It means they can't steal the key, so the attacker has to actually have root on the device whenever new data is sent. That's risky for the attacker as they coul

It means they can't steal the key, so the attacker has to actually have root on the device whenever new data is sent. That's risky for the attacker as they could be found out and possibly have their entry vector / zero day patched worldwide. It also has open source random number generators, another defence against a passive attacker and requiring them to have root on the device.