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TC-803
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 1970 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.

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.
  
Gretag TC-803 cipher machine with strip printer

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.

Samsonite briefcase with Gretag TC-803 cipher machine Gretag TC-803 teletype encryptor in Samsonite briefcase TC-803 teletype encryptor (right) with printer (left) Gretag TC-803 cipher machine with strip printer Printer Model and serial number Printer Expansion connector (PG)
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Samsonite briefcase with Gretag TC-803 cipher machine
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Gretag TC-803 teletype encryptor in Samsonite briefcase
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TC-803 teletype encryptor (right) with printer (left)
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Gretag TC-803 cipher machine with strip printer
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Printer
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Model and serial number
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Printer
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Expansion connector (PG)

Features
The diagram below provides a quick overview of the controls and connections of the TC-803. The device is permanently mounted inside a Samsonite briefcase from within it can be operated. It can be powered from the 110 or 220V AC mains, or from an external 12V DC source, selectable with rotary switches at the right side. At the front is a full keyboard, with high-quality reed switches. 1 Behind the keyboard is a row with toggle switches, red push-buttons and white indicator lamps.


At the top right of the keyboard is a 25-way sub-D socket for connection of the accessories, such as the TP-803 tape puncher, the TR-803 tape reader and the TA-803 teletype adapter. Behind the keyboard – at the centre of the unit – is a 50-way socket for connection of a block with user-defined secret wiring, which adds approx. 1023 combinations to the total key space of the cipher.

The machine can also generate a unique (non-secret) message key — here known as the auxiliary key — using an internal random number generator, under control of an internal switch on one of the PCBs. At the left is a printer which delivers the output onto a pressure-sensitive paper strip.

  1. A reed switch is a hermetically sealed magnet-operated electric switch.  Wikipedia

Slot for user-defined secret wiring, indicator lights and mode selectors MODE switch, push-buttons and power switch Expansion connector (PG) Right side with access to the PSU PSU at the right side (behind the keyboard) Printer with pressure-sensitive paper Print head Paper pulley with pinch roller
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Slot for user-defined secret wiring, indicator lights and mode selectors
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MODE switch, push-buttons and power switch
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Expansion connector (PG)
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Right side with access to the PSU
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PSU at the right side (behind the keyboard)
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Printer with pressure-sensitive paper
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Print head
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Paper pulley with pinch roller

Setup
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.


Compromise
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.

  1. 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].

Parts
Samsonite briefcase TC-803 cipher machine TP-803 tape puncher TR-803 tape reader TC-803 Teleprinter adapter Instruction manuals Pressure-sensitive paper strip User-definable permutation key
Key
Briefcase
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).
  
Samsonite briefcase with Gretag TC-803 cipher machine

Cipher machine   TC-803
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

  
Gretag TC-803 cipher machine with strip printer

Strip printer
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.

  
Printer

Tape puncher   TP-803
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

  
TP-803 tape puncher

Tape reader   TR-803
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

  
Control panel of the TR-803 tape reader

Teletype adapter   TA-803
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

  

Instruction manuals
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

  
Manuals

Paper supply
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.

  
Pressure-sensitive paper

Permutation key
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.

  

Development
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.
  
Early prototype of the TC-803. Crypto Museum Archive CM-303057.

TR-803 tape reader Control panel of the TR-803 tape reader Buttons on the TR-803 Instructions inside the lid of the TR-803 tape reader Pressure-sensitive paper Pressure-sensitive paper
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TR-803 tape reader
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Control panel of the TR-803 tape reader
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Buttons on the TR-803
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Instructions inside the lid of the TR-803 tape reader
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Pressure-sensitive paper
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Pressure-sensitive paper






Interior
The TC-803 is permanently mounted inside a standard Samsonite briefcase of the 1970s. The interior can be access 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.

After removing the cover, 7 vertically mounted PCBs become visible, just behind the keyboard. They are slotted into a back­plane (motherboard) that runs across the bottom of the device. The middle board has a red switch at the right, which can be used to switch the auxilary key on or off.

