Sometimes it is useful to first define an abstraction. A good abstraction can reveal that some problems could be solved by the same solution. A good abstraction also makes it easier for us to communicate about the solution and understand its properties.
One such abstraction which I think should be defined and named is nonenumerable database. A database where you can query a value by a key, but you cannot enumerate all keys (nor all values). Even a database operator/administrator is not be able to do so.
At the same time, some problems are more intuitive than others and can help us better understand or even inform the abstraction. We will look at three examples where nonenumerable database can help: DNS/DNSSEC, gun ownership registry, and voting.