What is the purpose of your modified idea? We already have DRM systems. What will a new implementation of a DRM system do to help anyone? To make yet another incompatible-with-everyone-else store? Or maybe to make vendors have to spend a lot of money to upgrade their device firmware for no good reason? (Hint: Not happening...)
What difference does it make if files are encrypted with a per-user key vs. a per-device key? Either publishers want DRM or they don't, and if they don't then they don/'t need
this DRM at all, or they do want DRM, in which case the implementation will still have to hide the book from the user.
It sounds like you are attempting to propose a scheme for delivering files to users, which only the user can access. Rather than letting everyone download it but encrypting it for the user, why not just do what everyone has been doing for, like, a really long time, and use website logins?
