How do I use the Vigenère Cipher?

Provide a key=WORD parameter Same key encrypts and decrypts with op=dec Non-letter characters are preserved (punctuation, numbers, spaces)

Is the Vigenère Cipher free and private?

Yes — it runs in your browser, requires no signup for basic use, and your data never leaves your device. The Vigenère cipher was considered unbreakable for 300 years — it earned the nickname 'le chiffre indéchiffrable' in 19th-century France.

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Vigenère Cipher

Polyalphabetic cipher using a keyword — stronger than Caesar

1 credit

Line 1: key=WORD op=enc|dec — then body

Ciphertext

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