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← TST Data
Data encryptor with HF-modem and FEC
The TST-4043 was a small military-grade data encryption/decryption unit
with built-in HF radio modem and advanced Forward Error Correction (FEC),
developed and built around 1984 by Tele Security Timmann (TST)
in Pöcking (Germany). It was intended for use by Military and Diplomatic Services
world-wide. The initial version was housed in metal case with dangerously
sharp edges.
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A later version, shown here, was housed
in a typical modular case that was also used for
a number of other TST products
(e.g. TST-7700).
The unit is powered directly from the (220V) AC mains and allows
a teleprinter,
using the Baudot standard, or a computer, using the
7/8-bit ASCII standard,
to be connected directly to an HF radio by means
of the built-in AFSK modem [A].
The device was mainly intended for sending messages over relatively slow
and noisy HF radio channels, such as the short-wave bands [A].
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For many years HF radio was used for communication with embassies.
The TST-4043 contains three basic functions that ensure a reliable and
secure connection: (1) A high-end AFSK radio modem, (2) advanced suppression
of errors, using Forward Error Correction (FEC) and (3) a built-in high-end
data encryption device. The device supports data transfer rates between
75 and 300 baud and the FEC improves the reliability by a factor of 1000
or more on bad (noisy) channels.
The TST-4043 does not have any controls on its front panel. Instead it
is fully controlled from the terminal connected to it (i.e. the teleprinter
or the ASCII computer terminal). Cryptographic keys are loaded via the
same terminal and do not require the use of a dedicated key loading
device.
The 25-way D-type connector at the front, holds all signals that are
necessary for the connection of a terminal. It has a full RS-232
interface for the connection of a computer or an ASCII terminal.
5-Bit teleprinters
can be connected with either 20 mA or 40 mA,
single current or double current.
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The interior of the TST-4043 can easily be accessed by either removing
the front panel or the rear panel, by releasing the bolts in the four
corners. As nothing is attached to the front panel, it is probably the
easiest to get access via the rear, after which
three units become visible.
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Looking inside the device from the rear,
we see (from right to left) the mains power supply,
the encryption board
and the interface board.
The encryption board is built around a National Semiconductor
NSC 800 processor,
the military variant of the Zilog Z-80. The board contains
(volatile) static RAM on which the cryptographic keys are kept by means
of a Lithium battery.
At the bottom right are eight DIP-switches
that can be used to alter the configurations of the device
(the settings are currently unknown).
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The other PCB contains the HF modem and the line interface transformers.
The text has been removed from the AFSK modem chips, something that was
frequently done in those years to protect the design. At the top right
is a temperature controlled 2.4576 MHz oscillator.
The encryption/decryption board was also available separately for
OEM applications as the TST-9669.
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© Crypto Museum. Created: Sunday 14 July 2013. Last changed: Tuesday, 27 February 2018 - 13:47 CET.
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