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Crypto Data Telex Gretag
Off-line teleprinter encryptor
TC-803, also known as Telecrypto 803, as Gretacoder 803 and as Business Coder,
was a semi-portable off-line encryption device for
teletypewriter signals,
developed around 1968 by Gretag
in Regensdorf (Switzerland). It is basically an electronic
teletypewriter,
with a built-in electronic cipher machine,
that was intended for law-enforcement, government and for diplomatic traffic.
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The actual cipher machine (TC-803),
is housed in a standard Samsonite briefcase
of the era, as shown in the image on the right. At the bottom
right is a high-quality keyboard with QWERTZ layout,
MODE selectors and indicator lamps.
To the left of the keyboard is a built-in printer,
which delivers the output of the cipher onto a narrow paper strip
that leaves the device at the left.
Additional accessories were available for
storing the output
onto punched paper tape, for reading back
punched paper tapes and for
connecting a standard teleprinter to the device.
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The system uses the
CCITT No. 2 teleprinter standard
— also known as ITA-2
or Baudot
— which makes it compatible with virtually
any teletype network in the world.
Development of the TC-803 started in the late 1960s, with
the first machines available for sale in January 1970 [H].
It was the first fully electronic cipher machine developed
by Gretag AG,
that used Non-Linear Feedback Shift-Registers (NLFSRs).
There are indications that the cipher was attacked, but it is
currently unknown whether it was broken.
In 1979, the TC-803 was succeeded by the improved
Gretacoder GC-805.
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A reed switch is a hermetically sealed magnet-operated electric switch.
➤ Wikipedia
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In the most simple configuration, the TC-803 is used on its own, powered
from the AC mains, and not connected to any other device. The plaintext
is entered on the keyboard and printed on a paper strip as a cryptogram.
The cryptogram is then sent by other means, for example by regular mail,
by courier, or re-typed on a teletype terminal. In the same vein, a received
cryptogram has to be entered on the keyboard, after which the built-in
printer produces the plaintext again.
To make the reception of messages easier — in particular when receiving
a large number of messages frequently — an external
tape reader (TR-803)
can be connected to the PG socket of the cipher machine. It allows a
received cryptogram — typically received on a teletype and punched to tape —
to be entered into the cipher machine, as if it was typed on the keyboard.
For the transmission of a large number messages, it was possible to connect
an external tape puncher
to the PG socket of the cipher machine, as shown in the diagram above.
It stores the message directly onto 5-level punched paper tape. The tape
puncher also has a PG socket (identical to the PG socket of the cipher
machine), so that the tape reader can be chained to it.
In situations where the TC-803 cipher machine had to be used frequently
on a permanent basis, it was possible to connect it directly to the existing
teletype equipment, by installing the
TA-803 teletype adapter, as shown in the diagram above.
The adapter has connections for an external teletype machine,
as well as a PG socket for connection of the
TR-803 tape reader.
In this setup, the TP-803 tape puncher
was omitted, as it was generally present on the external teletype.
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The TC-803 was used in many non-NATO countries, like Brasil, Venezuela,
Argentina, Lybia and Morocco, and also in Spain.
The cipher had the attention of the
Cuban intelligence service (DGI),
as in 1983 they shared descriptions of the machine, its procedures and its
cryptanalysis with the
Ministerium für Staatssicherheit
— the repressive Stasi — of the former DDR (East Germany) [3].
It is currently uncertain though, whether the
DGI or the MfS (Stasi) managed to break the cipher.
Like many contemporary cipher machines — such as the
Hagelin H-460,
the Datotek DC-105
and DC-26,
the Siemens T-1000CA
and the TST-9669 —
the crypto logic of the Gretag TC-803 is constructed of a series of
Linear Feedback Shift Registers (LFSRs) [4]. The length of each LFSR and the position
of its taps are choosen in such a way, that a maximum length
key stream is achieved.
Furthermore, the cipher is usually strengthened by adding non-linear
operations to it (NLFSR).
In June 2018, at the 1st Conference on Historical Cryptology in Uppsala (Sweden),
former Dutch cryptanalyst Jaap van Tuyll explained that a cipher based
on LFSRs could be attacked successfully, with a method that was known in the 1980s [5].
The method was described in 1989 by Willi Meier and Othmar Staffelbach [6],
but had been known to cryptanalists for some time [5].
According to Jaap van Tuyll, The TC-803 was more complex, and could
not be solved with this method [8].
Interestingly, the research and publication of the above attack in the
Journal of Cryptology 1(3) of 1989, was supported in part by
Gretag AG [6].
At the time, Othmar Staffelbach 1 was cryptologist at Gretag AG.
It is likely that their findings led to improvements in later cipher algorithms,
such as improvements of the non-linear properties.
The weaknesses of simple LFSR-based systems had already been known
by Gretag AG for some time however,
as its successor — the Gretacoder 805
(introduced in 1979) — was specifically advertised as having
a non-linear cipher algorithm.
