Declassified NSA Document Reveals the Secret History of TEMPEST

"It was 1943, and an engineer with Bell Telephone was working on one of the U.S. government's most sensitive and important pieces of wartime machinery, a Bell Telephone model 131-B2. It was a top secret encrypted teletype terminal used by the Army and Navy to transmit wartime communications that could defy German and Japanese cryptanalysis."Then he noticed something odd."

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[Source: Disinfo.com