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Voice Telsey TDS-2004 → TDS-2003 →
The image on the right shows the front panel of a typical TS-500 unit.
It only has one switch, that is used to select between CLEAR and encrypted
voice (CRYPTO). No other controls are present.
The scrambling sequence is controlled by the encryption key, which is
implemented as a small printed circuit board (PCB) with a fixed wiring
maze or labyrinth. This key card must be inserted into a slot
at the front panel of the device. The tracks at both sides of the card
are identical, allowing it to be inserted either way.
Both ends should used identical key cards.
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The TS-500 was introduced in 1976, and was the company's first secure voice
product after its foundation in 1971. It was
developed by Oscar Steila shortly after he had joined the company.
Steila would later become the managing director of Telsy.
The TS-500 was succeeded in 1978 by the TDS-2000
series duplex voice encryption devices that offered 2-dimensional
scrambling.
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The key space of the TS-500 is very limited. There are just 10
contacts at either side of the key card but only one side is actually used.
Of the 10 contacts, only 9 are wired.
If we assume that there must be at least one common line (GND),
8 contacts are available for creating a key.
This results in 28 = 256 possibilities.
These can easily be checked with an exhaustive search.
Furthermore, the card can easily be duplicated by simply making a
photograph and following the tracks.
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Despite the simplicity of the key card, the actual electronics
are rather advanced considering the unit's age.
The TS-500 contains two PCBs that are easily revealed by removing the
cover. They are mounted back-to-back, so that the components are
immediately visible. The Logic Board
contains all digital components, whilst the
Audio Board contains the analog components.
At the heart of the system are two FX-209
Adaptive Delta Modulation chips,
manufactured by CML in the UK. One is used as an encoder, whilst the other
one is the decoder. Analog speech is digitized with a delta demodulator,
after which it is scrambled in the time domain and converted back into
an analogue signal by means of a delta modulator.
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© Crypto Museum. Created: Friday 14 September 2012. Last changed: Wednesday, 21 August 2024 - 09:13 CET.
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