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Elcrovox 1/3
Narrowband voice encryptor - this page is a stub

Elcrovox 1/3 is a high-end military voice encryption device, developed around 1972 by Siemens in München (Munich, Germany) for use by the German Army (Bundeswehr) and by NATO. It uses a proprietary encryption algorithm and was succeeded in the late 1980s by the Elcrovox 1/4.

The device is approx. 19" wide and is housed in an olive green aluminium transport case, from within it is operated. Controls and connections are at the front. At the centre is a locked hinged door behind which the KEY material is installed.

The image on the right shows an typical Elcrovox 1/3, from the collection of the Museum for Tele­communication in Frankfurt (Germany) [1]. The device was used in many NATO countries, such as Germany, the Netherlands and also in Canada. According to the US, it's quality was comparable to the NSA-developed STU-II voice encryptor [3].
  
Elcrovox 1/3. Photograph courtesy Museumstiftung Post und Telekommunikation [1].

The problem with the Elcrovox 1/3 however, is that it is not interoperable with the STU-II and other voice encryption products that use the secret NSA/GCHQ encryption algorithm SAVILLE, which limits its usability. This problem was solved in March 1983, with a bi-lateral arrangement, that allowed Germany to develop its own STU-II compatible products, just like Philips Usfa had done a few years earlier [3]. It resulted in the development of the backwards compatible Elcrovox 1/4 which was fully interoperable with the STU-II and compatible products like the Spendex-40.


Key entry
Before the Elcrovox can be used, a suitable key has to be installed in the device. This is done by placing two pieces of punched paper tape in the tape reader, or scanner, that is present behind a locked door at the centre of the device. The two paper strips are prepaired in advanced by the German BSI, and contain the cryptographic key. In practice, the key was renewed every 24 hours.

The two pieces of punched paper tape are first installed in the so-called key block, which is a spring-loaded metal bracket in which one tape is installed at either side. It is held in place by a hinged metal frame. At the center of the key block are 32 copper-plated springs that are all connected to the electric ground. Two metal pins at the center are for aligning the punched tape.

As the key block accepts 5-level paper tape and has 32 spring positions, it is likely that each side of the key block specifies 32 5-bit characters, which implies a possible key length of 320 bits.
  
Frame open for installation key tape

The image above shows the rectangular key block with both hinged frames open, ready to accept two key tapes. The frames are marked part 1 and part 2 respectively, corresponding to the two paper tapes. The key block measures approx. 110 x 38 x 21 mm (without the cap at the front). The Elcrovox 1/3 was usually supplied with a minimum of two key blocks, so that one could be prepaired for the next key, whilst the other one was in use. At midnight the blocks were swapped.

Once both punched paper strips are in place, the two hinged frames are closed and the key block is inserted into the reader at the centre of the Elcrovox, as shown in the image on the right.

When the block is fully pushed-in, it is locked in place by a spring loaded catch. At the same time the two sides of the block are pushed sideways by a cleverly made spring-loaded mechanism. This brings the tape in contact with five rows of tiny spring-loaded contacts. Whenever a hole is present in the key tape, it is protruded by one of the spring-loaded pins, which is then grounded.
  
Key block with key tape half-way inserted

The presence and absence of holes in the key tape, represent the individual bits of the key, that are stored in the latching circuit on the four printed circuit boards that surround the tape reader. The key bits are then used as the seed or initialisation vector of the internal (probably non-linear) pseudo random number generator (PRNG), that generates a key stream with a, extremely long cipher period. The latter means that it takes a long time before the key sequence repeates itself.

Elcrovox 1/3 key tape reader Key tape reader with two inserts Two tape inserts Key tape insert Frame open for installation key tape Two tape inserts Inserting the key tape unit Key tape unit fully inserted
Close-up of the (ground) contact springs One side of the key block, with hinged frame open. Key tape insert (unexpanded) Key tape insert (expanded) Tape reader seen from the front/side Spring loaded contact pins at either side of the slot Key block with key tape installed Close-up of installed key tape. Note the two alignment pins at the centre.
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Elcrovox 1/3 key tape reader
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Key tape reader with two inserts
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Two tape inserts
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Key tape insert
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Frame open for installation key tape
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Two tape inserts
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Inserting the key tape unit
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Key tape unit fully inserted
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Close-up of the (ground) contact springs
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One side of the key block, with hinged frame open.
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Key tape insert (unexpanded)
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Key tape insert (expanded)
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Tape reader seen from the front/side
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Spring loaded contact pins at either side of the slot
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Key block with key tape installed
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Close-up of installed key tape. Note the two alignment pins at the centre.

