Vigenere Keyword Cipher Tool

Enter text and a keyword to encrypt or decrypt with the Vigenere cipher.

Key (letters only)

Encrypt Decrypt

Enter text on the left and click Apply Cipher to begin.

How to use

How is Vigenere stronger than the Caesar cipher?

Vigenere uses a repeating keyword to vary the shift for each letter, making simple frequency analysis ineffective.

Can Vigenere be cracked?

Yes. The Kasiski examination and index of coincidence methods can break Vigenere when the ciphertext is long enough.

Does the keyword need to be a real word?

No. Any sequence of letters works as the key. Longer, more random keys produce stronger encryption.

What happens to spaces and punctuation?

This tool passes non-letter characters through unchanged and only applies the cipher to alphabet letters.