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Encrypted teletypewriter

T-1000/CA was an online/offline cipher machine for teleprinter traffic (telex) developed between 1976 and 1982 by Siemens in München (Germany) in cooperation with philips Usfa in Eindhoven (Netherlands). The device was intended for use by civil and non-NATO military users. A more secure NATO-approved version of the device was sold by Philips Usfa under the name Aroflex.

As the name suggests, the T-1000/CA is based on the Siemens T-1000 electronic tele­type­writer, that is modified and improved for Crypto­graphic Application (CA). The actual Crypto Module was made by Philips and was bolted to the bottom of the machine, as shown in the image on the right.

Although the Crypto Module is largely identical to that of the Philips Aroflex – with the Crypto Heart in a potted confidential package – it uses a different – less secure – cryptographic algorithm. As a result, Siemens was allowed to sell the machine to countries outside the NATO sphere.

 Philips Aroflex


In order to allow Siemens to sell the civil version of th Aroflex, Philips supplied the bare Crypto Module to Siemens. In this case, the combination was called T-1000/CA, in which the extension CA stands for Cryptographical Application. This variant was not sold to NATO customers.

In Jane's Military Communication, edition 1986, Siemens offers the machine as the T-1000/CA, with a black (rather than cream) body stowed in a matching flight-case [1]. According to an internal Philips memo [2], just one batch of 1500 crypto add-on modules was made for Siemens.

Note that the Siemens T-1000/CA is electrically identical to the standard Philips Aroflex, but that the actual cryptoheart is different. The one in the T-1000/CA is built around OQ4407 custom chips, whereas the Philips variant (that was used by NATO) contains the pin-compatible OQ4406.

The image above shows the interior of the Siemens crypto heart that was based on the OQ4407. The algorithm of the OQ4407 (and hence the Siemens T-1000CA) is substantially weaker than that of the OQ4406 and could be broken with the right means, exploiting the redundancy in the encyphered message preamble. This would typically involve solving a set of binary equations, an exponentially large number of times, a task that was not trivial at the time.

Rumour has it that Philips designed and developed a special chip to speed up the analysis of OQ4407-based crypto-logics upon request of the Dutch authorities. The cryptograms produced by the T-1000CA machines, typically exhibit bias in the enciphered message preamble, an un­necessary shortcoming by design. This was certainly known by the agencies of other countries.

Also note that the crypto-logic with the OQ4407 had two 16-pin connectors by which it was connected to the mixer board, whereas the real Aroflex crypto-logic with the OQ4406 had only one such connector. The same is true for the mixer board. It is therefore possible to identify the chips inside the crypto-logic without opening them. One cable: OQ4406, two cables: OQ4407.

  1. Jane's Military Communication 1986
    ISBN: 0-7106-0824-1

  2. Philips Usfa, Internal Memo L/5636/AvdP/JG
    23 August 1982, page 5.
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Crypto Museum. Created: Monday 19 August 2019. Last changed: Saturday, 04 January 2020 - 13:32 CET.
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