If you want data to be 100% secure, never store it!
I was once in a meeting with some rather big-wigs from the DoD and the discussion went on and on and on about how this data could be secured.
My cohort and i (invited to provide some technical perspective) had more than enough of this nonsense and he got the floor and offered "It could always be stored in a write-only file - one that no process or code could read". Unfortunately, the 2-star thought this was a fantastic idea (no IT guy this one). This was received with many grins and a few chuckles - until the 2-star realized he'd bit . . . Meeting ended not long after . . .
And no one died . . .