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Bosch KF-802   FuG-8b
Two-way FM/PM VHF radio

KF-802 was an analogue two-way VHF mobile radio set, introduced in 1978 by Bosch Telecom in Gerlingen (Germany). It was developed for use by German public safety services (BOS), such as the police and the fire brigade, in compliance with the German Government's FuG-8 specicification. In 1983, optional voice encryption was added. The radio is commonly known as Bosch FuG-8b [1].

The FuG-8 was made by various manufacturers, including SEL, Bosch and AEG Telefunken. The dimensions of the enclosure and the layout of the front panel was dictated by the government specification, but internally the devices were completely different. The image on the right shows the Bosch FuG-8b-1, which has an extra voice security unit bolted-on at the bottom.

In this particular variant, the Bosch FuG-8 offers two methods for protecting speech: a rather sophisticated time domain scrambler made by BBC, and a much simpler frequency inverter.
  
Bosch FuG-8 (KF-802) with integrated Vericrypt 1100 voice scrambler

Speech scramblers were very popular during the 1980s with government organisation such as the police, for protection against occasional eavesdroppers. They are by no means secure, but offer reasonable protection, and have the advantage that they work within the existing (analogue) voice spectrum. This means that they could be added to an existing radio without altering any circuits.

The FuG-8b-1 shown here, was introduced around 1983, and had an extra 'blob' at the bottom, that was intended for the (optional) voice scrambler. It has two extra switches: one to toggle between clear and secure, and one for selecting the desired voice scrambling method.

By default, the radio uses the internal Vericrypt 1100 scrambler, made by the Swiss company Brown Bovery (BBC). This time domain scrambler, mixes the order of a finite number of speech fragments in an ever changing order, controlled by an internal pseudo-random key generator.
  
Bosch FuG-8 with (optional) voice scrambler bolted-on at the bottom

The key generator is initialised, or seeded, by a user-configurable cryptographic key, that is loaded into the device by means of a key loader or filler, that can be connected to a 5-pin LEMO socket on the front panel. In normal use, this socket is covered by a protective rubber cap.

In order to allow secure voice communication between the various parties, all mobile radios and base stations have to be loaded with the same cryptographic key. This means that the keys have to be distributed prior to the session.

If one of the parties does not have the required key, all parties have to turn off the scrambler in order to resume the conversation, making it prone to interception. As a last resort, the FuG-8 shown here, also has a simple retrofitted speech inverter with a fixed mirroring frequency, that could be selected as an emergency alternative.
  
Bosch FuG-8 (KF-802) with built-in Vericrypt 1100 voice scrambler and key entry device

A frequency inverter is the simplest form of a frequency domain speech scrambler and offers very little security. in the 1980s, many hobbyist scanner listeners used a simple frequency inverter to make the conversation audible again. Nevertheless, it is better than using no protection at all, if the regular (Verycript 1100) method is not available. The simple frequency inverter was probably developed by Bosch, and was introduced in the early 1990s as a mid-life upgrade. It is known as SVZ and is based on a single-chip solution, much like the Bosch SVZ-8/9, but less sophisticated.

 More about the SVZ speech inverter

Bosch FuG-8 (KF-802) with integrated Vericrypt 1100 voice scrambler Bosch FuG-8 with (optional) voice scrambler bolted-on at the bottom Controls and socket on the scrambler unit Lifting the rubber cap Bosch FuG-8 (KF-802) with built-in Vericrypt 1100 voice scrambler and key entry device Key filler connected to the FuG-8 Key filler connected to the LEMO socket Key filler attached to the LEMO socket at the front of the FuG-8
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Bosch FuG-8 (KF-802) with integrated Vericrypt 1100 voice scrambler
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Bosch FuG-8 with (optional) voice scrambler bolted-on at the bottom
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Controls and socket on the scrambler unit
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Lifting the rubber cap
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Bosch FuG-8 (KF-802) with built-in Vericrypt 1100 voice scrambler and key entry device
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Key filler connected to the FuG-8
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Key filler connected to the LEMO socket
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Key filler attached to the LEMO socket at the front of the FuG-8

Interior of the speech scrambler extension

Interior
The scrambler extension, bolted-on at the bottom of the basic KF-802 (FuG-8) radio, can be opened by releasing four large bolts in the corners of the bottom panel, after which the bottom panel can be removed. The diagram above shows the interior of the speech scrambler extension.

It consists of a carrier board that holds the extra modules and connections. At the left is a metal unit, that contains an FMS identifier, made by RDN Radiodata GmbH. At the right is space for the BBC Vericrypt 1100 unit that is plugged into a 25-way sub-D socket on the carrier board. It was supplied by Brown Boveri as an OEM unit.

At the right, close to the front end of the case, is a small PCB that carries the simple Bosch SVZ frequency inverter, that was added as a retrofit solution in the early 1990s. For this addition, an extra toggle switch was added to the front panel.
  
Location of the various parts

The extra switch allows the user to select between the BBC Vericrypt 1100 and the Bosch SVZ. With the leftmost switch on the front panel, speech scrambling can be switched OFF altogether. Note that the security offered by the Vericrypt is much better than that of the SVZ. Nevertheless, speech scramblers, no matter how complex, are inherently insecure and can easily be broken.

 More about the BBC Vericrypt 1100
 More about the Bosch SVZ

Interior of the scrambler unit Bottom view Identification unit Embedded Vericrypt 1100 module Simple frequency inverter with limited security Cabling and switches Location of the various parts Label on the Vericrypt module
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Interior of the scrambler unit
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Bottom view
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Identification unit
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Embedded Vericrypt 1100 module
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Simple frequency inverter with limited security
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Cabling and switches
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Location of the various parts
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Label on the Vericrypt module

Data terminal
In Germany, the police also used the FuG-8b for sending digital text-based messages through the air, in order to interrogate the so-called INPOL database. INPOL contained information about car registrations, people, criminal records, suspects, terrorism, etc.

Especially for this application, AEG Telefunken developed the Telestar text terminal shown in the image on the right. It had a full-size keyboard and a built-in thermal printer.

 More information
  
Telefunken Telestar 121


Connections
Handset
At the left side of the control unit is a 7-pin U-79U socket, that accepts a standard NATO 7-pin U-77 plug with the following pinout:

  1. n.c.
  2. PTT
  3. PTT
  4. Speaker
  5. Speaker
  6. Microphone
  7. Microphone
  8. Ground
Rear connector
  1. 12.6V
  2. 12.6V
  3. 12.6V
  4. n.c.
  5. 0V (battery ground)
  6. 0V (battery ground)
  7. 0V (battery ground)
  8. Ruf 1 (1750 Hz)
  9. Wandler - Ein
  10. Wandler - Ein
  11. NFL
  12. Ground
  13. NFLR

  14. Ein
  15. Ruf 2 (2135 Hz)
  16. NF- Ein
  17. n.c.
  18. A: Empfangsanzeige RSP
  19. B: +11.6V (UST)
  20. C: PTT
  21. D: Speaker (ground)
  22. E: Speaker (signal)
  23. F: Microphone (ground)
  24. H: Microphone (signal)
  25. J: Ground
References
  1. Klaus Paffenholz, Bosch FuG 8a / 8b / 8a-1 / 8b-1 (KF-802)
    Website: Geschichliche Entwicklung des BOS-Funks (German).
    Retrieved June 2017.
Further information
Key filler connected to the FuG-8
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Crypto Museum. Created: Thursday 29 June 2017. Last changed: Tuesday, 01 August 2017 - 14:05 CET.
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