How do you store a psuedo random number in flash.

Good Morning Everybody,

I'd like to store a random number in flash and later retrieve that number from flash after a reset.  We're planning on later implementing this with an app as a form of security.  I know how random number generation works but, am sketchy on the details of writing to and reading from flash without using UART.  I'm using PSOC4 BLE and PROC BLE.

Device A should receive a notification via Bluetooh from Device B;  Device B generates a random number and both store the number in flash to be read at a later time to do a comparison.

We can't use whitelisting because, the BLE address of a cellphone changes so often.

Thanks,

Michael