Encryption/Decryption

On encryption and decryption the yii framework uses the hashing method to do encrypt/decrypt.on these the yii framework use secret key to encrypt/decrypt without any access to the user.

What I want is I want to overwrite the data which the yii framework encrypt (or) encrypt using my own key and it only access by me not even the yii framework can’t.

On knowing the secret key only the person access the data to encrypt/decrypt.