In 1917, AT&T engineer Gilbert Vernam invents a cipher machine to encrypt transatlantic telegraph messsages sent by the War Department to United States troop commanders in Europe during WWI. The system, which is modified by the Army Signal Corps, is later proved to be unbreakable. The so-called One Time Pad Cipher is the first example of online encryption.
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AT&T archive videos and imagery courtesy of the AT&T Archives and History Center.