Masked Dispatches: Cryptograms and Cryptology in American History, 1775-1900

Chapter 4. America's First Espionage Code

There was developed during the Renaissance era the first code sheet with code and word elements listed in a single alphabetical-numerical order. In the seventeenth century, Antoine Rossignol vastly improved the basic design when he introduced a two-part system and scattered the elements so that they were not in alphabetical-numerical sequence. Instead, he prepared two lists: one with words in alphabetical order for encoding and the other in numerical sequence for decoding. In eighteenth- century Europe, codes of 1,500 to 3,000 numbered words were used to conceal especially sensitive data in diplomatic dispatches.

For example, Hugh Elliot, England's ambassador and espionage officer in Berlin during the American ...