Encoding & Number Bases
Vigenère Cipher
Encrypt and decrypt text with the Vigenère polyalphabetic cipher using a keyword.
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What is Vigenère?
The Vigenère cipher uses a keyword to vary the shift per position, defeating simple frequency analysis. It was considered unbreakable for centuries (le chiffre indéchiffrable) until the Kasiski attack of 1863.
How it works
Letters of the keyword (A=0 … Z=25) shift the plaintext letters one by one, repeating the keyword as needed; non-letters pass through without consuming a key letter.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
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