Free Vigenère Cipher Tool
The Vigenère Cipher tool encrypts or decrypts text using a keyword. Each letter is shifted by a different amount based on the keyword, making it stronger than a simple Caesar cipher.
Vigenère is a polyalphabetic cipher — a step up from the single-shift Caesar Cipher and ROT13. None of them are secure today; for real protection use AES.
How to use the Vigenère Cipher
- 1 Enter the text you want to encrypt or decrypt.
- 2 Enter the keyword — it is repeated across the message to give each letter a different shift.
- 3 Choose encrypt or decrypt.
- 4 Copy the result, and keep the keyword to reverse it later.
How to Use
Enter your text and a keyword, then choose Encrypt or Decrypt. Only letters are transformed; case is preserved and non-letters stay untouched.
- Keyword-based polyalphabetic cipher
- Encrypt and decrypt modes
- Preserves case and non-letters
Frequently asked questions
How does the Vigenère cipher work?
It applies a Caesar shift that changes per letter, driven by a repeating keyword. Letter one might shift by 3, letter two by 15, and so on. Because the shift varies, the same plaintext letter encrypts differently at different positions, which defeats simple frequency analysis.
Why was it considered unbreakable?
For roughly three centuries it resisted attack and was known as le chiffre indéchiffrable. Its weakness is the repeating key: once you guess the key length, the message splits into several ordinary Caesar ciphers, each of which falls to frequency analysis.
Should I use it to protect anything real?
No. It is a historical and educational cipher with no place in modern security — a determined attacker with enough ciphertext can recover the key. Use AES for anything that actually needs protecting, and treat this as a puzzle or a teaching tool.
Related Security & Cryptography Tools
You might also need
Tools from other categories that people pair with the Vigenère Cipher: