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Ecolex Mark 2
One-Time Tape cipher machine - wanted item

Ecolex Mark 2 is an online/offline One-Time Tape (OTT) cipher machine for teleprinter circuits, developed around 1953 by the Dutch Post Office (PTT). It was never taken into production, but was succeeded by a fully transistorised version, which was initially known as Ecolex Mark II B. The latter was produced until 1963 by Philips Usfa in Eindhoven (Netherlands) as the Ecolex II.

Two versions 1 of the Ecolex I existed: Mark 1, which operated on the 26 characters of the Latin alphabet and was compatible with existing mechanical OTT machines, and Mark 2, which operated on all 32 characters of the ITA2 tele­graph alphabet. [B] The image on the right shows the Ecolex I Mark 2 without its cover. It is believed to be the only surviving specimen of this model, and is currently held in an internal collection of the Dutch Department of Defense.

The machine is built around 22 switching elements and 250 rectifier cells (diodes).
  
Ecolex I Mark 2

The switching elements are implemented as circular plug-in units with an E90CC special quality (SQ) double-tetrode valve on top. At the rear are the transformers and a cooling fan. The device is much simpler than its bigger brother, the Ecolex I Mark 1, which operates on the 26 characters of the Latin alphabet only, and consists of no less than 68 switching elements and 600 diodes.

The Ecolex I Mark II had PTT model number 3201 and was produced in a small prototype series. The unit shown above has serial number 102. If we assume that numbering started at 100, this means that it is the second prototype. No further 3201 units were made, as the next prototype – 3202 – was built with transistors [9]. After a few protypes made by PTT, production of the fully transistorised version was taken over by Philips Usfa, where it was known as US 8011 or Ecolex II.

 More about the Ecolex I Mark 1
 More about the Ecolex II

  1. The suffix 'I' (one) to the model name Ecolex I was added once the development of the Ecolex II had started. Before that time, the device was simply known as Ecolex. The two versions were known as Mark 1 and Mark 2, which, confusingly, was also written as Mark I and Mark II.

Ecolex I Mark 2
Ecolex I Mark 2
Left angle view
Rear view
Connections at the rear
Right side view
Left side view
E90CC valves
A
×
A
1 / 8
Ecolex I Mark 2
A
2 / 8
Ecolex I Mark 2
A
3 / 8
Left angle view
A
4 / 8
Rear view
A
5 / 8
Connections at the rear
A
6 / 8
Right side view
A
7 / 8
Left side view
A
8 / 8
E90CC valves

Principle
One-time tape machines like the Ecolex I are in theory unbreakable if, and only if, the keystream tape is truly random, the tape is used only once, and the tape is destroyed immediately after use. In the machine, plaintext (from the teleprinter or the first tape reader) is added to the random tokens from the second tape reader by means of modulo-2 addition, also known as exclusive-OR (XOR). This principle, invented in 1970 by Gilbert Vernam, is known as the Vernam Cipher. The process is also known as mixing, which is why OTT machines are also known as mixers.

Modulo-2 addition of the characters from two tapes

The advantage of using modulo-2 addition (XOR) is that the same procedure can be used with the ciphertext to reveal the plaintext. The process of unmixing is identical to the process of mixing.

 More about the Vernam Cipher


Key tapes
For generation of the keytapes it is important that it contains truly random characters, which is why they are also known as noise tapes. In practice however, many governments created the key tapes with a pseudo-random number generator (PRNG), which is much weaker, as in that case the 'noise' is deterministic. For this reason, PTT developed its own random noise generator: EROLET.

 More about the EROLET keytape generator


Equipment
Ecolex I Mark 1
The image on the right shows a complete setup with the Ecolex I Mark 1. The machine itself is at the far right. At the left is a Siemens T-37 tele­printer which is used as an input/output device. At the centre is a Siemens T-send-77f double tape reader on which the plaintext and the key stream tape are loaded. The large Power Supply Unit (PSU) is hidden under the table.

The machine is built around 68 valve-based switching circuits and 600 rectifier cells (diodes).

 More information

  
Complete setup (without the PSU)

Ecolex I Mark 2
The Ecolex I Mark 2 is much smaller than the Mark 1, and works on any of the 32 characters of the ITA2 telegraph alphabet. Contrary to the Mark 1 however, the Mark 2 is only suitable for point-to-point traffic, in which an identical machine is used at both ends.

The device consists of 22 switching circuits built with E90CC valves and 25 rectifier cells (diodes). It is likely that the machine shown in the image on the right is the only surviving specimen. The machine described on this page is of this type.

  
Ecolex I Mark 2

Double tape reader   T-send-77
Regardless the version, a double punched paper tape reader had to be connected to the dive, so that plaintext and keystream could be read simultaneously and mixed in the Ecolex.

The image on the right shows (a variant) of the Siemens T-send-77, which had been developed especially for this purpose. It was also used with other cipher equipment like Schlüsselgerät D, a similar OTT machine made by Siemens.
  
Siemens T-send-77b



History
WWII
In the years following WWII, the countries of the Western Union (WU) had a growing need for secure military and diplomatic communications equipment. After the WU had been dissolved into the newly established NATO (1949), the need for secure communication became even more important. Initially, only the British 5-UCO, a left-over from WWII, was available for this, but the British were unable to supply it in sufficient quantities to fulfill the needs. Apart from that, the 5-UCO was a rack-based solution that was way too large to be of any practical use in the field.

