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KW-7 →
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TTY cipher machine - not in collection

AFSAM-9, later TSEC-KW-9, was an on-line non-reciprocal rotor-based cipher machine for 5-level teleprinter signals (TTY, Telex), developed around 1952 by the US National Security Agency (NSA). It was developed in parallel with the KL-7 and used the same 36-point cipher rotors.

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.

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).

The KW-9 was used with one of the following operating procedures:

    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.
Contact problems
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.

  1. Jerry Proc and contributors, KW-9
    Retrieved 15 April 2024.

  2. Ed Fitzgerald, A History of US Communications Security Post WWII
    NSA, undated. Obtained via the Government Attic. pp. 81-83, 93.

  3. National Cryptologic Museum, Photograph of KW-9 ciphermachines
    NCM/NSA. Retrieved 16 April 2024.
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Crypto Museum. Created: Monday 15 April 2024. Last changed: Tuesday, 16 April 2024 - 10:44 CET.
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