Test device 1
Several test devices were available for testing the performance of the Elcrovox 1/3 and for finding faults in its operation. The image on the right shows Test Device 1 (German: Prüfgerät 1), that can be connected directly to the Elcrovox 1/3.

The device consists of a small junction box with a standard 10-pin NATO headset, plus a short cable with a 19-pin and an a 41-pin plug at the end. Furthermore, a 10-pin loop connector is attached with a chain to the 41-pin plug.
  
Prüfgerät 1 for Elcrovox 1/3

Test device 2
The image on the right shows Test Device 2 (German: Prüfgerät 2), that can be connected directly to the Elcrovox 1/3 via three 1 metre long patch cables. The device was used for testing the performance of the Elcrovox 1/3 and for finding faults in its operation.

The device comes with four test cards that are stored behind the hinged door at the right. These cards are intended to replace specific cards inside the Elcrovox 1/3 during the test.
  
Prüfgerät 2 (test device 2) for Elcrovox 1/3

Test tapes
Especially for testing the functionaly of the Elcrovox 1/3 and for discovering faults in its crypto functions, a series of test tapes were issued. The image on the right shows a set of test keys tapes for the Elcrotel 4 cipher machine, that are also suitable for the Elcrovox 1/3.

The set consists of three bundles of short red and blue test tapes, marked TEST 01 (a real key), TEST 02 (all holes) and TEST 03 (no holes). The yellow tapes are not used on the Elcrovox 1/3.
  
Siemens test tapes

Prüfgerät 1 for Elcrovox 1/3 Prüfgerät 1 Plugs on Test Device 1 41-pin interconnection cable 19-pin interconnection cable 10-pin interconnection cable Junction box and calibration cable Test Device 2 with test cables connected
With cover closed With from cover removed Prüfgerät 2 (test device 2) for Elcrovox 1/3 Front view Front panel Opening the hinged lid Test cards stored behind hinged lid Instructions inside front cover
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Prüfgerät 1 for Elcrovox 1/3
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Prüfgerät 1
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Plugs on Test Device 1
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41-pin interconnection cable
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19-pin interconnection cable
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10-pin interconnection cable
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Junction box and calibration cable
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Test Device 2 with test cables connected
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With cover closed
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With from cover removed
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Prüfgerät 2 (test device 2) for Elcrovox 1/3
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Front view
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Front panel
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Opening the hinged lid
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Test cards stored behind hinged lid
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Instructions inside front cover

Spare parts
In order to allow quick and efficient repair of an Elcrovox 1/3 unit in the field, a collection of spare parts was supplied to countries that used the device. The spare parts were usually supplied in a large aluminium transport case.

With the exception of the actual cipher unit (also known as the crypto logic), a broken device could be repaired within minutes, simply by swapping the defective module. Repairs to the crypto logic were only carried out by Siemens.
  
(1) Elcrovox 1/3 PSU

(1) Elcrovox 1/3 PSU (2) KV4-2A/40 interface Interface (3) 15V regulator (5) 1V regulator (6) 12V regulator (7) 12V regulator (8) Elcrovox 1/3 PSU
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(1) Elcrovox 1/3 PSU
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(2) KV4-2A/40 interface
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Interface
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(3) 15V regulator
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(5) 1V regulator
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(6) 12V regulator
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(7) 12V regulator
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(8) Elcrovox 1/3 PSU

Help wanted
At present, no further information about the Elcrovox 1/3 is available. You can help expand this page by providing additional information and material. For contributions, please contact us.


References
  1. Museumsiftung Post und Telekommunikation, Image of Elcrovox 1/3
    Frankfurt (Germany). Retrieved September 2017.

  2. Anonymous, Prüfgerät 2 für Elcrovox 1/3 - THANKS !
    Elcrovox 1/3 Test Device 2. September 2017.

  3. The Joint Chiefs of Staff, Memorandum for Record
    WINTEX 83 First Impressions Conference, 22 March 1983.
    Declassified 14 December 2012, EO 13526.
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© Crypto Museum. Created: Thursday 21 September 2017. Last changed: Tuesday, 27 March 2018 - 07:10 CET.
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