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← UK Rotor
Electromechanical cipher machine
- wanted item
Portex was a British
electromechanical cipher machine that was used by
secret services in the UK during the 1940's and 1950's.
The machine is similar to the
German Enigma machine,
but is more advanced in that it features 8
cipher wheels with 26 contacts each, and has
irregular stepping.
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Plaintext is entered one character at a time by setting the alphabet ring
at the left side to the desired letter and rotating the crank at the right.
The letter then fires an electric current into the drum, starting with
the leftmost wheel. The current that leaves the wheels at the right is
used to drive the printer which is mounted at the left. The output
is delivered on a (pre-gummed) strip that leaves the machine
at the left rear.
Apart from similarities with the German Enigma,
Portex also seems to have 'borrowed' features of the Swedish/Swiss
Hagelin pin-wheel machines.
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The design of the printer, the alphabet ring and the character
counter (all mounted to the left of the cipher wheels) show great resemblance
to portable Hagelin machines such as the
M-209
and C-446.
In fact, Portex
can best be seen as a hybrid between a
Hagelin M-209
and and Enigma G.
Portex was used by British secret services but also by the Canadian Army.
The civil version was generally black, whilst the military variant was
typically green and had some additional features, such as a push-button
above/behind each cipher wheel. It is known that the military variant was
still 1in use with the Canadian Army in the early 1960's [1].
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The image below shows a Portex cipher machine seen from the front left
with its top lid open. At the front right are the eight electric cipher
wheels that are moved mechanically on each key press. At the front left
is the printer mechanism, the text entry knob (alphabet ring) and the counter.
Towards the rear, mounted behind the cipher wheels, are a couple of solenoids
which are used to operate the machine's wheel stepping mechanism. The exact
operation of the mechanism is currenly unknown. Any additional information
about this machine, its operation and its use would be
much appreciated.
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Portex shows great resemblance to the
Enigma machine that was used
by the German Army throughout WWII. Whilst the
Enigma I featured
regular stepping, similar to the operation of an odometer,
there was one class of Enigma machine that was driven by a stepping gear
and had multiple turnovers on each wheel. This variant was known
as the Zählwerksmachine
or Enigma G.
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The image on the right shows a close-up of the 8 cipher wheels inside
a Portex machine as it was on public display at the
Enigma Reunion in 2009,
where it was presented by David White.
Machines with irregular stepping are generally more difficult to predict
and hence are more difficult to break. The stepping of the British Portex
machine is nearly identical to that of the
Zählwerk Enigma and it is most
likely that part of the design was 'borrowed' from it.
➤ More about Zählwerk Enigma
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We are currently looking for additional information about the Portex and
ideally, a real machine for our collection. The exact operation of the
machine is currently unknown and we do not know exactly how
input and output were handled.
If you have more information, please contact us.
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© Crypto Museum. Created: Sunday 25 January 2015. Last changed: Sunday, 25 February 2018 - 14:10 CET.
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