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Gretacoder 805
Electronic off-line cryptographic system

The Gretacoder 805 was a flexible off-line cryptographic system developed and built by Gretag (later: Gretacoder Data Systems) in Regensdorf (Switzerland) in the late 1970s. It was one of the first fully electronic microprocessor-based cipher machines. Due to its modular design, different configurations of the Gretacoder 805 exist, ranging from large desktop systems (complete with a large page printer, paper tape reader and tape puncher) to small portable suitcase systems [1].

The image on the right shows the portable version of the Gretacoder 805 with its typical bright yellow colour. It is microprocessor-based and has a ptext memory of 4000 characters, a high quality keyboard and a smooth-scrolling 37-character alpha-numerical plasma display.

To the right of the display is a small plastic plug-in unit that was used as secundary cryptographic key. To the left of the keyboard is a narrow box with a built-in thermal column printer covered by a metal lid. It allows a hard copy to be made on 60 mm wide paper.
Portable version of the Gretacoder 805

The entire unit fits nicely inside a standard slim-line samsonite briefcase, and was powered directly by the (230V) mains. The Gretacoder 805 has a modular design. The thermal printer at the left can be removed by releasing two bolts and can be replaced by other peripherals, such as a telex interface, an acoustic coupler (modem) or an empty storage box.

The portable Gretacoder 805 was a direct competitor to the Hagelin HC-530 that had a similar appearance. The 805 is a very rare item of which only of few suitcase versions (shown here) have survived. The desktop version has been rediscovered in 2012 and as far as we currently know, it is the only one that has survived. Although the Gretcoder 805 was a very popular cipher machine in the late 1970s and the early 1980s, we don't know how many units were eventually sold.

The Gretacoder 805 inside a standard Samsonite briefcase Portable version of the Gretacoder 805 Gretacoder 805 main unit Front view of the main unit Close-up of the electronic key block The lid of the printer The thermal printer of the Gretacoder 805 The thermal printer of the Gretacoder 805

The microprocessor-based Gretacoder 805 has a full QWERTY keyboard for message input. Output is via the 37-character smooth scrolling plasma display or through an external printer. Upgrade kits, consisting of a replacement keyboard and a set of EPROMs, were available for other languages such as Arabic. An example of the latter is shown in the full-colour brochure [2]. The unit is turned on with the green button at the top left of the keyboard, as shown in this image:

After switching the unit on with the large green switch at the top left of the keyboard, the mode of operation can be selected with the top row of keys on the keyboard. Most of these keys have two functions: the character that is printed on the key-top, and the function (MODE) that is printed above the key. Below is a close-up of the top row. Click for a larger view.

Main unit
The main unit of the desktop station is identical to that of the desktop version, except for the colour of its body. It is basically a small computer in a single case, consisting of a motherboard, a keyboard, a plasma display, a slot for the secundary key, and a built-in Power Supply Unit (PSU).

The image on the right show a GC 805 main unit it is typical bright yellow colour. It was also available in a neutral grey tone. The unit has a fixed power cable that connects directly to the mains. At the left side is a large 50-pin D-type socket for the connection of a peripheral, such as the small thermal printer shown on this page.

The main unit is designed to fit nicely inside a standard Samsonite briefcase of the late 1970s, together with one peripheral. In our case the space on the left is taken by the printer, but it was also possible to use an acoustic modem.
Gretacoder 805 main unit

The full range of available options is shown below. At the rear of the main unit is a large connector that can be used to connect to an external page printer and/or a papertape reader/puncher. This connector is intended for the desktop version and is not used here.

The image on the right shows the main unit in operation. After switching the unit on, the unit performs a selftest and shows that the primary key has not been stored.

At present we have no further information about the operation of the Gretacoder 805 as we do not have a user manual. You can help us by providing additional information. Ultimately, we would like to bring the unit back to life again.
Gretacoder 805 in operation

Gretacoder 805 main unit Connector at the left side of the main unit Connector at the rear of the main unit Secret key module Gretacoder 805 in operation Example of a text

Column printer
For portable use, a small thermal printer was available. It is housed in a narrow sloped case that fits nicely to the left side of the main unit, connecting directly to the 50-way D-type socket. The printer can be used to print the ciphertext or the decrypted plaintext.

The image on the right shows a typical thermal column printer as it is present in the portable Gretacoder 805 shown here. It takes grey 6 cm wide paper rolls that were commonly used in calculators and cash registers in the late 1970s.

The ciphertext is printed in two 5-letter groups per line. Once printed, the ciphertext could be sent to the recipient by regular mail, by courier or by any other means of transmission. When the top lid of the printer is closed, a thin metal strip ensures that the output from the printer does not re-enter the printing mechanism.
Small thermal printer (open)

Towards the rear of the printer is a small storage compartment with spare fuses. It can also be used to store the mains plug before closing the case, which is necessary as there is no other space in the slim-line briefcase. The images below show how the mains plug should be stored.

Small thermal printer (closed) Small thermal printer (open) Small storage compartment Opening the storage compartment Placing the mains plug inside the storage compartment The mains plug stored inside the storage compartment The printer mounted to the left side of the main unit The printer mounted to the left side of the main unit (closed)

Cryptographic keys
The cryptographic key of the Gretacoder 805 is made up of three individual components: a 16-character alpha-numerical string that is entered on the keyboard (primary key), a fixed secundary key that is stored in a plug-in module (crypto ignition key, or group key), and a modifier key.

The primary key is variable and should be entered by the user on the keyboard. The secundary key is fixed and is stored in a small plastic module that is fitted into a slot at the upper right of the keyboard. Without this plug-in unit, the Gretacoder 805 can not be used.

