Did You Know? How the Union Cracked the Civil War's Most Secure Cipher 🕵️‍♂️

Did you know that even though the Vigenère cipher was considered the strongest cipher during the American Civil War, the Union could regularly crack its messages?

This weakness was due to the Confederate States of America relying heavily on just three key phrases: Manchester Bluff, Complete Victory, and as the war neared its end, Come Retribution.

The cipher itself operates by encoding each letter of the plaintext with a Caesar cipher dependent on a corresponding letter of a key text.

However, the repetitive use of these key phrases made the Confederacy's encrypted messages vulnerable to being deciphered.

Interestingly, while the cipher is named after Blaise de Vigenère, it was actually invented by Giovan Battista Bellaso.

The cipher gained a false reputation of being unbreakable until Friedrich Kasiski published a method to decrypt it in eighteen sixty-three.

Had the Confederates used more varied or complex keys, their communication might have remained secret and could have had a different impact on the war's outcome.