Mounting at boot time and unlocking with an ENCRYPTED key file

I have an encrypted root drive and a second encrypted drive with my data in my notebook. On booting I would like to enter the password only once for the root disk.
Here is a very good description: Mounting at boot time and unlocking with a key file
But I am not happy that this key file is not encrypted as well. If my computer is not locked theoretically it would be quite easy for a professional to find out my master password, if he finds the keyfile.
How can I make the keyfile encrypted? If this is not possible where can I store the password safely that it is already for mounting on boot?

Do not worry because the keyfile of the second encrypted partition is in the encrypted root partition.
That means the keyfile is already encrypted in the encrypted root drive.
You have to decrypt the root partition first and then find the keyfile in there.