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Othmar Staffelbach was born in 1952 and studied math at the ETH in Zürich
(Switzerland) where he graduated in 1983 on the topic of Algebraic Topology.
From 1983 to 1994 he worked for Gretag
in Regensdorf (Switzerland) as a cryptologist, before joining the
General Staff of the Swiss Army [7].
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The TC-803 cipher machine itself is mounted permanently in an unobtrusive
Samsonite briefcase of the early 1970s. It allowed intelligence and
diplomatic personnel to travel around the world conveniently and inconspicously.
The briefcase measures 46 x 33 x 12 cm and weights approx. 12 kg (with cipher
machine).
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The image on the right shows the actual TC-803 cipher machine, mounted inside
a Samsonite briefcase. At the left is the paper strip printer.
The device is powered directly from the mains and can be used on its own,
as an off-line cipher machine. When only a few messages had to be processed,
it was assumed that the cryptogram would be entered manually, via the keyboard
at the front. When processing high-volume traffic, it was recommended to use
a tape reader.
➤ Read datasheet
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The TC-803 comes with a built-in impact printer, that delivers the text onto
a pressure-sensitive paper strip. The printer is a standalone unit that is
mounted inside the Samsonite briefcase,
to the left of the cipher machine.
At the front is a linear print head that consists of 8 lines with 8 different
characters each, allowing a total of 64 different characters to be printed.
The printing mechanism is under control of 7 solenoids, three of which control
the rotation of the print head, whilst three others control the horizontal
position. One controls the impact.
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When sending a large number of messages, it was possible to store the
encrypted messages onto a punched paper tape, so that they could be sent
from a regular teletype machine (or line-connected tape transmitter), without
the need to re-type the cryptograms on the teletypewriter.
For these situations, the TP-803 tape puncher shown in the image on the
right was available. It was connected to the 25-way socket marked PG at
top right of the keyboard of the TC-803.
➤ Read datasheet
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In the same vein, the TR-803 tape reader was available for entering high-volume
cryptograms directly into the TC-803, without the need to re-type them on the
keyboard of the TC-803.
The tape reader can be connected directly to the 25-way PG socket
of the cipher machine,
or to the (identical) PG socket
of the tape puncher.
➤ Read datasheet
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With the optional TA-803 teletype adapter, the TC-803 cipher machine could
be connected to virtually any teletypewriter in the world, as long as it
supported the international ITA-2 standard.
The adapter is housed in a metal enclosure that matches the design of the
cipher machine.
A built-in automatic line-end control, breakes a continuous text down into
telex lines with a maximum length of 69 characters each.
➤ Read datasheet
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When the TC-803 was introduced early in 1970, it came with a full instruction
manual in which the cipher machine and all accessories were described. Later
releases of the operator's manual were split into several parts.
Although only the German version of the manual has been recovered so far, it is
believed that the operating instructions were available in various other
languages, including English and French.
➤ Download the manual
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The printer requires a special type of pressure-sensitive paper with a
width of 8.2 mm. It was supplied on rolls with an 80 mm
diameter (inner diameter 25 mm),
that was installed on the spool at the rear
of the printer. Each paper roll was suitable for printing
approx. 22,000 characters at a speed of 10 characters per second.
The image on the right shows the only fresh paper roll that we have in
our collection at the moment. If you know about a source for this paper,
please let us know.
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A secret permutation key should be installed in the 50-way socket behind
the keyboard. Without this key, the TC-803 can not be used.
The key contains 23 user-configurable wire loops.
It is the only part of the system that is secret, and should normally be
stored separately from the machine. For this reason, it is constructed
in such a way, that the briefcase can only be closed if the permutation key
is removed.
The permutation key is currently missing from our system.
The wiring details are unknown.
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Development of the TC-803 was started in the late 1960s, when solid-state
electronics were rapidly becoming an accepted alternative for regular valves
(tubes) and mechanical solutions.
The image on the right shows an early prototype of the late
1960s. On this version, the keyboard is at the left, and the MODE selectors
are in front of the keyboard, which probably caused ergonomic problems.
The printer – here positioned on the right – remained unaltered.
This version was probably known as the TC-800.
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The TC-803 is permanently mounted inside a standard
Samsonite briefcase
of the 1970s. The interior can be accessed from the top of the device,
when the lid of the briefcase is open. Remove the only screw in the top
surface of the cover, and then slide the cover towards the keyboard.
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At the rear right – behind the PSU – is a rather large
cooling fan.
This was necessary, as the early TTL ICs of the 1960s and 70s produced
quite a bit of heat. Also at the rear — to the left of the fan
— is a buzzer,
with a label that explains the meaning of the
red switch on the middle board.
