Lewis Carroll invented a code he was certain nobody could ever break
In 1868, Lewis Carroll published 'The Alphabet Cipher', a method for encoding messages that he described as 'absolutely undecipherable' — unreadable even if an enemy captured the exact method used to make it, as long as they didn't have the secret keyword. Was he right that it couldn't be cracked?
Reveal the answer
He wasn't right, and the cipher wasn't even new: it used the same keyword-and-grid system as the three-centuries-older Vigenère cipher, which French cryptanalyst Kasiski had already shown how to break in 1863 — five years before Carroll's 'uncrackable' version was published. Repeating keywords leave statistical patterns that reveal the key length, no matter how clever the alphabet.
— Lewis Carroll, Vigenère cipher — 'The Alphabet-Cipher', 1868