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Siemens Key Gun
Key storage and transfer device

The Siemens Key Gun 1 is a universal key storage and key transfer device, also known as a filler or a fill gun, developed in the mid-1970s by Siemens in München (Germany), for use with voice encryption devices like the MSC-2001. It is also known by its order number S42043-E522-A2.

The device allows cryptographic keys – that are stored on a 5-level punched paper tape – to be transferred to a compatible encryption device or to a compatible crypto-enabled radio, via the military 14-pin male connector at the front.

The device measures 175 x 90 x 40 mm and weights approx. 500 grams 2 including the 3.4V battery that is used to retain the keys in the internal CMOS memory. On top of the device is a narrow slot, through which a standard 5-level punched paper tape can be pulled at an arbitrary speed. The data is clocked by the sprocket hole.
Siemens Key Gun

The device can be used to transfer key(s) straight from the paper tape to the encryption device, or — when using the A2 model — to store it in one of the key compartments of the device itself, so that it can be transferred to one or more encryption devices later. In case of an emergency, it is possible to wipe all keys in a two-step action. This procedure is known as ZEROIZING. The device is suitable for transferring keys to the Siemens MSC-2001 voice encryption device, to which it can be connected directly. For other devices, a suitable adapter or interface may have to be used.

The device was also used with the Siemens CHX-200 radio station, where it was used for loading the cryptographic keys for encryption and frequency hopping into the CHP-200 processor [1]. The CHX-200 was a high-end military radio system that was available in various configurations. It was suitable for the transmission of morse code (CW), voice (phone), and data (telegraphy, telex).

  1. The device appears not to have a model number. Instead the name Key Gun is used in Siemens litarature.
  2. Valid for the A2 model.

Siemens Key Gun Siemens Key Gun Key tape rader, start button and LED Key compartment selector Connection to cipher equipment Model tag Key gun connected to the remote socket of the MSC-2001 Key Gun with NF-7 fill cable
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Siemens Key Gun
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Siemens Key Gun
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Key tape rader, start button and LED
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Key compartment selector
5 / 8
Connection to cipher equipment
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Model tag
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Key gun connected to the remote socket of the MSC-2001
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Key Gun with NF-7 fill cable

  • S42043-E522-A1
    This is the basic version of the Siemens Key Gun. It has a built-in 5-level paper tape reader that is compatible with the ITA-2 standard, also known as CCITT-2 and Baudot. It is suitable for transferring a key directly from tape to the encryption device. As it does not have a built-in memory, the keys can not be stored inside the device itself.

  • S42043-E522-A2
    This version has the same features as the A1 version described above, but also has a built-in memory. Keys can be transferred from the key tape to the gun, where they are kept in a battery-backed CMOS memory. The gun can then be used to transfer the key(s) to one or more encryption devices. The Siemens Key Gun described here, is of this type.
The diagram below shows the features of the Siemens Key Gun. At the front is a 14-pin male connector that can be fitted directly to the KEY socket of a compatible radio or encryption device. In some cases, a conversion cable has to be used between the Key Gun and the encryption device. This is the case with the Siemens CHX-200 radio station, for which an NF-7 cable is needed.

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At the top of the device is a MODE selector, an indicator light, a START button and a reader for 5-level punched paper tape. The tape should be inserted into the reader from the top, and is pulled through it manually. When doing so, the sprocket hole in the key tape generates a clock pulse to which the internal electronics are synchronised. The MODE dial is used for selecting one of eight key compartments. A data transfer is initiated by pressing the START button.

In case of an emergency it may be necessary to wipe all keys that are stored in the internal memory of the device (A2 model only). This is usually done by means of a two-step procedure. On the Siemens Key Gun, the rotorary selector on top of the device is set to (1), where it is blocked by a white plastic ring mounted below the knob. If knob is then forced pasted the blocked position (i.e. to CODE ERASE), the plastic notch will break and the memory is cleared. This procedure can not be reversed, and the plastic ring has to be replaced afterwards.

Key tape format
The diagram below shows the format of the key tape, which conforms to the ITA-2 standard. The actual cryptographic key consists of 50 bits. As each ITA-2 character is 5-bits long, this means that the key consists of 10 characters. There are leading and trailing characters, plus characters to identify the start and validity of the key. Furthermore extra stunt characters 1 are inserted after each key, to ensure that the teleprinter – on which the key tape is made – is put in a known state.

