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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 desktop version in the common neutral gray colour. It consists of the main unit, placed inside an interface cabinet, a storage box (to the left of the keyboard), a large page printer (on top) and a papertape reader/puncher on the left.

The main unit is identical to the suitcase version. It is microprocessor-based, has a full QWERTY keyboard and a red alpha-numerical plasma display. The memory can hold messages up to 4000 characters. The output can be printed on the wide page printer that is mounted on top.
Complete Gretacoder 805 desktop system with paper tape reader/puncher on the left

For security, a two-part cryptographic key was used, consisting of a 16-character primary key that was entered by the user and a fixed secundary key that was stored inside a plug-in module. When in operation, the plug-in module had to be present inside a slot to the right of the display.

Data can be recorded to the (optional) papertape puncher that was constructed in such a way that it could be placed at either side of the main unit. It uses standard 5-hole telex papertape and stores the information in the common Baudot standard. A built-in papertape reader can be used to play back recorded messages. The papertape can also be transmitted by an external telex.

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 have survived. The desktop version (shown here) 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.

Front view of the desktop version of the Gretacoder 805 Complete Gretacoder 805 desktop system with paper tape reader/puncher on the left PP-805 page printer for Gretacoder-805 RP-805 papertape reader/puncher for the GC-805 Secundary key Placing the secondary key

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.

The unit featured on this page is currently not functional. It contains a very early motherboard (probably a prototype) with five 2708 EPROMs of 1KB each. Furthermore, the EPROMs contain a different kind of software than other machines in this series. This software was probably intended for demonstrations or for generating punched papertapes only (more about this below).

Main unit
The main unit of the desktop station is identical to that of the portable 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 shows a typical GC 805 main unit in a neutral grey case. A fixed power cable is present at the rear to connect the unit directly to the mains. At the left side is a large 50-pin D-type connector that allows the connection of a peripheral, such as an acoustic modem, a telex interface or small printer.

At the rear is another large connector that allows an external papertape reader/puncher to be connected. For desktop use, the main unit is installed inside a large metal interface frame that makes the whole unit wider and deeper.
Main unit

The empty space to the left of the main unit can be filled by an (optional) peripheral or interface, but also by an empty storage box as in the example shown here. The storage box is bolted to the left side of the main unit. Due to its large lid, it can only be opened when the page printer is not mounted on top of the unit. More information about the optional interfaces can be found below.

The large connector at the rear of the main unit is extended by the interface frame to a similar connector on the top surface, allowing the wide page printer to be placed directly over it. The page printer is constructed in such a way that it mates directly with this connector. The connector carries all the (parallel) data lines and even the 220V AC mains, so that no cables are required.

Main unit mounted inside larger frame with empty box on the left Empty metal frame Main unit Connector at the left side of the main unit Connector at the rear of the main unit Empty storage box (closed) Empty storage box (open) Connector on top of the frame

Page printer
For desktop use, the PP-805 full 80-column wide page printer can be installed. It is placed on top of the main unit and is hold in place by a lock at the rear. The unit is connected to the interface frame by means of a large D-type connector at the bottom that also carries the 220V lines.

The image on the right shows the wide PP-805 printer, which has the same width as the frame (i.e. the main unit plus the storage box). It has four pins at the bottom for holding it in place. The two at the front mate with two square holes in the top cover of the main unit (just above the display), whilst the two at the rear mate with the frame, producing a click when properly seated.

The printer requires no cables and is normally controlled by the main unit. The only controls are the two buttons at the top right: the power switch and a push-button for feeding the paper.
PP-805 Page Printer

The printer case can be opened by raising the metal cover with the handle at the front. This gives access to the actual printer itself, which is slightly smaller than the case. A thin aluminium cover protects the printing machanism. It is fitted to the case by means of a series of springs around the edges. Inside the case is a thermal printer with a rather large motor at the left. The unit prints to 21 mm wide thermal paper that was commonly used with fax-machines in those days.

PP-805 page printer font view PP-805 Page Printer Pape printer with its cover open Protective cover removed Protective cover snaps Controls on the PP-805 printer Rear side of the PP-805 printer Mains voltage selector and fuse
Bottom view of the PP-805 printer Data and power connector (bottom) Front view of the printing mechanism Printer motor Print head transport mechanism Printer mechanism Front foot of the printer (bottom view) Print head and transport mechanism

Papertape reader/puncher
Plain or encrypted messages can be recorded onto papertape by using the (optional) RP-805 papertape reader/puncher, that is constructed in such a way that it can be placed at either side of the main unit. It connects to the main unit by means of a large D-type connector that is fitted at the rear. It also carries the mains voltage.

The RP-805 also contains a papertape reader at the front. It can be used to play back previously recorded messages. It can also be used for the encryption of messages that are prepaired on an external teleprinter or telex machine (off-line).
RP-805 papertape reader/puncher for the GC-805

The unit uses standard 5-hole papertape and follows the common baudot standard. Supply of fresh paper is from a drawer at the bottom of the unit. The drawer can be opened from both sides, allowing the reader/puncher to be placed either at the left or at the right of the main unit.

RP-805 papertape reader/puncher for the GC-805 Papertape reader Papertape puncher Removing the paper-chad container RP-805 with opened paper tape drawer Close-up of the opened papetape drawer RP-805 placed to the right of the GC-805 RP-805 placed to the left of the GC-805

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 a highly portable briefcase version, to the fully fledged desktop workstation featured on this page. The main unit, i.e. the electronic micro-processor-based crypto heart of the 805 family, was used in every version. 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. 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]. An example of the desktop version is shown at the top of this page.

  • 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 (for the portable version)
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 1979. The main circuit is built around an AM9080A micro processor, built by AMD in 1977 [5]. This is basically a military version of the popular Intel 8080A. On later versions of the motherboard the P8080A was often used. To the left of the 8080 is an SN74S428N controller/bus driver [7].

The image on the right shows the keyboard with an AM9555DM peripheral controller. This is an early version of the popular D8255 that was used in later versions of the machine [6]. The ribbon cable connects it to the motherboard.
Keyboard and I/O controller

The unit features 8KB of static RAM, consisting of 16 memory chips of the type HM-6514/9, that contain 1024 x 4 bits each. As this is static memory, it can be retained by a set of rechargeable NiCd cells when the machine is switched off The cells are mounted in front of the RAMs [8].

To the rear of the RAM chips are 8 sockets for ROMs or EPROMs. In the first release of the motherboard 1KB EPROMs were used (2708), but in later version only three 4KB types were used (2732). The other sockets were not populated. These larger EPROM can not be fitted on the older motherboards, due to an error in the PCB layout. This problem is fixed in later versions.

Interior of the GC-805, with the keyboard present Interior of the GC-805 (keyboard removed) Keyboard and I/O controller Disconnecting the keyboard Top view of the motherboard AM9080A processor and bus controller Close-up of the battery-backed RAM banks Display connector

The machine featured on this page is currently not functional. It is equipped with a different set of EPROMs than our portable version, has an older type of motherboard (probably a prototype) and has no dongle. Furthermore, some of the text above the top row of the keyboard has been removed. It is likely that this machine was used as a data-entry station for punched tape. In the meantime, please refer to the portable version for more information about its operation.

The challenge is now to restore the machine to its full glory again. This involves modifying the motherboard to accept the larger EPROMs used in the later machines, making copies of the existing EPROMs and creating a replacement plug-in module for the secundary key. Whenever we have made some progress, we will report it on this page.

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 (Portable 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.
Further information
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Crypto Museum. Last changed: Monday, 01 October 2012 - 12:44 CET.
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