Definitely not for "after civilization ends"
> vital component after civilization ends?
I don't know why you assume it's simple and low tech. Even today nobody would know how to use it, except a handful of history fans and multiclass engineer-cryptographers.
Yes, it doesn't use modern integrated circuits, but compared to (for instance) a smartphone with a crypto app, it's a fiendishly complex device requiring trained operators.
Biting the hand that feeds IT