To the right of the PCBs is a mains power supply unit (PSU) of which the AC mains filter is directly visible. It is suitable for 110 and 220V AC. The device can also be powered from 24V DC, e.g. a truck battery, but this requires the red AC/DC selector (right side) to be set to the DC position.
  
7 PCBs with the electronic circuits

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.

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.
  
Printer with pressure-sensitive paper

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.

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.
  
Printer electronics

The device does not contain a microcontroller and is therefore not driven by software. Instead, all cipher operations are implemented in discrete logic — located on the seven plug-pin boards — largely consisting of
TTL
Integrated Circuits (ICs) of the 7400-series. The frontmost board holds the interface to the 50-way socket at the top, in which the permutation key should be installed. The socket is wired to the inputs and outputs of six SN7495 4-bit shift registers [2]. By wiring the key differently, the operation of the shift registers can be altered in more than 16 million ways.


Interior 7 PCBs with the electronic circuits 7 PCBs installed in the slots of the motherboard (at the bottom) Auxiliary key switch (shown in ON position) Buzzer (with legend for the red AUX switch) Power supply unit (PSU) with cooling fan Mains filter - PSU Cooling fan (with plastic bag containing spare fuses)
Bottom side Printer electronics Backplane (bottom side) Keyboard electronics Permutation key interface Close-up of the wiring Printer with pressure-sensitive paper Print head
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Interior
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7 PCBs with the electronic circuits
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7 PCBs installed in the slots of the motherboard (at the bottom)
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Auxiliary key switch (shown in ON position)
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Buzzer (with legend for the red AUX switch)
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Power supply unit (PSU) with cooling fan
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Mains filter - PSU
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Cooling fan (with plastic bag containing spare fuses)
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Bottom side
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Printer electronics
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Backplane (bottom side)
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Keyboard electronics
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Permutation key interface
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Close-up of the wiring
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Printer with pressure-sensitive paper
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Print head

Specifications
Cipher machine   TC-803
  • 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
Tape puncher   TP-803
  • 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
Tape reader   TR-803
  • 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
Documentation
  1. Business Coder 803, folder (English)
    System overview. Gretag, February 1971.
     French version (March 1974)

  2. TC-803 off-line cryptographic system, leaflet (English)
    Page from full-colour company brochure. Gretag, May 1974.

  3. TC-803 Cryptographic Unit, leaflet (English)
    Gretag, February 1971. 2 pages.

  4. TP-803 tape perforator, leaflet (English)
    Gretag, February 1971. 2 pages.

  5. TA-803 teletype adapter, leaflet (English)
    Gretag, February 1971. 2 pages.

  6. TR-803 tape reader, leaflet (English)
    Gretag, February 1971. 2 pages.

  7. TC-803, Bedienungsanleitung (short, German)
    Gretag, date unknown. A5 landscape, 38 pages.

  8. Off-line Chiffriergeraet TC-803, Bedienungsanleitung
    Full instruction manual of all system components (German).
    Gretag, January 1970. A4 portrait, 68 pages.
References
  1. Gerhard Sulger Buel, TC-803, documentation and background information
    Personal correspondence, June 2013.

  2. Motorola, SN74LS95 4-bit shift register, datasheet
    Date unknown. Retrieved April 2019.

  3. 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.

  4. Wikipedia, Linear-feedback shift register
    Retrieved April 2019.

  5. 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.

  6. Willi Meier and Othmar Staffelbach, Fast Correlation Attacks on certain Stream Ciphers
    1989. Journal of Cryptology, 1(3), pp. 159—176.

  7. Willi Meier und Othmar Staffelbach, Kryptographie und elliptische Kurven
    Elemente der Mathematik, 52 (1997) pp. 137—151.

  8. Jaap van Tuyll, personal correspondence
    Retrieved April 2019.
Further information
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Crypto Museum. Created: Friday 29 June 2012. Last changed: Saturday, 20 April 2019 - 07:12 CET.
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