Encrypt or decrypt text with the Vigenere cipher, a classical polyalphabetic substitution that shifts each letter by a repeating keyword.
Supported Tools:
Letters only are used; case and non-letters in the text are preserved.
Encrypt and decrypt text with the Vigenere cipher using a keyword. Runs entirely in your browser.
The Vigenere cipher is a classical polyalphabetic substitution cipher from the 16th century. Instead of one fixed shift like Caesar, it shifts each letter by a different amount taken from a repeating keyword, which long made it resistant to simple frequency analysis and earned it the nickname le chiffre indechiffrable. This tool encrypts or decrypts a message with a keyword you choose. It is meant for learning, puzzles and CTF challenges, not for protecting real secrets.
Input:
Text: ATTACKATDAWN Keyword: LEMON
Output:
LXFOPVEFRNHR
Is the Vigenere cipher secure?
No. It can be broken with the Kasiski examination or index of coincidence once the key length is found. Treat it as educational, not as real encryption.
What characters can the keyword contain?
Only letters are used. Any digits or symbols in the keyword are ignored, and the remaining letters set the shifts.
Are spaces and punctuation kept?
Yes. Non-letters are copied to the output unchanged and do not advance the keyword, and the case of each letter is preserved.
Does my text leave the browser?
No. Everything is processed locally in your browser.