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Vigenère Cipher

Encrypt or decrypt text with the Vigenère cipher, which uses a repeating keyword to shift letters.

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How to use the Vigenère

Choose Encrypt or Decrypt.
Enter a keyword (letters only) — a longer key is stronger.
Type your message; the result updates live.
Click Copy to use the result.

Privacy: this tool runs entirely in your browser. Your input is never sent to, received by, or stored on any server — there are no uploads and no tracking of what you enter.

About Vigenère

What is the Vigenère cipher

It extends the Caesar cipher by using a keyword: each letter is shifted by the corresponding letter of the repeating key, making it much harder to break by frequency analysis.

How to use it

Enter a keyword (letters only), choose encrypt or decrypt, and type your message.

History

Once called 'le chiffre indéchiffrable' (the unbreakable cipher), it resisted casual cryptanalysis for centuries.

Frequently asked questions

Is the Vigenère cipher secure?

Not by modern standards, but far stronger than Caesar; it was historically significant.

What makes a good key?

A longer, random keyword is stronger than a short or repetitive one.

Does case matter?

Letters are shifted regardless of case; non-letters pass through.