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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 used throughout WWII and was so reliable that it was used
well into the 1950s, when it was replaced by 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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According to a recently released NSA document, SIGABA was such a reliable
machine that is was used throughout the 1950s. Some of its operating principles
were not declassified until the year 2000 [1].
Shortly afterwards, US patent 6,175,625
was released [2].
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The design of the SIGABA machine was filed for a patent on 15 December 1944,
close towards the end of WWII. The patent was not published however, until
16 January 2001, shortly after the machine was declassified.
The patent lists Laurence F. Stafford and Donald W. Seiler as the inventors.
The patent covers 14 pages, including the 5 drawing sheets, and registers
21 claims. The drawing on the left is taken from the first page of the
patent. It shows the machine after the removing the metal cover.
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SIGABA had three bank of 5 wheels each, the contacts of which
are visible in the drawing above. The main bank (at the rear)
contained 5 wheels with 26 contacts each. These were the main
cipher wheels and worked similar to
the Enigma machine.
The second bank (middle) also contained 5 wheels with 26 contacts
each, but these were used to control the movement of the main
cipher rotors. These were called the control wheels.
The third bank (front) contained 5 wheels that were smaller
than the others. They only had 10 contacts each and would not
move during encipherment. Together with the control wheels,
controlled the movement of the cipher wheels.
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Combined Cipher Macine (CCM)
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SIGABA was developed in the late 1930s and was used by the US Army
throughout WWII for communication at the highest level.
Towards the end of WWII, there was an increasing need for secure communication
with the British Armed Forces. As a result, SIGABA was made interoperable
with a modified British Typex machine.
A modified SIGABA could then exchange messages with a modified Typex.
The common machine was known as the Combined Cipher Machine (CCM),
and was used from November 1943 onwards.
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It was used for secure Allied communication during WWII and even
served with the newly established NATO for a few years after the war.
The wheel assembly was removed and replaced by an assembly of just
5 coding wheels. Less secure than the original, but interoperable
with a modified British Typex.
The machine shown here is one of the very few CCM versions of
SIGABA that have survived. Unfortunately, the wheel assembly and the
motor are missing from this one.
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Furthermore, the motor-assembly has been removed, so we assume that
this machine has been used as a donor for spare parts in order to
repair other machines.
If you have any parts for this machine or if you have additional
information, please contact us.
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© Copyright 2009-2011, Paul Reuvers & Marc Simons. Last changed: Mon,02 Jan 2012.22:07:32
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