A silly solution: Recreate a package every day, week or month and update package date to current time. A device will refuse to install an update that is older

A silly solution: Recreate a package every day, week or month and update package date to current time. A device will refuse to install an update that is older than factory specified interval. Of course the problem then is that your device now needs to have secure channel to NTP servers. Possibly they could use radio synchronization instead - same as used in radio controlled watches. It could be exploited, but it would be much harder to do remotely by network. It needs a bit of gymnastics, but it may still be easier on the long run than HTTPS. Your mileage can vary. Edit: Dear downvoter: Was I overly dumb or inaccurate with my proposition?