Vigenère Cipher Encoder & Decoder
Encode and decode the Vigenère cipher using a keyword — the classic polyalphabetic cipher that shifts each letter by a changing amount.
What is the Vigenère cipher?
The Vigenère cipher is a polyalphabetic substitution cipher that uses a keyword to vary the shift from letter to letter. For centuries it resisted codebreakers and earned the nickname "le chiffre indéchiffrable" — the indecipherable cipher.
How to use this Vigenère tool
- Choose Encode or Decode.
- Enter your keyword.
- Type your text and copy the result.
How the Vigenère cipher works
The keyword is repeated across the message, and each keyword letter sets the shift for the letter beneath it (A shifts by 0, B by 1, and so on). Because the shift keeps changing, the same plaintext letter can encode to different letters, which defeats the simple frequency analysis that breaks a single-shift cipher. Decoding applies the same keyword shifts in reverse.
Where it is used
The Vigenère cipher is a favourite in cryptography courses, puzzle hunts, and escape rooms because it is far stronger than a Caesar shift yet still simple to apply once you know the keyword.
More codes and ciphers
Explore the rest of the family: the Caesar Cipher, Atbash, Vigenère, and A1Z26. For other encodings, try the Morse Code Translator and the Binary Translator.
Free and private
This Vigenère cipher tool runs entirely in your browser — free, with no sign-up, and nothing you type is uploaded or stored.
Frequently asked questions
- What is the Vigenère cipher?
- The Vigenère cipher uses a keyword to apply a series of different Caesar shifts across the message. Each letter of the keyword sets the shift for the matching letter of the text, repeating the keyword as needed.
- How do I decode a Vigenère cipher?
- Enter the same keyword used to encode it and choose the Decode direction. The tool reverses each keyword-driven shift to recover the original message.
- Why is Vigenère stronger than Caesar?
- Because the shift changes from letter to letter based on the keyword, the same plaintext letter can map to different cipher letters. This defeats the simple letter-frequency analysis that breaks a Caesar cipher.
- Is it free and private?
- Yes — it runs entirely in your browser with no sign-up, and nothing you type is uploaded.
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