Wednesday, April 01, 2009

Washington-Moscow Hot Line

The ETCRRM mixer
The direct link between United States and the Soviet Union, and later the Russian Federation, is a well known legacy of the Cold War. The Cuban missile crisis, generally regarded as the moment in which the Cold War came closest to nuclear war, made the US and USSR realise that reliable and secure communications are essential in event of a crisis.

The Hotline became operational in August 1963 and was a full duplex teleprinter (Telex) circuit. Although the hot line always has been shown as a red telephone in movies and popular culture, the option of a speech link was turned down as it was believed that spontaneous verbal communications could lead to miscommunications, misperceptions, incorrect translation or unwise remarks, which are serious diplomatic disadvantages in times of severe crisis. Nevertheless, the red phone myth lived a long life.

The real hot line was a direct cable link, routed from Washington-London-Copenhagen-Stockholm-Helsinki to Moscow. It was a double link with commercial teleprinters, one link with English character teleprinters and the other link with Cyrillic character teleprinters. The links were encrypted with one-time tapes by means of four ETCRRM's (Electronic Teleprinter Cryptographic Regenerative Repeater Mixer). The one-time tape encryption provided unbreakable encryption, absolute security and privacy. Although a higly secure system, the unclassified standard teleprinters and ETCRRM's (see image, by Jerry Proc) were sold by commercial firms and therefore did not disclose any secret crypto technology to the Soviets.

In 1974 the hot line underwent a first modernization and a new link was established by two American Intelsat and two Soviet Molniya II satellites. The original wire circuit was kept as a back-up. A second upgrade, the addition of a high-speed facsimile link, became operational in 1986. From that moment on, the Hot Line consists of two satellite links and one wire teleprinter circuit.

A very detailed description of the Washington-Moscow hot line is found on Jerry Proc's great Crypto Machines, which also contains a ETCRRM page. The hot-line is also described in detail on Top Level Communications and on Crypto Museum. On my Focus on Machines you can see the ETCRRM and other machines. The ETCRRM was a pretty popular device, used for high level military communications in several countries.

For more information one one-time tapes, please visit my one-time pad page. If you're curious about 'Red Phones' and what they actually are, you can check out Jerry's Red Phone webpage.

1 comment:

atle said...

A little comment on your artickle about the hotline. The machine you wrote about in your artickle (ETCRRM) was in fact developted and invented by a norwegian, Bjørn Rørholt, a former WWW2 radiooperator with the SOE. As a norwegian I'm proud of the invention and the role it played in the cold war.
If someone wants more information, you can get it from me by mailing me at
You can also read about it in norwegian atÅrsmeldinger/NSM årsmelding 2008.pdf