Free Online Tool
Autokey Cipher
Self-synchronizing stream cipher that uses the message itself as part of the key.
How to Use Autokey Cipher
- Enter plaintext and a letters-only keyword.
- Choose Encrypt; the default keyword is QUEENLY and spaces do not consume key characters.
- For decryption, switch modes and supply the same keyword used to encrypt.
- Keep Preserve Spaces on for matching punctuation and spacing, then copy the result.
The component starts with the keyword, then extends the keystream with plaintext letters. Each alphabetic character is shifted by its corresponding keystream letter.
Examples
Keyword QUEENLY — plaintext:
ATTACK AT DAWN
Output:
QNXEPV YT WTWP
Keyword KEY — plaintext:
HELLO
Output:
RIJSS
Features
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