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Siemens DSM Voice
Telephone voice encryptor

Data Security Module (DSM) Voice is a digital encryptor for analogue telephone lines, developed around 1996 by Siemens in Munich (Germany). The DSM Voice is connected between the regular analogue telephone set and the analogue network (POTS). It uses a smart card for authentication.

The unit is normally placed aside or under the telephone set. At the rear are sockets for the phone, the line and the external power supply unit (PSU). The control panel consists of an LCD display, 3 LEDs and a single push-button.

The slot above the display accepts a smart card, as shown here. It is used for authentication and public key exchange (PKE). Insert the card and press the button on the control panel, to enter secure mode (crypto). Call partner authentication is performed automatically, and for each call, a new session key will be generated by the device.
Siemens DSM Voice with chip card

MRCELP vocoder technology is used to provide good quality speech in encrypted mode. The DSM Voice is only suitable for speech (voice) at it uses a lossy compression technique. Alternative DSM units were available for other types of data, such as DSM Fax, DSM X.25, DSM Link and DSM ISDN [2]. At present, no further information about these units is available. If you know more about the Siemens DSM family of devices, or if you happen to have user manuals, please let us know.

Control panel Smart card and DSM Voice unit DSM Voice unit and smart card Inserting the smart card DSM Voice unit with smart card present Siemens DSM Voice with chip card Connections at the rear DSM Voice with PSU
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Control panel
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Smart card and DSM Voice unit
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DSM Voice unit and smart card
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Inserting the smart card
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DSM Voice unit with smart card present
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Siemens DSM Voice with chip card
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Connections at the rear
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DSM Voice with PSU

The following DSM family members are known:

  • DSM Voice
  • DSM Fax
  • DSM X.25
  • DSM Link
ISDN   Integrated Services Digital Network
Digital telephone standard that was intended to replace the analogue POTS system, but that has since been superceeded by IP-telephony.
MRCELP   Modified Residual Code Exited Linear Prediction
High-quality low-bitrate speech digitiser, used for encrypted voice connections over regluar analogue lines. Improved variant of MELP and MELPe, that produces better results at 9600 baud.
POTS   Plain Old Telephone System
Old analogue telephone system.
  1. Barry Wels, Siemens DSM Voice unit - THANKS !
    Crypto Museum, February 2011.

  2. Jane's Military Communications 1997-98
    ISBN: 0-7106-1530-2. p. 532
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Crypto Museum. Created: Wednesday 06 February 2013. Last changed: Friday, 18 January 2019 - 20:14 CET.
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