It was approximately the same size and was introduced in 1980.

The Gretacoder 906 was not compatible with its predecessor, Gre­ta­coder 905, but with Gre­ta­co­der 805 — a family of modular electronic cipher machines that had been introduced in 1978. It allowed Gretag's users to choose between com­patible desktop, briefcase and pocket devices.

To make Gretacoder 906 even more attractive, Gretag introduced the PE-906 peripheral expansion unit shown in the image on the right. It contains a thermal printer, a punched paper tape reader and an acoustic modem. At the front of the PE-906 is a cradle for the Gretacoder 906.

The image on the right shows how the PE-906 combination could be used in a hotel room. The Gretacoder 906 is installed in the cradle at the front. The acoustic coupler allows encrypted text to be sent and received via any regular analog telephone line (POTS), using any telephone set.
  

Gretacoder 906 was introduced in 1980 and was in production for many years. In 1987, as part of a reorganisation, the production rights were transferred to Omnisec, another Swiss crypto manufacturer, founded that same year by former Gretag employee Dr. Pierre Schmid. It has since come to light however, that Omnisec was owned by the CIA, just like competitor Crypto AG [2].

PE-906 - left angle view
Thermal paper compartment
Manual tape reader
Acoustic coupler fitted to the handset of a telephone
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PE-906 - left angle view
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Thermal paper compartment
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Manual tape reader
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Acoustic coupler fitted to the handset of a telephone

Compatible devices
GC-505
Portable versionn of the Gretacoder 805 encryption device
Desktop version of the Gretacoder 805 encryption device
Gretacoder 521 for Haslter SP-300 teleprinter
Provenance
At present, we do not have a Gretacoder 906 in our collection, but we do have the PE-906 peri­pheral expansion unit shown above. It was found in 2024 in Peru. Although the device was deve­loped by Gretagthe motherboard carries the name Gretag — it was marketed by Omnisec after they had taken over much of the Gretag portfolio. This suggests that the Peruvian government was one of Omnisec's customers, and perhaps also a former customer of Gretag.

From the date codes on the various parts inside the device, it seems likely that it was produced in 1987, the year in which Omnisec took over production and distribution from Gretag. As it has mean­while become known that Omnisec was owned by the American Central Intelligence Agency (CIA), it is possible (but not certain) that the Cretacoder 906 contains a so-called backdoor.


Parts
Gretacoder 906
Peripheral PE-906
Acoustic modem
Gretacoder 906   GC-906
The central piece is the Gretacoder 906 (GC906) device itself. It is similar in size to its precessor, Gretacoder 905, but has a full keyboard and an 11-character Liquid Crystal Display (LCD).

The device is built around the efficient low-power CDP1802 microprocessor, developed by RCA in the mid-1970s. It is powered by internal batteries, by an external AC power adapter or by the PE-906 peripheral expansion unit.

  

Peripheral   PE-906
Although it is possible to use the Gretacoder 906 as a stand-alone device, it could be expanded with several interfaces, by placing it in the PE-906 peripheral adapter shown on the right. The GC-906 connects to it via 25-pin connector.

The PE-906 provides power, additional memory for 4000 characters, a hand-operated punched paper tape reader, a thermal printer and an acoustic modem that allows encrypted messages to be transmitted and received via any standard analogue telephone set.

  

Acoustic coupler
The PE-906 was supplied with the acoustic coupler shown on the right, which consists of two rubber cups with a microphone and speaker respectively. It has an 8-pin DIN plug that mates with a DIN socket at the left side of the PE-906.

The rubber caps can be placed over the mouth and ear piece of the handset of a standard ana­logue telephone. Together with the built-in modem of the PE-906, it allows encrypted mes­sages to be sent and received as a series of audible tones.

  

PE-906 - right angle view
PE-906 - left angle view
Thermal paper compartment
Manual tape reader
Connection between the GC-906 and the PE-906
Cradle lifted
DIP switches under the cradle
8-pin DIN socket for connection of the acoustic coupler
Acoustic coupler
Connecting the acoustic coupler
Acoustic coupler connected to the PE-906
Acoustic coupler fitted to the handset of a telephone
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×
B
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PE-906 - right angle view
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PE-906 - left angle view
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Thermal paper compartment
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Manual tape reader
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Connection between the GC-906 and the PE-906
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Cradle lifted
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DIP switches under the cradle
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8-pin DIN socket for connection of the acoustic coupler
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Acoustic coupler
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Connecting the acoustic coupler
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Acoustic coupler connected to the PE-906
B
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Acoustic coupler fitted to the handset of a telephone

Interior
GC-906
At present we are unable to show the interior of the Gretacoder 906, as we don't have one of these in our collection. If you know of a Gretacoder 906 that is available, please contact us.





PE-906
The PE-906 peripheral expander is housed in a metal enclosure that measures 315 × 210 × 70 mm and weight 2675 grams. It consists of a base panel that holds the main printed circuit board (PCB), and a molded case shell that covers the base panel and holds the manual optical paper tape reader. The interior can be accessed by loosening 4 bolts in the corners of the bottom panel.

