Free Online Tool
Vigenère Cipher
Use the polyalphabetic Vigenère cipher for advanced text encryption with keyword-based shifting.
How to Use Vigenère Cipher
- Type or paste your text into the input box.
- Enter a keyword (letters only) — it repeats across your text and sets the shift for each letter.
- Choose Encode or Decode; the result updates instantly.
- Use Copy to grab the output. Everything runs in your browser.
Each letter is shifted by the matching keyword letter (A=0 … Z=25); encoding adds the shift and decoding subtracts it, both mod 26. Case is preserved, and digits, spaces, and punctuation pass through without advancing the keyword.
Examples
Encode — input ATTACKATDAWN, keyword LEMON:
Output:
LXFOPVEFRNHR
Decode — input LXFOPVEFRNHR, keyword LEMON:
Output:
ATTACKATDAWN
Case preserved — input Hello World, keyword KEY:
Output:
Rijvs Uyvjn
Features
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All processing happens in your browser. No data is sent to servers.
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