Vigenère cipher
Encrypt and decrypt messages with the Vigenère cipher using a keyword. Keeps spaces, punctuation and capitals, and handles accented letters.
Type the message.
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Vigenère cipher: what it is for
Type the message and the keyword and choose encrypt or decrypt. Each letter is shifted by the matching letter of the key, which repeats along the text. Spaces, numbers, punctuation and capitals are kept, and accented letters are treated as the plain letter.
The text is never sent to a server: everything happens in your browser.
How to use
- Type the message.
- Enter the keyword.
- Choose encrypt or decrypt and copy.
When to use it
- Cryptography and history classes.
- Treasure hunts and puzzle games.
- Logic challenges and escape rooms.
Frequently asked questions
How does the Vigenère cipher work?
Each letter of the message is shifted in the alphabet by the value of the matching letter of the keyword, which repeats along the text. With the key LEMON, the first letter moves 11 positions (L), the second 4 (E), and so on. It is like several alternating Caesar ciphers.
Is it secure?
Not for real use. It was considered unbreakable for centuries, but since the 19th century it can be cracked with frequency analysis and the Kasiski test, especially with short keys. Today it is for study, games and logic puzzles.
What happens to accents and numbers?
Accented letters are encrypted as the plain letter, because the cipher uses the 26-letter alphabet. Numbers, spaces and punctuation stay the same and don't use up key letters.
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.