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At the left is the strip printer
that is housed in its own metal enclosure. At the front of the
printer is a cylindrical print head
that consists of eight linear rows with 8 characters each. Three of the
solenoids control the horizontal position of the print head (23).
Three other solenoids are used to select one of the eight surfaces
by controlling the angle of the print head (23).
The solenoid at the centre controls the impact of the hammer.
At the rear is a horizontal reel with the
impact-sensitive paper strip.
The paper is guided past the right side of the printer, towards
the front.
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The paper is then guided between the hammer and the print head,
and leaves the machine at the left side.
It will be difficult to find suitable paper for this printer,
as the rolls are no longer being manufactured. The printer is covered
by a metal panel, that is held by two clamps at the rear.
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The remaining electronic circuits are located at the
bottom of the device.
They can be accessed by removing two screws between the front edge
of the keyboard and the edge of the briefcase, and lifting the entire
device from the briefcase.
At the bottom are the backplane –
that holds the seven vertical PCBs at the top
– the mains power transformer,
the keyboard electronics
and the printer electronics,
as illustrated in the diagram below. The black metal shield in the
upper right corner, hides the solenoid drivers of the printer. The printer
wiring is fixed to the cipher machine.
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Device Portable electronic cipher machine Manufacturer Gretag AG Users Brasil, Venezuela, Argentina, Lybia, Morocco, Spain Algorithm Proprietary Elementary key 10 letters entered on the keyboard ~1014 Auxiliary key 10 letters generated at random (non-secret) Secret wiring 50 pin connector (wiring determined by user) ~1023 Keyboard QWERTZ, 53 keys with reed switches Printer 10 characters/sec, pressure-sensitive tape Power 110/220V AC ±15% (120 Watt), 50/60 Hz ±10% Cables Mains power cable Radiation TEMPEST filtering Temperature 0° to +50°C (storage: -30° to +70°C Dimensions 46 x 32 x 13 cm Weight 12 kg
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Paper Standard 5-level CCITT Code No. 2 (ITA-2) Speed ≤ 16 characters/sec Power 110/220V AV ±15% (50 Watt), 50/60 Hz ±10% Cables Interconnection cable (PG), mains power cable Radiation TEMPEST filtering Temperature 0° to +50°C (storage: -30° to +70°C) Dimensions 30 x 24 x 23 cm Weight 10 kg Radiation TEMPEST filtering
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Paper Standard 5-level CCITT Code No. 2 (ITA-2) Speed ≤ 20 characters/sec Power From cipher machine or tape puncher Cables Interconnection cable (PG) Temperature 0° to +50°C (storage: -30° to +70°C) Dimensions 16.5 x 16 x 10.5 cm Weight 1.7 kg
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- Business Coder 803, folder (English)
System overview. Gretag, February 1971.
➤ French version (March 1974)
- TC-803 off-line cryptographic system, leaflet (English)
Page from full-colour company brochure. Gretag, May 1974.
- TC-803 Cryptographic Unit, leaflet (English)
Gretag, February 1971. 2 pages.
- TP-803 tape perforator, leaflet (English)
Gretag, February 1971. 2 pages.
- TA-803 teletype adapter, leaflet (English)
Gretag, February 1971. 2 pages.
- TR-803 tape reader, leaflet (English)
Gretag, February 1971. 2 pages.
- TC-803, Bedienungsanleitung (short, German)
Gretag, date unknown. A5 landscape, 38 pages.
- Off-line Chiffriergeraet TC-803, Bedienungsanleitung
Full instruction manual of all system components (German).
Gretag, January 1970. A4 portrait, 68 pages.
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- Gerhard Sulger Buel, TC-803, documentation and background information
Personal correspondence, June 2013.
- Motorola, SN74LS95 4-bit shift register, datasheet
Date unknown. Retrieved April 2019.
- Jörg Drobick, Dokumentierte Kompromittierung von Chiffriergeraten
Website SAS und Chiffrierdienst. Retrieved April 2019.
BStU, MfS — Abt. X Nr. 000319, HA III Nr. 011096, BdL Nr. 000974.
- Wikipedia, Linear-feedback shift register
Retrieved April 2019.
- Jaap van Tuyll, Design and Strength of a Feasible Electronic Ciphermachine ... 1970s
Proceedings of the 1st Conference of Historical Cryptology, pp. 153—158.
Uppsala (Sweden), 18-20 June 2018.
- Willi Meier and Othmar Staffelbach, Fast Correlation Attacks on certain Stream Ciphers
1989. Journal of Cryptology, 1(3), pp. 159—176.
- Willi Meier und Othmar Staffelbach, Kryptographie und elliptische Kurven
Elemente der Mathematik, 52 (1997) pp. 137—151.
- Jaap van Tuyll, Personal correspondence
Retrieved April 2019.
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© Crypto Museum. Created: Friday 29 June 2012. Last changed: Tuesday, 14 February 2023 - 21:22 CET.
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