After taking off the case shell, the main PCB is revealed as shown in the image on the right. The PCB is roughly devided into three sections: the power supply unit (PSU) at the rear, the printer at the centre, and the logic circuits at the front.

The logic circuits are based on the COSMAC CDP1802 microprocessor family, pioneered by RCA in the mid-1970s. The main board holds a CDP1851 I/O Interface, a CDP1854 UART (serial port), two CDP1856 data bus buffers, 6KB of CMOS RAM (HM6116), two 2732 EPROMs with firmware, and a dedicated AM7910 modem chip.
  

The CDP1802 processor itself is not present. It is possible that it was removed from the empty socket on the PCB, or that the PE-906 is connected directly to the databus of the CDP1802 pro­cessor inside the Gretacoder 906 itself. Any further information on this topic is most welcome.

Interior and inside of the case shell
Interior
RAMs and EPROMs
Modem, UART and I/O expander
Thermal printer
Power Supply Unit
Main PCB - top view
Optical tape reader
C
×
C
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Interior and inside of the case shell
C
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Interior
C
3 / 8
RAMs and EPROMs
C
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Modem, UART and I/O expander
C
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Thermal printer
C
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Power Supply Unit
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Main PCB - top view
C
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Optical tape reader

Specifications
  • Device
    Pocket cipher machine
  • Purpose
    Text encryption
  • Manufacturer
    Gretag, Omnisec
  • Type
    Gretacoder 906
  • Model
    GC-906
  • Year
    1980
  • Compatibility
    see below
  • Algorithm
    Prioprietary non-linear
  • Keys
    Primary key: 16 characters 1
    Secondary key held in PROM plug-in unit
    Modifier key (message key) 10 characters randomly generated
  • Key space
    ~ 1060
  • Key period
    1053
  • Keyboard
    28 keys (9 control keys)
  • Formatting
    5-letter groups (A-P)
  • Editing
    Character shift/insert/delete, Block shift
  • Memory
    719 characters
  • Display
    11-character LCD 5 × 7 matrix plus 7 control indicators
  • Temperature
    0°C to +50°C
  • Storage
    -15°C to +70°C
  • Dimensions
    185 × 130 × 26 mm
  • Weight
    550 g
Peripheral   PE-906
  • Device
    Peripheral expander for Gretacoder 906
  • Manufactuers
    Gretag, Omnisec
  • Model
    PE-906
  • Peripherals
    Thermal printer
    Acoustic modem
    Extended memory
    Manual paper tape reader
    Mains PSU
  • Memory
    4000 characters
  • Dimensions
    315 × 210 × 70 mm
  • Weight
    2675 g
Compatibility
Connections
Acoustic coupler
The acoustic coupler is connected to the 8-pin 270° DIN socket at the left side of the PE-906. The image below shows the pinput of this connector, when showing into the socket. The wiring is currently unknown.

  1. ?
  2. ?
  3. ?
  4. ?
  5. ?
  6. ?
  7. ?
  8. ?
Gretacoder socket
Inside the cradle of the PE-906 — in which the Gretacoder 906 can be installed — is a 25-pin male receptacle that mates with the 25-pin female connector at the rear of the Gretacoder 906. The diagram below shows the pinout of the PE-906 receptacle when looking into the cradle. The wiring is currently unknown.

  1. ?
  2. ?
  3. ?
  4. ?
  5. ?
  6. ?
  7. ?
  8. ?
  9. ?
  10. ?
  11. ?
  12. ?
  13. ?
  14. ?
  15. ?
  16. ?
  17. ?
  18. ?
  19. ?
  20. ?
  21. ?
  22. ?
  23. ?
  24. ?
  25. ?
    DB25 male connector inside the cradle of the PE-906
Datasheets
  1. CDP1802 CMOS 8-Bit Microprocessor
    1305.2. Intersil, March 1997 (1999).

  2. CDP1851 CMOS Programmable I/O Interface
    1056.2. Intersil, March 1997 (2002).

  3. CDP1854 CMOS UART
    1715.2. Intersil, March 1997 (2002).

  4. CDP1856 4-Bit Bus Buffers/Separators
    Undated.

  5. CDP1868, CMOS 4-Biy Latch and Decoder Memory Interface
    Undated.

  6. AM7910 World-Chip FSK Modem
    04262. AMD, June 1989. Rev. D.

  7. HM6116 2048 × 8-bit High Speed CMOS Static RAM
    Hitachi. Undated.
Documentation
  1. Gretacoder 805, Modular High Security Off-Line Encryption System
    Full-colour 6-pages sales brochure.
    Gretag Limited, May 1984.
References
  1. Paul Reuvers and Marc Simons, Operation RUBICON
    Crypto Museum, 19 March 2020.

  2. Rundschau, Die Geheimdienst-Affaire weitet sich aus
    SRF Television (Switzerland). 25 November 2020.

  3. Wikipedia, RCA 1802
    Visited 23 January 2024.
Further information
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Crypto Museum. Created: Saturday 13 January 2024. Last changed: Wednesday, 31 January 2024 - 14:34 CET.
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