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Gretacoder 805
Electronic off-line portable cipher machine

Gretacoder 805, also known as GC-805, is a high-end modular off-line system for encrypting and decrypting messages, developed around 1978 by Gretag (later: Gretacoder Data Systems) in Regensdorf (Switzerland) as the successor to the TC-803. It was one of the first fully electronic microprocessor-based cipher machines. Due to its modular approach, different configurations were possible, ranging from a portable device with thermal printer or acoustic modem housed in a briefcase, to a desktop setup with page printer and punched paper tape reader/puncher [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 secondary 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.
  

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.

 Check out the desktop version

PLEASE HELP — We are still looking for the User Manual and the Technical Manual of the Gretacoder 805. If you have any of these, please contact us. Especially the user manual would be greatly appreciated as we want to bring the machines back to life again. Any other kind of help would also be much appreciated.
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
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The Gretacoder 805 inside a standard Samsonite briefcase
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Portable version of the Gretacoder 805
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Gretacoder 805 main unit
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Front view of the main unit
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Close-up of the electronic key block
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The lid of the printer
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The thermal printer of the Gretacoder 805
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The thermal printer of the Gretacoder 805

Features
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 [A]. 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 secondary 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.
  

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

Thermal 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.
  

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)
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Small thermal printer (closed)
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Small thermal printer (open)
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Small storage compartment
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Opening the storage compartment
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Placing the mains plug inside the storage compartment
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The mains plug stored inside the storage compartment
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The printer mounted to the left side of the main unit
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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 secondary 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 secondary 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 secondary 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 secondary key module [a].
  

Secondary 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 [A].

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
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Secundary key
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Secundary key
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Interior of the secondary key
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Secundary key ready to be erased
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Close-up of the EEPROM
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Secundary key on top of the Cretacoder 805
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Placing the secondary key
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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 [A].


Modules
  • 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
Interior
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 [b]. Above the 8080 is an SN74S428N controller/bus driver [d].

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.
  

As the Gretacoder 805 features static memory [e], 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
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Interior of the Gretacoder 805
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Keyboard removed from the case
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The motherboard inside the main unit
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Top view of the motherboard
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Close-up of the EPROMs
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Clock oscillator
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Display connector

Compatible devices
The following machines are known to be compatible with the GC-805:

  • Desktop version of the above machine
  • Gretacoder 505
    TTY encryptor
  • Pocket cipher machine with LCD
  • SP-300/GCA
    Huge teleprinter-style cipher machine
Gretacoder 805 (portable version)
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
Specifications
  • Algorithm
    Proprietary non-linear stream cipher
  • Keys
    Primary key: 16 characters 1
    Secondary key held in EPROM plug-in unit
  • Key space
    ~ 1060
  • Keyboard
    ASCII, Baudot
  • Display
    37 character, smooth scrolling plasma display
  • Memory
    Battery backed
    4033 characters plaintext
    7563 characters ciphertext
    8 primary keys 1
  • Option
    Arabic
  • Temperature
    0°C to +50°C
  • Storage
    -25°C to +70°C
  • Dimensions
    See below
  • Weight
    See below
  1. different primary keys can be held in memory simultaneously.

Briefcase version
  • Power
    96-253V AC
  • Dimensions
    470 × 340 × 95 mm
  • Weight
    8 kg
Desktop version
  • Power
    97-126V and 87-253 V AC
  • Dimensions
    460 × 430 × 180 mm (with printer)
  • Weight
    13 kg
Paper tape reader/puncher
  • Standard
    ITA-2
  • Dimensions
    460 × 200 × 180 mm
  • Weight
    8 kg
Datasheets
  1. Advanced Micro Devices (AMD), AM1702A datasheet
    Date unknown. Retrieved July 2012.

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

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

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

  5. Intersil, HM-6514/883 datasheet
    March 1997. Retrieved July 2012.
Documentation
  1. Gretacoder 805, Modular High Security Off-Line Encryption System
    Full-colour 6-pages sales brochure.
    Gretag Limited, May 1984.

  2. Gretacoder 805, Modular High Security Off-Line Encryption System
    Earlier (B&W) version of the above brochure.
    Gretag Litimed, September 1978.
References
  1. Jane's Military Communication 1986
    ISBN: 0-7106-0824-1
Further information
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Crypto Museum. Created: Saturday 31 July 2010. Last changed: Sunday, 14 January 2024 - 11:37 CET.
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