[U-Boot] password for u-boot

Hi everyone, I have a technical question about u-boot. Is there any way to set up a security (for instance password...) either any users cannot handle u-boot environments variables ? When the user plug his serial sâble, I do not want to allow him to see any the contents variable envrionments. I found something about CONFIG_ENV_AES but it is no clear about what the user can/cannot do. http://events.linuxfoundation.org/sites/events/files/slides/elce-2014.pdf Thank you :)