Ecolex I Mk 2 →
Two versions of the Ecolex I existed: one that operated on the 26 letters of
the Latin alphabet and was compatible with existing mechanical OTT
machines, and one that operated on all 32 characters of the
ITA2 telegraph alphabet.
These two versions were known as Mark 1 and Mark 2 respectively.
The image on the right shows the Ecolex Mark 1 with its front cover
removed. As far as we know, it is the only surviving specimen of this model.
It is currently held in an internal collection of the Dutch
Department of Defense.
The Ecolex Mark 2, is a completely different machine that
allows all characters of the ITA2 alaphabet
to be encrypted, including carriage return, linefeed, etc.,
as it works on all 32 ITA2 characters.
It is smaller and contains fewer switching elements than the Ecolex Mark 1.
The Excolex I Mark 1 — at the time simply known 1 as the Ecolex Mark I —
was intended to be fully backwards compatible with the mechanical OTT
machines of the era — in particular the
Hagelin C-446/RT —
and also with the manual One-Time Pad (OTP) methods of the era.
This way, embassies that did not (yet) have an Ecolex, could still
encrypt/decrypt messages (either mechanically or manually) as before,
with the key provided on paper rather than on tape .
As a result of this, only the 26 characters of the Latin alphabet could
be used, whilst the stunt characters (linefeed, carriage return, etc.) are
passed straight through, so that cryptograms should still be printed in
spaced 5-letter groups. One exception is the SPACE character, which is
replaced by the letter 'X'. 2
Because of these limitations and exceptions, the Ecolex I Mark 1 is an
extremely complex device, which is built around 68 switching elements, each
built around an E90CC double-tetrode valve.
The Excolex Mark 2 is simpler as it lacks these limitations [B].
The exact production quantity of the Ecolex I is currently
unknown, but from Philips Usfa archives it is known that
approx. 25 machines were built by Philips between 1953 and
1956 . If we include the prototypes and early production machines made
by PTT, it is likely that the total production quantity of the Ecolex I
is somewhere between 30 and 40 units. In 1955, the machine was succeeded by
the Ecolex II, which is actually the transistorised version of the
Ecolex Mark 2.
➤ More about the Ecolex Mark 2
➤ More about the Ecolex II
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.
In some languages, such as Dutch, the space was replaced by the 'X'.
Different letters were used other languages, such as K (French, Italian,
Spanish) or Z (English).
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
The process is also known as mixing, which is why
are also known as mixers.
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.
In the Ecolex I Mark 1, the process is slightly more complicated,
as only the 26 letters of the Latin alphabet are encrypted. Other
characters, such as carriage return (CR) and linefeed (LF),
appear unchanged in the output stream. Furthermore, the SPACE character
is replaced by another letter.
➤ More about the Vernam Cipher
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
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).
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.
➤ More information
Double tape reader
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
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
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
and easily fitted a table top. After several improvements, SECAN
approved the ETCRRM
for use by NATO on 19 April 1954 .
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
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).
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.
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 , 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 .
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 .
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 .
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.
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.
PTTRelease version, 25 chars + space
Philips26 letters, or 25 letters + space
Philipswith 4-pin connectors
Estimated production quantity of Ecolex I Mark 1 and Mark 2 together.
Document kindly provided by Maarten Oberman .
- Photographs from Philips Usfa
Crypto Museum Archive. CM300624.
- Philips Usfa, Internal Memo L/5636/AvdP/JG
23 August 1982, page 5. CM300428.
- NATO, Approval of Electronic Mixer ETCRRM
SGM-311-54. 19 April 1954.
Declassified by NATO on 17 November 1999 (IMSM-431-99).
- NATO, Netherlands On-Line Cipher Equipment
SGM-1254-53. 17 August 1953.
Declassified by NATO in 2006 (IMSM-0001-2006).
- NATO, Approval of Electronic Mixers ECOLEX Mk I and II
SGM-556-54. 12 August 1954.
Declassified by NATO in 2006 (IMSM-0001-2006).
- NATO, Automatic Crypto-Equipment Requirements for the Allied Command Atlantic
SGM-560-55. 15 August 1955.
Declassified by NATO on 24 November 1999 (IMSM-0431-99).
- Maarten Oberman, Personal correspondence
June 2019. Crypto Museum, RMM Oberman archive.
- Maarten Oberman, Staatsgeheim, De Beveiliging van Overheidsberichten
State Secret, Government Communications Security (Dutch).
2022. ISBN 978-9-4644-8870-8.
- Survey of Versions of Ecolex I and Ecolex II equipments
The Netherlands Government, 1 January 1959.
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© Crypto Museum. Created: Thursday 13 June 2013. Last changed: Sunday, 19 February 2023 - 13:41 CET.