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← UK Voice Saville BID/2510 → KY-57 →
The DMU allowed speech and data to be sent at 16 Kb/s over
wide-band (8 kHz) VHF and UHF links. Secure conversations were only possible
if the BID/250 crypto module was present inside the DMU.
The crypto module replaced the blue cover plate at the center of
the DMU front panel.
Cryptographic keys were loaded into
the BID/250 by means of a standard
key-fill device, such as the
KYK-13
or the KOI-18.
Due to the fact that the BID/250 used the
SAVILLE crypto algorithm,
it was crypto compatible with
the American KY-57
(and with the later KY-99).
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The units had an extremely long life span. Although BID/250 was
introduced in the early 1970s, some
versions of it
were still in use in 2009. From 2009 onwards [2],
existing BID/250 units were gradually phased-out when
Clansman was replaced by the new
Bowman communications system.
In December 2014, BID/250/11 was replaced by the compatible
software-defined BID/2510/16.
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A complete Clansman radio station, for example as it was built inside
an FFR Land Rover, consists of a VRC-353 VHF 50 Watt radio plus a
Digital Master Unit (DSU).
The latter is actually a switch box that allows
speech and data to be routed through the (optional) BID/250. The images
below show how the rather small BID/250 is installed in the rectangular
slot at the centre of the front panel. It is locked in place by a black
hinged metal frame with a locking knob at the right.
Under normal conditions, the BID/250 unit was not installed and the blue
blanking plate that replaced it, showed that secure operation was not possible.
This was done to avoid the risk of losing the precious encryption module.
Only in actual battle missions, a crypto officer would install the BID/250
unit and load it with the appropriate keys. Once the mission was over, the
encryption unit was removed and replaced by the blue blanking plate again.
During training missions, the BID/250 was often replaced by a simulator.
It had the same size as the BID/250/1 and BID/250/11 units and allowed the
use of digital communications without providing the encryption/decryption
capabilities. The simulator is further explained below.
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The diagram below shows how the BID/250 was used.
At the right is a typical VRC-353 Clansman transceiver,
consisting of a transmitter (TX) and a receiver (RX).
The unit at the left is the Digital Master Unit (DMU),
which is in fact a switch box that can pass the analogue audio
signals straight through to the transceiver, or route them
through the (optional) BID/250 at the heart of the DMU.
Inside the BID/250, the analogue microphone signal is first
converted to a digital signal using Continuous Variable Slope Delta
modulation (CVSD). The digital signal is then encrypted with
a Cipher Text Auto Key (CTAK stream cipher),
after which the signal
is fed into the wide-band 'X' input of the transmitter.
In receiving mode, this works in reverse direction.
Due to the nature of the CTAK stream cipher, also known as CFB, 1
the crypto-unit is fully
self-synchronising.
The BID/250/1&11 Simulator consists of a metal enclosure with the
same form factor as the real BID/250. It can be installed in the DMU
instead of the BID/250 for training purposes. In this case, the digital
CVSD signal is fed directly into the wide-band input of the transceiver.
Although the result is similar as with the encryptor in place (the user
will just hear noise) the signal is not actually encrypted. During training
missions this prevented the risk of losing real BID/250 units.
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-
CFB : Ciphertext Feedback. Also known as 'Autoclave'.
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Model
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NSN
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Description
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BID/250/1
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5810-99-645-0301
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Encryption device
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BID/250/11
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7050-99-500-1818
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Encryption device (later version of the above)
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BID/250/41
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6130-99-776-9599
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Power Supply Unit
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BID/250/42
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?
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Probably another type of Power Supply Unit
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BID/250/1&11
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6625-99-633-6358
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Simulator Assembly
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BID/250/11 POUCH
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5810-99-651-7544
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Carrying bag (radio)
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BID/2510/16
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?
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Replacement for BID/250/11
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At present Crypto Museum has no BID/250 Lamberton unit in its collection,
which is why we are currently unable to show an image of it. We would very
much like to find a complete unit and/or any kind of information about
it. If you think you can help, please contact us.
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Any links shown in red are currently unavailable.
If you like the information on this website, why not make a donation?
© Crypto Museum. Created: Friday 27 February 2015. Last changed: Sunday, 25 February 2018 - 13:36 CET.
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![DSU with BID/250 simulator installed [3]](img/301555/000/thumbnail.jpg "image # 301555/000")
![Operating the BID/250 simulator [3]](img/301555/001/thumbnail.jpg "image # 301555/001")
![Close-up of the BID/250 simulator [3]](img/301555/002/thumbnail.jpg "image # 301555/002")
![DSU with BID/250 simulator installed [3]](img/301555/000/full.jpg)
![Operating the BID/250 simulator [3]](img/301555/001/full.jpg)
![Close-up of the BID/250 simulator [3]](img/301555/002/full.jpg)
