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Vigenère cipher

A Caesar shift that changes with every letter, set by a keyword. Three hundred years of codebreakers called it unbreakable.

Each letter of it is a shift: A is 0, B is 1, and on.

Result

The link opens a page that reads it. Without the key, your friend has to crack it. The message travels after the # in the link, which a browser never sends to our server.

Where it comes from

A Caesar shift that changes with every letter, set by a keyword. Giovan Battista Bellaso described it in 1553, but it took Blaise de Vigenère's name. For three hundred years it was called the cipher nobody could break, until Friedrich Kasiski published how in 1863.

A message worth knowing: Attack at dawn. The textbook example: the keyword LEMON turns ATTACK AT DAWN into LXFOPV EF RNHR.

Learn it by heart

This is the cipher desk from Covert Mail, our free app for learning codes. The app teaches Vigenère a few characters at a time, plans practice around the ones you miss, and keeps an archive of famous real messages to unlock. It is coming soon to the App Store and Google Play.

Coming soon to the App Store and Google Play

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