@h_kabiri "Atmel has nowhere explained..."
It's Atmel's (or, rather, Microchip's) product - so there's no use asking in an ST forum for such proprietary information.
You need to contact Microchip support:
https://microchipsupport.force.com/s/
https://community.atmel.com/forums/general-security-discussions
A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.