Runs locally in your browser. Nothing you enter is uploaded to our servers.
Tips for Vigenère cipher
Classic Vigenère is educational, not modern cryptography.
Short or dictionary keys are easy to attack.
Repeating keystreams leak structure over long plaintext.
Use it to learn polyalphabetic ideas, then move to AES/libs.
Do not use Vigenère to protect real credentials.
Polyalphabetic demo, still not modern crypto
Processing stays in your browser — your input is not uploaded to our servers.
Vigenère repeats a keyword to shift letters. It beats Caesar against casual eyes and still falls to frequency analysis on long text.
Use it to learn repeating-key substitution. Do not ship it as product encryption.
Try Vigenère
Enter sample plaintext and a keyword
Short English sentences show the repeating key clearly.
Encrypt
Watch how the same letter maps to different ciphertext as the key index moves.
Decrypt with the same key
A wrong key yields junk — that is the teaching point, not a security guarantee.
Vigenère FAQ
Is Vigenère strong enough for passwords?
No. Use a password manager and modern hashing. This is a classroom cipher.
Why does a short key weaken it?
The key repeats. Long plaintext leaks the period, then each Caesar slice is easy.
Is processing local?
Yes. The demo never uploads the text.