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Gretag Switzerland
Portable electronic cipher machine
Gretacoder 905, also known as GC-905, was a portable electronic
cipher machine,
introduced in 1976 by Gretag AG in Regensdorf (Switzerland).
The device is intended for off-line use and allows text messages
to be encrypted and decrypted one character at a time, using just three buttons.
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The device measures 197 x 120 x 40 mm and weights just 600 grams.
At the top is the display that consists of 32 LEDs. Messages may
contain letters, numbers and punctuation marks, but the ciphertext
consists of the Latin letters A-Z only.
At the right is the MODE selector that allows the mode of operation
to be selected: OFF, Encipher or Decipher.
At the left is a large white field that is used to select the input-letter.
Press at the left or right, to step through the available characters
in both directions. Once the desired character is illuminated, press the small
circular input key.
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This will cause the input letter to be encoded. The output letter will
now start flashing on the display (as long as the input key is depressed).
This method is used for enciphering, deciphering and for entering the
Elementary Key. Full instruction can be found in
one of the user manuals
[B].
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Gretacoder 905 was developed during the course of 1975 and was
announced early in 1976. Like most Gretag cipher equipment,
it was hated by the US
National Security Agency (NSA),
as it was unreadable to them. 1
The NSA had tried to get control over Gretag's algorithms,
but to no avail.
In order to gain control of the crypto market, the American CIA
and the German BND then decided that competitor
Crypto AG
— which they fully owned and controlled
— should come up with
a portable device that could compete with the Gretacoder 905
and could lure customers away.
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The competing device — the Hagelin HC-520
— was developed by Siemens
and was introduced in 1977. CIA
and BND hoped that potential users would prefer
the HC-520
over the Gretacoder [1].
The Gretacoder 905 was succeeded in 1981 by the
Gretacoder 906,
which had a full keyboard.
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In this context, unreadable means that the device could not be
broken by the NSA. Also known as unfriendly or secure.
In contrast: algorithms that can be broken, are known as
readable or friendly.
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Although the Gretacoder 905 looks like a simple and perhaps crude device,
it offered excellent security for its time. Operation was similar to that of the
mechanical devices of the 1950s, like the Hagelin CX-52. The fact that
a message are encrypted letter-by-letter was a disadvantage,
but was at the same time a blessing in disguise. It forced its users to
keep the messages short, and as a general rule of thumb, short messages
are more difficult to break than longer ones.
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The block diagram below shows how the GC-905 works. Note that it does not
contain a microcontroller or any software whatsoever. Instead, it is
fully built with discrete CMOS logic, and is controlled by various internal
state machines. The block diagram is based on the description of its
operation in US Patent 4,068,089.
For a detailed description, please refer to
that patent.
At the bottom are the controls: two push-buttons (left/right) for selecting
the desired character, a push-button for entering the selection and stepping
the state machine, and a rotary switch for selecting between encoding and
decoding. Selecting the middle position switches the device off.
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The Gretacoder 905 is housed in a dark green plastic enclosure that consists
of two case shells: the top half and the bottom halve. The two halves are held
together by four M3 screws, that are accessible from the bottom. They might be
protected by wax seals that have to be removed first.
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Once the four screws have been removed, the bottom case shell can be removed,
after which the interior is exposed. The complete
assembly may now be removed from the upper case shell. It consists of
three printed circuit boards (PCBs)
and a holder for four 1.5V AA-size batteries.
The image on the right shows the complete assembly. The three PCBs are held
together by red aluminum mounting stubs with C-clips in the four corners.
They are interconnected by means of short (fixed) ribbon cables. At the
top is the display board. It holds the 32 red LEDs.
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Device Pocket cipher machine Principle Electronic, shift-registers Manufacturer Gretag (Switzerland) Model Cretacoder 905 Alphabet Latin (other alphabets on request) Cryptogram Letters only Display 32 LEDs Modes Off, Cipher, Decipher Period ≈ 108 (minimum) Power 4 × battery 1.5V (AA-size, type UM-3) Temperature -20°C to +55°C (storage +40°C to +70°C) Dimensions 197 × 120 × 40 mm Weight 600 g
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Structure PROM (user programmable read-only memory) ≈ 109 Elementary 10 letters, determined by user = 2610 ≈ 1.4 · 1014 Auxiliary 10 letters, automatically generated 1 = 2610 ≈ 1.4 · 1014
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- Military-grade case
- Power supply unit (PSU) 110/220V AC
- Programmaing unit for PROM
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At the start of each cryptogram.
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The same patent is registered in Germany, France, United Kingdom,
Japan, Netherlands, Norway and Sweden.
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- Gretacoder 905 Operating Manual — draft
Gretag Ltd., date unknown.
- Gretacoder 905 Operating Manual — final version
Gretag Ltd., September 1976.
- Gretacoder 905, sales leaflet (English)
Gretag Ltd., March 1976.
- Gretacoder 905, sales leaflet (German)
Gretag Ltd., March 1976.
- Gretacoder 905, sales leaflet (French)
Gretag Ltd., March 1976.
- Gretacoder 905, sales leaflet (Spanish)
Gretag Ltd., March 1976.
- Wartungskonzeption Gretacoder 905
Gretag AG, F. Christen, 26 January 1976.
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© Crypto Museum. Created: Wednesday 26 February 2020. Last changed: Sunday, 14 January 2024 - 17:41 CET.
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