The image on the right shows the interior of the secundary key, which consists of the very first 24-pin 1702 EPROM (256 bytes) connected to a DB-25 connector. In order to communicate with another Gretacoder 805, both machines need to have an identical secundary key module [4].
Interior of the secondary key

Secundary keys offer a way of customization. At the time, users could order pre-programmed sets of key modules from Gretag. For larger customers a special programming kit was available. It could be used to generate new unique keys and to make duplicates from existing keys [2].

Secundary key Secundary key Interior of the secondary key Secundary key ready to be erased Close-up of the EEPROM Secundary key on top of the Cretacoder 805 Placing the secondary key Secundary key fitted in the Gretacoder 805

Modular design
The Gretacoder 805 had a truly modular design, which made it possible to create a variety of solutions, ranging from the highly portable briefcase version featured on this page, to a fully fledged desktop workstation. The main unit, i.e. the electronic micro-processor-based crypto heart of the 805 family, was used in every every. The various modules were available in two colours: bright yellow (as shown below) and neutral grey. The basic modules are shown here:

The main unit could be fitted inside a slim-line Samsonite briefcase of the era, together with an acoustic modem or a miniature thermal printer. An example of the portable version is shown at the top of this page. For the desktop version a larger interface case was available. It could hold the main unit, plus one add-on unit to its left. A large page printer could be placed on the top and an optional paper-tape reader/puncher could either be placed on the left or on the right [2].

  • Main Gretacoder 805 unit
  • Acoustical coupler
  • Telex interface
  • Empty case (for desktop version)
  • Miniature thermal printer
  • Desktop interface (for desktop version)
  • Page printer
  • Papertape rader/puncher
  • Samsonite attache case
The Gretacoder 805 is well built and contains only first-class electronic components. After removing the top cover, the interior becomes visible. The electronics consists of a large motherboard at the bottom, a separate keyboard and a set of power supplies at the rear.

The unit shown here was built around 1984. The main circuit is built around an P8080A micro processor, built by AMD in 1979 [5]. Above the 8080 is an SN74S428N controller/bus driver [7].

Main memory consists of 16 HM-6514 static RAM chips of 1024 x 4 bits each (8KB), and a series of EPROMs that contain the software. The image on the right shows a close-up of the three main EPROMs. Although the PCB was designed for eight EPROMs, only three positions are used. The 2732 type EPROMs (4KB) replaced the earlier 2708 (1KB) and 2716 (2KB) types.
Close-up of the EPROMs

As the Gretacoder 805 features static memory [8], data can be retained by a set of rechargeable NiCd cells when the machine is switched off. The NiCd cells are located in front of the RAMs and can easily be replaced as they are mounted in sockets.

Interior of the Gretacoder 805 Keyboard removed from the case The motherboard inside the main unit Top view of the motherboard Close-up of the EPROMs Clock oscillator Display connector

Technical specifications
  • Operating temperature range: 0°C to 50C
  • Storage temperature range: -25°C to 70C
  • ASCII keyboard with auto-letter shift in Baudot mode
  • 37 character smotth-scrolling plasma display
  • Battery-backed RAM
  • 4033 characters plaintext memory
  • 7563 characters ciphertext memory
  • Memory for 8 primary keys
  • Encryption/decryption: 300 ch/s
  • Page printer: 30 ch/s
  • Papertape reader: 120 ch/s
  • Papertape puncher: 40 ch/s
  • Algorithm: sophisticated proprietary non-linear stream cipher [2]
  • 8 primary keys (16 characters each)
  • Secundary key stored in EPROM module
  • Primary key: 4.3 x 1022
  • Secundary key: 1.7 x 1038
  • Modifier key: 1.4 x 1014
Compatible machines
The following machines are known to be compatible with the GC-805:
  • Gretacoder 805 (Desktop version of the above machine)
  • Gretacoder 905 (Pocket cipher machine with LEDs)
  • Gretacoder 906 (Pocket cipher machine with LCD)
  • Gretacoder 505 / SP300 GCA (Huge teleprinter-style cipher machine)
Gretacoder 805 (portable version)

Help required
We are still looking for the User Manual and the Technical Manual of the Gretacoder 805. If you can help, please contact us. Especially the user manual would be of much help as we want to bring the machines back to life again. Any other kind of help would also be much appreciated.

Similar machines
Although the Gretacoder 805 is not compatible with any other brand of cipher machines, there are some machines of the same era that show great resemblance to it. For example:

The Hagelin HC-530 portable electronic cipher macine The Philips Miniflex inside a Samsonite briefcase Philips Picoflex

  1. Jane's Military Communication 1986
    ISBN: 0-7106-0824-1

  2. Gretag Limited, Gretacoder 805, Modular High Security Off-Line Encryption System
    Full-colour 6-pages sales brochure. May 1984.

  3. Gretag Litimed, Gretacoder 805, Modular High Security Off-Line Encryption System
    Earlier (B&W) version of the above brochure. September 1978.

  4. Advanced Micro Devices (AMD), AM1702A datasheet
    Date unknown. Retrieved July 2012.

  5. Advanced Micro Devices (AMD), AM9080A microprocessor datasheet
    May 1987. Retrieved July 2012.

  6. Advanced Micro Devices (AMD), D8255 Programmable Peripheral Interface
    1999. Retrieved July 2012.

  7. Texas Instruments (TI), SN74S428N Datasheet
    October 1976. Retrieved July 2012.

  8. Intersil, HM-6514/883 datasheet
    March 1997. Retrieved July 2012.
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Crypto Museum. Last changed: Monday, 01 October 2012 - 12:45 CET.
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