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On-line/off-line OTT mixing cipher machine
In 1959, Philips started development of the Ecolex-IV as the successor
of the Ecolex-I
and Ecolex-II models.
Like the previous models, it is based on
the Vernam cipher,
whereby data from a teletype (or punched paper tape)
is mixed with a random cipher tape.
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If the cipher tape consists of truely random numbers,
the cipher is unbreakable.
Sometimes however, a pseudo-random number generator
was used to create the cipher tapes, making it less secure.
The image on the right shows part of an Ecolex-IV.
The top half of the image shows the controls. Below that are
the two punch tape readers.
The one closest to the control panel is for the cipher tape,
whilst the other one is used for the clear-text tape.
More and better photographs will be
presented here as and when they become available.
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This is the rear panel of the Exolex-IV.
Please note the white telex connector at the center of the image,
mounted on a sub-assembly. This allowed the machine to be delivered
with a variety of connectors, such as the Siemens Telex connector
shown here.
In most cases, the machines had two 6 mm jacks for
connection to a telex-line or a radio modem.
The Ecolex-IV can be used on both 2-wire and 4-wire
telex networks.
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The machine is very heavy and is mounted on 4 springs, probably to
guarantee smooth operation in a vehicle. The interior of the machine
is filled with so-called 'functional blocks'; small encapsulated
electronic circuits, that can be regarded as the predecessors of
Integrated Circuits (ICs).
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This image shows a close-up of the two paper tape readers.
The rear one was used for the cipher tape. It has a small integrated
knife at the left, that destroys the cipher tape immediately after use.
This was done to prevent the tape from being used again.
The front tape reader was used for the clear-text tape. At the right
it has a special bracket with an ingegrated switch. The clear-text
tape had to be fed through this bracket, so that the machine would
stop once the source tape had finished.
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The Ecolex-IV was developed between 1959 and 1963 and approximately
750 units were built. In the late 1960s, about 150 units were modified
with the so-called Tarolex pseudo-random key
generator.
The machine remained in service until the mid-1970s when they were
gradually replaced by the Ecolex-X.
The Ecolex-IV was a very reliable machine with a very low failure rate.
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The operating principle of the Ecolex-IV is identical to other cipher
machines in the mixer class. At present, it is unclear whether the
Ecolex was able to exchange messages with other mixer brands, such
as the Siemens M-190.
The Ecolex-IV service documentation suggests that it is compatible
with mixer machines used by other NATO countries,
but to date we have not been able to verify this.
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Like most cipher machines of the mixer-class, the Ecolex-IV is not
(and never was) classified. It is the combination of the machine and
a NATO-issued cipher tape, that was classified as NATO SECRET.
Because of the fact that one-time tapes (OTT) were used with the Ecolex-IV,
it is impossible to use the machine to break old intercepts, as all
original OTP-tapes were destroyed per protocol immediately after use.
Not many Ecolex-IV machines have survived and some can be seen at
the Royal Dutch Signals Museum.
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