Offline/Online cipher machine
- Wanted item
Excolex-X was an online cipher machine for synchronous data connections,
developed between 1965 and 1972 by Philips Usfa in Eindhoven (Netherlands) for the Royal Dutch Army. It was the successor to the
OTT machine and was based in part on the earlier
The machine is also known as Ecolex-10,
UA 8040 and
Rather than using One-Time Tapes (OTT)
like its predecessor the Ecolex-IV,
the Ecolex-X uses a built-in key stream generator.
This was done to overcome the typical key-tape distribution problems
of the old mixer class machines.
The image on the right shows a typical Ecolex-X unit as it was on public
display at the Royal Dutch Signals Museum in 2009 .
It is housed inside a ruggedized heavy metal case, with the crypto-settings
hidden behind an enforced TEMPEST door.
36 Thumbwheels are used for the daily key,
The key stream generator inside the Ecolex-X was based (in part) on the earlier
TROL project. TROL was developed for a NATO evaluation,
but was never taken into production as the evaluation was lost to the
British ALVIS (BID 610).
Development of the Ecolex-X took from 1965 to 1972 and faced many hurdles.
The intial design was based on ELCOMA standard hybrids (mini circuits),
but the machine was redesigned later with flat-pack ICs, after which the
complete construction was changed 
(see also below).
Development was delayed a number of times, due to a delayed order, ambiguous
specifications and TEMPEST problems.
Finally, after a series of additional
developments and modifications, the machine was rolled out.
In total 388 machines were built, of which the majority went to the Dutch Army.
A few machines were delivered to the Dutch Ministry of Foreign Affairs .
The above Ecolex-X machine has serial number 005 and belongs to the very
first prototype series delivered to the Dutch Army for testing.
The initial machines were based on ELCOMA standard hybrid circuits,
but at some point the unit was completely redesigned with flat-pack ICs
that had just become available.
At the same time, the complete construction of the machine was changed
The new model was called UA-8040/02.
The image on the right shows the UA-8040/02 version of the Ecolex-X.
It has serial number 333 and shows a number of differences.
The lock of the heavy TEMPEST door has been mechanically improved.
The key is now used to unlock a spring-loaded lever that in turn is used
to open the door.
The layout of the controls behind the door has also been changed.
The test and control switches are no longer located to the left of the
thumbwheel switches, but below them.
The images below were taken in 2011 in the Military Communications Museum
of Mathieu Driessen (ON8PO) in Belgium. The Ecolex-X is part of a
complete HF/VHF radio shelter
on the back of a DAF truck . The Ecolex is mounted in the top left corner
of the shelter.
Whilst development of the Ecolex-X took a rather long time, it was decided
that a separate key stream generator would be developed as a gap-fill
solution. In 1966/67, the so-called Tarolex 19" was developed
for use with a modified Ecolex-IV machine. Like
the Ecolex-X, Tarolex was also based on the earlier
TROL developments. Approx. 150 Tarolex units were
delivered to the Dutch Army and an equal number of existing
Ecolex-IV machines was modified for them
Ecolex-X was suitable for off-line and on-line use, via telephone lines as
well as over radio. When used on-line, the internal key generator would
generate a continuous key stream, even when the operator was not typing any
text. This way, it was impossible for an interceptor to determine the start
and end (and hence the length) of a message. When used off-line, a separate
(Siemens-based) tape reader would be used to feed data into the Ecolex-X.
The image on the right shows a small signals van, that was used for many
years by the Royal Dutch Army. Inside the van is a desk with a standard
Siemens T-100 teletype machine at the center. To the right of the teletype
is a Philips RT-3600 radio set.
To the left of the teletype is the Siemens tape reader that was used to
feed data to the Ecolex-X.
The Ecolex-X itself is hidden under the desk at the left.
A suitable line-interface is mounted in the top left.
The image was taken at the Royal Dutch Signals Museum in 2009 .
As Ecolex-X was used by the Dutch Army and was also approved for use by NATO,
it had to comply with the most stringent military specifications.
This included testing the device under severe 'wet' conditions.
The image on the right shows a production Ecolex-X machine under soak test.
The picture was taken at the production facility in Eindhoven in the
early 1970s .
A further close-up of the wet Ecolex-X below.
Following the success of the Ecolex-X, Philips developed its successor - the
Ecolex 20 - in the mid-1980s. Although the Ecolex 20 design was completed
and was even listed in Jane's Military Communications of 1986, it was never
taken into full production.
It did not meet the requirements of the era and development of the all-new
ZODIAC integrated communication
system was well underway.
➤ More information
- Ecolex X KL/TGA-3572, Lesstencil: 23-10A
Training instructions (Dutch). Verbindingsdienst, August 1985.
- Royal Dutch Army, Ecolex-X list of items (Dutch)
Detaillijst vercijfer- ontcijferuitrusting KL/TGA-3572.
- Royal Dutch Army, Instruction sheet (Dutch)
Instructiekaart voor de bediening van een telegrafie-eindstation,
bestaande uit TT-4230/TT-4231, KL/TGA-3572 en TH-3676(A).
IK11-519/3. 27 September 1976.
- Royal Dutch Army, Ecolex-X User Manual (Dutch)
Technische handleiding vercijfer- ontcijferuitrusting KL-TGA-3572.
Bediening. 1e en 2e echelons onderhoud.
26 January 1973.
- Royal Dutch Army, Ecolex-X Maintenance Manual (Dutch)
Vercijfer- en ontcijferuitrusting KL/TGA-3572.
3e echelons technische beschrijving en onderhoud.
3TH11-959. 12 September 1973.
- Royal Dutch Army, Ecolex-X Wiring Diagrams (Dutch)
Vercijfer- en ontcijferuitrusting KL/TGA-3572.
4e en 5e echelons onderhoud. Bedradings- en montagegegevens.
4/5TH11-959/2. 5 October 1976.
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© Crypto Museum. Created: Sunday 16 June 2013. Last changed: Sunday, 25 June 2017 - 14:47 CET.