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Rotor USA NSA KW-7 → ← KL-7
The rotors were placed in a so-called rotor basket — similar to
the rotor basket of the KL-7 —
but instead of 8 rotors, it held 9 rotors, one of which (rotor 5) was
stationary. The current positions of the other 8 moving rotors were visible
through 8 small windows in the rotor basket.
The KW-9 was aimed to process around 100 five-letter groups per minute,
which is more than 8 characters per second. But at this speed, the
electromechanics of the machine are pushed to their limits,
as a result of which the KW-9 became notorious for losing synchronisation.
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With a life span of less than 10 years, the machine was short-lived [2].
During this time it was used only sparingly. It was sufficiently secure,
but its electromechanical problems significantly affected its reliability [2].
The machine was taken out of service around 1966 [1], well before the
contemporary manually operated KL-7 was decommissioned.
The image above shows the KW-9 that is held in the collection
of the National Cryptologic Museum (NCM)
at Fort Meade (USA).
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The KW-9 was used with one of the following operating procedures:
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- ATHENA
With this procedure, the message key was sent in-clear.
This was the least secure operating procedure, comparable to the
POLLUX procedure of the KL-7.
- IRIS
With thisprocedure, the message key was send in encrypted form.
it was more secure than the ATHENA procedure and is comparable tp
the ADONIS procedure of the KL-7.
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Like the contemporary KL-7 — which used the same 36-point
cipher rotors — the KW-9 had reliability issues that were mainly
related to the beryllium-copper (BeCu) rotor contacts. BeCu is
known to easily oxidise and become non-conducting.
Most contact problems could be avoided however with proper maintenance.
Cleaning the contacts
with alcohol does not help, but rubbing them with the tools supplied
in the maintenance kit does.
But as the speed of the KW-9 was significantly higher than that of the
KL-7, the reliability issues were much bigger. In practice this
often led to loss of synchronisation. This is probably also the reason
that it was is service for less than 10 years, which is very
unusual for military equipment.
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© Crypto Museum. Created: Monday 15 April 2024. Last changed: Tuesday, 16 April 2024 - 10:44 CET.
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