Autokey Cipher
The Autokey Cipher is a polyalphabetic substitution cipher. It is closely related to the Vigenère Cipher, but uses a different method of generating the key. It was invented by Blaise de Vigenère in 1586, and is in general more secure than the Vigenère Cipher.
Plaintext:
Ciphertext:

The following buttons can be used to manipulate the text into various forms such as uppercase, lowercase, reverse text, etc. The choice text chosen will be copied and a new page will be opened.

The Autokey cipher uses the following tableau (the 'tabula recta') to encipher the plaintext: