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OTT cipher machine (mixer) - wanted item

The ME-640 was an off-line cipher machine for teleprinter networks (telex) developed by Mils Elektronik in Mils (Austria) in 1986, as the successor to the ME-840. The machine offers unbreakable encryption, using One-Time Tapes (OTT), as well as algorithm-based encryption.

The image on the right shows a typical ME-640 machine. It has an optical punched paper tape reader at the top left, through which the pre-generated key tape is fed from the right. In OTT-mode, the machine accepts any type of random key tape. Such tapes are typically generated by an old A-6723 key puncher or a new ME-600.

If no random key tape is available, the ME-640 can always fall back to its built-in, non linear, microprocessor-controlled, electronic key generator. Although less secure, it offers very strong encryption with 3 different key levels.


Key Generator
When using the internal key generator, the following three levels of cryptovariables are available:

  1. Long Term Key
    Permutation Key: 8.6 x 10506 settings
    Algorithm Key: 1.2 x 1024 (telex), or 3.4 x 1038 (ASCII)

  2. Secret Key
    7.9 x 1028 settings

  3. Message Key
    1.1 x 1015 settings (telex applications)
    1.2 x 1024 settings (ASCII applications)
Help required
At present we have no further information about this device. Furthermore, we are still hoping to add it to our collection in due course. If you have such a device or any related information, and are willing to donate it to Crypto Museum, please contact us.

  1. Mils Elektronik, ME-640 Off-Line Telex Cipher System
    User Manual (English). 14 pages. Date unknown, but probably 1986. 1
  1. Document kindly supplied by Mils Electronic.

Further information
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Crypto Museum. Created: Friday 28 August 2015. Last changed: Saturday, 24 February 2018 - 13:36 CET.
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