Crypto Goes to War: The American Civil War 1861–1865

The nineteenth century marked the beginning of the use of technology in many areas, and cryptology was no exception. The invention of the telegraphTelegraph and its rapid and easy communication ushered in the twilight of traditional forms of cryptography. It also marked the beginning of a century and a half of rapid development of new techniques in both cryptography and cryptanalysis, all starting during the American Civil WarAmerican Civil War. This chapter looks at the cipher systems used by both the Union and Confederate sides during the American Civil WarAmerican Civil War. It also presents a description of the biggest cryptanalytic breakthrough of the nineteenth century, the breaking of the unbreakable cipher, the Vigenère.