The tape starts with a leader that consists of approx. 40 x the letter 'V'. This is followed by the start character – the letter 'A' in this case – and the check character, which is always the letter 'J'. The next 10 characters are the actual key words, each of which has 32 possibilities (25 = 32).

As the key words can be any code from the ITA-2 telegraph alphabet, including a figures shift (FIGS), it is necessary to put the teleprinter back in a known state at the end of the KEY. This is done by inserting the reset sequence: letter shift (LTRS), carriage return (CR) and line feed (LF).

There is no checksum and the tape ends with a trailer that consists of approx. 40 x the letter 'V'. If multiple keys (up to 8) are distributed on a single key tape, the trailer is also the leader of the following key. In that case, the start character 'A' – which is used for a single key – should be replaced by a different one that assigns the key to a specific key compartment of the device. The following start characters can be used to address the key compartments 1 to 8:

  • X
    → 1
  • F
    → 2
  • Y
    → 3
  • S
    → 4
  • B
    → 5
  • D
    → 6
  • Z
    → 7
  • E
    → 8
  1. In telegraph speak, 'stunt characters' is a common expression for the control codes: LF, CR, LTRS, FIGS and SPACE. In this case they are used to put the teleprinter in a known state. They are not part of the key.

Block diagram
The block diagram below shows how the key gun works. As the tape can be pulled through the reader at arbitrary speed, the central timing (clock) is controlled by the sprocket hole in the paper tape. The 5-bit parallel data from the tape reader is serialised (P/S) and then evaluated (EVAL).

Depending on the setting of the MODE selector on the device and/or the contents of the key tape, a 50-bit key is read from tape and stored in the selected key compartment, where it is retained by an internal battery. When the START-button is pressed, the data is transferred from the selected key compartment in memory, to the connected communication device (e.g. MSC-2001).

The key gun is housed in a strong die-cast aluminium enclosure, that is painted in a NATO olive green colour. The enclosure consists of two case shells that are held together by a hinge at the side of the connector. It can be opened by loosening the screw at the opposite side of the case.

Inside the case are two printed circuit boards (PCBs) that are mounted together in parallel like a sandwich. The PCBs are not fixed inside the enclosure but are held in place by the case shells. The image on the right shows the opened Key Gun, with the two small PCBs sticking out.

At the front edge of the PCB stack are the back­up battery – which has to be replaced every few years – and the small paper tape reader. At the left is the wiring to the large 14-pin connector. At the top right is the control panel, with the CODE selector, the START button and the LED.
Opening the device

Re-assembling the device can be troublesome, as it appears to be difficult to close the device whilst holding the two PCBs in the appropriate position. Never use excessive force when closing the device. When the device is finally closed, replace the screw that locks the two case halves.

Screw that holds the device closed Opening the device Open device with two PCBs Two sandwiched PCBs Backup battery Tape reader Cable to device with NF-7 socket
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Screw that holds the device closed
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Opening the device
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Open device with two PCBs
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Two sandwiched PCBs
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Backup battery
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Tape reader
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Cable to device with NF-7 socket

The diagram below shows the pinout of the male 14-pin connector at the front of the device, as seen from the solder side of the connector. This is the same as looking into the female socket into which it is inserted. The pinout is suitable for direct connection to the MSC-2001.

  1. System ground
  2. not connected
  3. not connected
  4. not connected
  5. Link E-F-N
  6. Link E-F-N
  7. Key input check (input)
  8. not connected
  9. (-) Reader voltage (input)
  10. Clock (output)
  11. not connected
  12. Link E-F-N
  13. Data (output)
  14. Read/write (output)
Compatible devices
The following devices are known to be compatible with the Siemens Key Gun:

  1. Helmut 'Jim' Meyer, HS0ZHK, My way to Ham - Radio and beyond
    Website QRZ.COM. Personal correspondence, December 2017.

  2. Odyssee 2001, Key Word Creation for Voice Encryption Unit, Version 2.2
    Security Technology Inc. Cheyenne, Wyoming, USA. September 1994, Rev. 1.
Further information
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Crypto Museum. Created: Tuesday 26 December 2017. Last changed: Monday, 16 September 2019 - 12:34 CET.
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