In 1953, the Norwegian company STK tried to fill the gap by developing the ETCRRM, a valve-based OTT machine that was much smaller than the 5-UCO and easily fitted a table top. After several improvements, SECAN approved the ETCRRM for use by NATO on 19 April 1954 [3].

Oberman
Several years earlier, in 1946, the Dr. Neher Laboratory of the Dutch Post Office (PTT) had started the development of a One-Time Tape machine at the request of the Dutch Government. Due to shortages in electronic components in the first years after WWII, it was built with approx. 100 electromechanical relays. The machine was named Colex, and was a development of Dr. Ir. Roelof Oberman, who would later become Professor at Delft University. A small number of these Colex machines were commissioned on 6 April 1949 for communication between the Dutch Foreign Office and its embassies in London (UK), Paris (France), Washington (USA) and Jakarta (Indonesia).

Colex was not a fast machine – it could only handle three characters per second – but its success resulted in the development of a successor: ECOLEX — which is short for Electronic COde-teLEX. Development was started in 1949, immediately after the introduction of the Colex, and the first prototypes were ready in early 1950, just 10 months after the release of the relay-based Colex.

Philips Usfa
As PTT was not interested in the commercial exploitation of the machine, the production was transferred to Philips Usfa, where it became known as Ecolex I. The machine was ready in mid-1953 and existed in two variants: 1 Ecolex Mark 1 and Mark 2. A description was sent to NATO on 4 August 1953 [4], but it was not until 12 August of the next year that the two machines were approved for COSMIC traffic and for NATO traffic higher than CONFIDENTIAL [5].

The price for a single Ecolex Mark 1 unit in 1955 was US$ 6000 and for an Ecolex Mark 2 unit 'just' US$ 3000, with a lead time of 12 and 11 months respectively [6]. The ETCRRM on the other hand was produced at a rate of 200 units per month and was available immediately at a unit price of just US$ 1200 [6]. ETCRRM therefore won the race. Ecolex I was in production until 1958, and a total of just 25 units were built before it was succeeded by the smaller transistorised Ecolex II.

  1. Mark 1 and Mark 2, also written as Mark I and Mark II, should not be confused with Ecolex I and Ecolex II which are two entirely different machines. Mark 1 and Mark 2 are two variants of the Ecolex I which was simply called 'Ecolex' back then.

Specifications
Designators
  • 3201
    PTT
    Prototype with valves
  • 3202
    PTT
    Prototype with transistors
  • US 8011/00
    Philips
    Production version: Ecolex II
  • US 8011/01
    Philips
    with 4-pin connectors
  • US 8011/02
    Philips
    Improved line impedance matching
  • US 8011/03
    Philips
    Improved alarm
  • US 8011/04
    Philips
    with 4-pin connectors
  • US 8011/05
    Philips
    Partly with printed wiring
  • US 8011/50
    Philips
    Modified for use with Creed tape reader 92
Nomenclature
  • 3201
  • Ecolex Mark II
  • Ecolex Mark II A
  • Ecolex I Mark 1


Literature
  1. Maarten Oberman, Staatsgeheim, De Beveiliging van Overheidsberichten
    State Secret, Government Communications Security (Dutch).
    2022. ISBN 978-9-4644-8870-8.
Documentation
  1. Ecolex I, User manual (French)
    Date unknown, but probably 1953. 1

  2. Ecolex Mark 1 and 2
    The Netherlands Government, 1 October 1954. SECRET. 1
  1. Document kindly provided by Maarten Oberman [7].

References
  1. Photographs from Philips Usfa
    Crypto Museum Archive. CM300624.

  2. Philips Usfa, Internal Memo L/5636/AvdP/JG
    23 August 1982, page 5. CM300428.

  3. NATO, Approval of Electronic Mixer ETCRRM
    SGM-311-54. 19 April 1954. NATO SECRET.
    Declassified by NATO on 17 November 1999 (IMSM-431-99).

  4. NATO, Netherlands On-Line Cipher Equipment
    SGM-1254-53. 17 August 1953. NATO SECRET.
    Declassified by NATO in 2006 (IMSM-0001-2006).

  5. NATO, Approval of Electronic Mixers ECOLEX Mk I and II
    SGM-556-54. 12 August 1954. NATO SECRET.
    Declassified by NATO in 2006 (IMSM-0001-2006).

  6. NATO, Automatic Crypto-Equipment Requirements for the Allied Command Atlantic
    SGM-560-55. 15 August 1955. NATO SECRET.
    Declassified by NATO on 24 November 1999 (IMSM-0431-99).

  7. Maarten Oberman, Personal correspondence
    June 2019. Crypto Museum, RMM Oberman archive.

  8. Maarten Oberman, Staatsgeheim, De Beveiliging van Overheidsberichten
    State Secret, Government Communications Security (Dutch).
    2022. ISBN 978-9-4644-8870-8.

  9. Survey of Versions of Ecolex I and Ecolex II equipments
    The Netherlands Government, 1 January 1959.
Further information
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Crypto Museum. Created: Saturday 18 February 2023. Last changed: Thursday, 23 February 2023 - 10:10 CET.
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