https://www.braingle.com/brainteasers/codes/autokey.php
https://www.boxentriq.com/code-breaking/cipher-identifier
The Vigenère Autokey Cipher is a more secure variant of the ordinary Vigenère cipher. It encrypt the first letters in the same way as an ordinary Vigenère cipher, but after all letters in the key have been used it doesn't repeat the sequence. Instead it begins using letters from the plaintext as key.
https://www.braingle.com/brainteasers/codes/autokey.php
https://www.boxentriq.com/code-breaking/cipher-identifier
The Vigenère Autokey Cipher is a more secure variant of the ordinary Vigenère cipher. It encrypt the first letters in the same way as an ordinary Vigenère cipher, but after all letters in the key have been used it doesn't repeat the sequence. Instead it begins using letters from the plaintext as key.