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KW-7 Encryption Machine - A Cold War electronic data encryption machine developed by the US National Security Agency (NSA) and built by Honeywell.


The KW-7 was used to transmit low-level classified tactical teletype traffic. Officially known as TSEC/KW-7. Used by the US military, other US government agencies and several European governments.

The KW-7 was housed in a substantial metal enclosure, with all connections at the rear and all controls on the front. A daily cryptographic key was inserted by a wired plugboard through a lockable front panel. Later models provided for plug-bock and card-reader daily key insertion.

The KW-7 was usually connected to a Teletype Model 28 teletype and/or a tape reader communicating over a normal teletype circuit. The crypto key was usually changed on a daily basis. The KW-7 did not provide traffic flow security because it only transmitted data when a message was being sent.

In US and Canadian radar sites the KW-7 was usually housed in the operations building in a secured room. The crypto operator was armed with a sidearm. Elaborate destruction instructions detailed how to destroy the KW-7, the manuals and the keys.


USS Pueblo (AGER-2) Captured by North Korea with Crypto Assets Aboard.

During the Cold War the KW-7 was compromised several times that were known. The most famous cases included the Walker spy ring and the capture of the USS Pueblo on 23 Jan 1968 with two KW-7s on board. The Pueblo capture was not considered catastrophic at the time because, even though the North Koreans were able to get one of the machines working, it was thought that they had no access to the daily crypto keys and those keys were immediately changed. The discovery of the John A. Walker spy ring changed all that because Walker was able to pass the crypto keys and equipment modification orders to his Soviet handlers from 1967 until he was exposed in 1985.

It is believed that the North Koreans and the Soviets cooperated with the result that the soviets were able to build KW-7 replicas and decode US naval KW-7 traffic well into the 1980s. This enabled the Soviets to know where US submarines were at all times during this period and may have also compromised US Air Force B-52 strikes during the Vietnam War

KW-7 Encryption Machine

KW-7 Encryption Machine
Element Value Notes
Nomenclature KW-7
Developed By National Security Agency (NSA)
Manufacturer Honeywell
Type Crypto Machine
Estimated Number Built 38,000
Estimated Cost $4,500
Introduced Early 1960s
Last used About 1992
KW-7 Crypto Machine (Card-Reader Version) at the National Cryptologic Museum, Fort Meade, Maryland.

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