Data at rest.

This has been a hot topic for many years, now. Nobody knows how to make it inherently secure.

If you encrypt it, somebody knows the key. If you hide the key, somebody knows where it is.

It is also called Information Security and there is research on preventing unauthorized access to websites

- Cloud Security

- IoT Security

- Blockchain Security

to name a few.

IoT security combined with AI

I think you may find that this answers your question (and solves the problem)

Article Securely Encrypting Data At Rest