Electronic off-line cryptographic system
Gretacoder 805 – also known as GC-805 – was a flexible modular
off-line system for encrypting and decrypting messages,
developed in the late 1970s by Gretag
(later: Gretacoder Data Systems)
in Regensdorf (Switzerland), as the successor to the
It was one of the first fully electronic microprocessor-based cipher machines.
Due to the modular approach,
different configurations of the Gretacoder 805
were possible, ranging from small portable briefcase-based systems
to large fixed desktop setups,
complete with a page printer, a paper tape reader and a tape puncher
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.
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
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 .
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.
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.
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.
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
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.
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 .
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 .
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
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 .
- 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 .
Above the 8080 is an SN74S428N controller/bus driver .
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 ,
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.
- Operating temperature range: 0°C to 50°C
- Storage temperature range: -25°C to 70°C
- 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 
- 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
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)
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.
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:
Any links shown in red are currently unavailable.
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© Crypto Museum. Created: Saturday 31 July 2010. Last changed: Sunday, 31 March 2019 - 11:45 CET.