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ELCRO
Siemens
Phone
Germany
SAVILLE
STU-II
  
Elcrovox 1/3 →
  
Elcrovox 1/4
Narrow band voice and data encryptor

ELCROVOX 1/4D was a digital encryption/decryption device for voice and data communication, developed in the late 1980s by Siemens and AEG Telefunken for the German Army (Bundeswehr) and for use by NATO. The device is suitable for simplex, duplex and half-duplex at 2400 baud and features the secret SAVILLE encryption algorithm, jointly developed by GCHQ and the NSA.

The ELCROVOX 1/4D was the successor to the ELCROVOX 1/3 and ELCROVOX 1/6, and was compatible with the American STU-II and with European devices of the same class, such as the Philips Spendex 40 and the Thales TCE-500/B.

The device is suitable for secure data transfers at 2400 baud over standard 2-wire PSTN networks, and uses the NSA-developed LPC-10 vocoder for speech compression. The image on the right shows a typical ELCROVOX 1-4D terminal. At the front is a sloped control panel with a 2-line LCD display. All phone connections are at the rear.
  
Elcrovox 1-4D with CTI#1

The ELCROVOX 1/4D has full RED/BLACK separation and is fully TEMPEST proof. It complies with the STU-II standard and was approved for use by NATO (by NICSMA). About 900 units were used by the German Airforce and an unknown number by other NATO members [1]. The ELCROVOX 1-4D was succeeded in 2002 by the ELCRODAT 5-4 which is currently sold by Rohde & Schwarz [2].

Elcrovox 1-4D with smart card (CIK) Elcrovox 1-4D with CTI#1 Smart card reder (CIK) and FILL connector Power switch and display Elcrovox 1-4D front panel Elcrovox 1-4D rear panel RED connections BLACK connection
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Elcrovox 1-4D with smart card (CIK)
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Elcrovox 1-4D with CTI#1
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Smart card reder (CIK) and FILL connector
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Power switch and display
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Elcrovox 1-4D front panel
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Elcrovox 1-4D rear panel
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RED connections
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BLACK connection

History
The first narrow band speech encryption system developed by Siemens, was the ELCROVOX 1/3. It was introduced in 1968 and allowed digitally encrypted speech to be sent at speeds up to 2400 baud, using a 4-wire analogue PSTN telephone line. The ELCROVOX 1/3 was used by the German Army and by NATO, and provided good security. Communication with the American Army was not possible, as the ELCROVOX 1/3 used a proprietary algorithm which was not STU-II compatible.

In 1983, the US proposed to give 360 STU-II units on loan, but the offer was declined as the German Government decided to develop the ELCROVOX 1/4. This was possible because of a new bi-lateral agreement with the US for the development of STU-II compatible products [3].

Development of the ELCROVOX 1-4 started in 1986/87 and took several years. In order to be compatible with the existing STU-II, the device needed to have an LPC-10 vocoder, which was implemented in a Texas Instruments DSP, similar to the one that was later used in the STU-III.
  
Elcrovox 1/3. Photograph courtesy Museumstiftung Post und Telekommunikation

Furthermore, the ELCROVOX had to support SAVILLE, a high-end secret encryption algorithm jointly developed by GCHQ and the NSA in the late 1960s. Initially, the Siemens developers had implemented the algorithm in firmware using a so-called bit-slicing processor, but this design was turned down by the NSA who disapproved any firmware-based implementation of SAVILLE. Siemens then developed a dedicated chip, in the same way as Philips had done with Spendex 40.


Interior
The ELCROVOX 1-4 is housed in a heavy die-cast aluminium enclosure that measures roughly 33 x 35 x 9 cm. It can be placed at a table top and has all controls at the front on a sloped control panel. All connections are at the rear. A suitable telephone set can be placed on top of it.

The case is highly compartimented in order to provide optimum TEMPEST shielding, and the top and bottom panels even contain metal gaskets in order to avoid any unwanted eminations. The case can be divided into a top half and a bottom half. There are 8 compartments in the top half and 5 at the bottom, accomodating a total of 13 printed circuit boards (PCBs), plus the PSU. 1


The image above shows the location of each of the PCBs. As the device has full RED/BLACK separation, there are two independent power supply units, one for the RED side and one for the BLACK side, each with their own filtering. The BLACK parts are all at the top, whilst the RED parts are at the bottom. For this reason, the crypto board and the vocoders are also at the bottom.

  1. PSU = Power Supply Unit.

CTI #1
Once the Elcrovox 1/4D is properly initialized and a valid key has been loaded, a secure telephone call can be set up. Placing a call is possible via the Crypto Telephone Instrument (CTI) shown in the image on the right.

The CTI is in fact a standard telephone set from Telefonbau und Normalzeit GmbH (TN), which has been modified with extra keys and LEDs. It is connected to the CTI-1 socket of the Elcrovox 1/4 by means of a 25-way male D-connector. There was also a version with a 15-way plug.
  
CTI #1 Crypto Telephone Instrument

CTI #1 Crypto Telephone Instrument CTI #1 with cable and connector Top view of the CTI #1 Handset OFF-HOOK Operating the PTT in half-duplex mode Close-up of the indicator lights Selecting the required MODE Dialing a number
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CTI #1 Crypto Telephone Instrument
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CTI #1 with cable and connector
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Top view of the CTI #1
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Handset OFF-HOOK
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Operating the PTT in half-duplex mode
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Close-up of the indicator lights
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Selecting the required MODE
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Dialing a number

ELCRO Family
The Elcrovox 1/4 was part of the ELCRO family of devices that started life in the 1960s. For the ELCRO family, a specific cryptographic unit was developed by Siemens, which was known as ELCRO-LOGIC, although some systems, such as the ELCROVOX 1/4, supported other algorithms as well. The ELCRO-family consisted of the following product groups:

  • ELCROVOX
    Voice encryption
  • ELCROTEL
    Text encryption (digital telegraphy)
  • ELCROBIT
  • ELCRODAT
    Voice and data encryption
  • ELCROMUX
    Bulk encryption
  • ELCROLAN
    IP-based network encryption
The ELCROVOX family was initially developed by Siemens and partly by Telefunken in Backnang, which was a joint venture between Siemens and AEG. The part of Telefunken that was responsible for this development was later renamed to ANT, which is why this name may also appear on some of the equipment. In the early 2000s, development and marketing of the ELCRO range of devices was taken over by Rohde & Schwarz (R&S) in München (Munich, Germany).


Manufacturers
Over the years, the Elcrovox family was manufactured and sold by the following companies:

Interoperability
The Ecrovox 1/4 is interoperable with the following devices:

Glossary
CTI   Crypto Telephone Instrument
Standard telephone set with extra features to allow switching between plain and crypto voice. Extra TEMPEST measures are also in place.
SAVILLE   Highly secret encryption algorithm, jointly developed by GCHQ (UK) and the NSA (USA) in the late 1960s, and used by NATO.  More
References
  1. Joachim Beckh, Blitz & Anker, Band 2: Informationstechnik...
    ISBN 3-8334-2997-6. pp. 292-293.

  2. Rohde & Schwarz, ELCRODAT 5-4 Datasheet
    February 2012. Retrieved August 2013.

  3. The Joint Chiefs of Staff, Memorandum for Record
    WINTEX 83 First Impressions Conference, 22 March 1983.
    Declassified 14 December 2012, EO 13526.
Further information
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Crypto Museum. Created: Thursday 08 August 2013. Last changed: Tuesday, 27 March 2018 - 07:09 CET.
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