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Vigenère cipher

Encrypt and decrypt text with the classic Vigenère keyword cipher.

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Vigenère cipher
Type a keyword, paste your text and the Vigenère cipher shifts every letter by the corresponding letter of the key — A shifts by 0, B by 1, and so on, with the key repeating for as long as the message runs. Switch the direction to decrypt and the same key turns the ciphertext back into the original. Everything updates live as you type, so you can watch a plaintext scramble letter by letter.
The tool is built for the places the Vigenère cipher actually lives today: geocaching mystery caches, escape room puzzles, CTF challenges, scavenger hunts and classroom lessons on classical cryptography. Teachers use it to demonstrate why a polyalphabetic cipher defeats simple frequency counting, and puzzle solvers use the decrypt direction to test candidate keys against an inscription in seconds.
The key uses letters only — digits and symbols typed into it are ignored, and a key with no letters at all is reported rather than guessed around. The cipher operates on the plain A–Z alphabet: accented letters, digits, punctuation and emoji are never shifted. With "Keep non-letters" on they pass through in place without advancing the key; turn it off for classic solid ciphertext with everything else stripped. "Preserve case" keeps your capitalization, or produces traditional all-caps output when disabled.
One honest note: the Vigenère cipher was called "le chiffre indéchiffrable" in the 16th century, but it has been breakable since 1863 and is a puzzle today, not protection. For anything genuinely confidential, use the encrypt text tool with real AES encryption. Either way your text never leaves the browser — nothing you type here is uploaded anywhere.
FAQ
How does the Vigenère cipher work?
Each letter of the key names a shift: A means shift by 0, B by 1, up to Z by 25. The first letter of your text is shifted by the first key letter, the second by the second, and the key repeats when it runs out. Decryption applies the same shifts in reverse, which is why the exact same key must be used for both directions.
Is the Vigenère cipher secure?
No. It resisted attack for three centuries, but Kasiski published a general break in 1863 and modern tools crack short keys in milliseconds. Treat it as a puzzle and a piece of history. For anything that actually needs protecting, use the encrypt text tool, which applies real AES-256 encryption.
What happens to accented letters, digits and punctuation?
The cipher shifts only the 26 unaccented Latin letters. Accented letters such as é or ü, digits, punctuation and emoji pass through unchanged and never consume a key letter — so "attack at dawn" and "attackatdawn" encrypt their letters identically. Turn off "Keep non-letters" to drop everything that is not a letter instead.
Why is my key rejected?
The key needs at least one letter A–Z, because only letters define a shift. Digits and symbols in the key are skipped, so a key like "k3y!" is treated as "KY". A key made entirely of digits or symbols has no letters left and produces an error instead of a silent guess.
Is my text uploaded anywhere?
No. The cipher runs entirely in your browser and neither your text nor your key ever leaves your device.