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Electric cipher machine (ECM)
SIGABA was a US cipher machine based on the
electromechanical rotor principle. It was developed in
the late 1930s as a joint effort of the US Army and Navy
[1]. At the time it was considered a
superior cryptomachine, intended to keep high-level
communications absolutely secure. It was so reliable
that it was used throughout the 1950s, when it was
replaced by newer machines like the
KL-7. As far as we know, SIGABA was never broken.
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The image on the right shows one of the few SIGABA
machines that have survived. It has the appearance of a
rather bulky typewriter, featuring a full keyboard at
the front. SIGABA is motor-driven and can print its text
on a small strip of paper that runs across the front.
The machine has three banks of 5 wheels each, which is
clearly visible in the patent below.
The main bank (at the rear) contained 5 wheels with 26
contacts each. These were the main cipher wheels
and worked similar to the German
Enigma machine (more below). |
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Before, during and after WWII, the US Army and Navy each
developed their own cryptographic systems. Neither
service shared their knowledge with the other one,
except for limited cooperation in the field of enemy
signals intelligence. The first exception to this 'rule'
was the development of SIGABA. It combined the knowledge
of top cryptographers William F. Friedman and Frank B.
Rowlett (Army) and Lieutenant Commander Laurence Safford
(Navy).
The machine was called SIGABA by the US Army and
ECM (Electric Cipher Machine) by the Navy. It is
also known as Converter M-134 and CSP-888/889
(Navy). A modified Navy version is known as the
CSP-2900.
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