Encrypt with keyword SECRET
text = ATTACK AT DAWNkey = SECRETmode = encrypt
Result: SFVFSC VY QLFV
Vigenère Cipher Demo
EDUCATIONAL DEMONSTRATION ONLY — The Vigenère cipher uses a keyword to apply different Caesar shifts to each letter, making it harder to break with simple frequency analysis. Named after Blaise de Vigenère, it was considered unbreakable for centuries ("le chiffre indéchiffrable").
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Enter your values and press Calculate — the result appears here.
Worked examples
Frequently asked questions
Is the Vigenère cipher secure?
No. It can be broken with Kasiski examination or frequency analysis. Modern ciphers like AES are vastly more secure.
How is it different from Caesar?
Caesar uses a single fixed shift. Vigenère uses a repeating keyword, applying a different shift to each letter.
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