My case is that I want to make the data protected even from people who have access to the back-end (the keys store), so they couldn't read it without the user's (represented by the client app, in my case the browser) assistance.
One option is to have the decryption keys stored on the client and passed with each request which sounds pretty messy to me and i'm not sure I want my keys to wander around the net like this. What I imagine though is that the client will keep some token (it might be a password the user knows) and the decryption can't happen without it.
I thought about using the purpose string for this, I have the feeling it is not a good idea since its main purpose is isolation. On the other hand it is part of the additional authenticated data used for subkey derivation. (based on this article https://learn.microsoft.com/en-us/aspnet/core/security/data-protection/implementation/subkeyderivation?view=aspnetcore-2.1#additional-authenticated-data-and-subkey-derivation).
I came across some examples that create their own symmetric encryption with a lower level classes. (like this post Encrypt and decrypt a string in C#?). Since I'm not an expert in this area I would like to use as much build in classes as possible.
What is the recommended way to achieve what I need with the classes from the Data Protection API? (I'm using .net core 1.1 on Ubuntu)
