Yes, sub-resources can be encrypted and spec-wise stylesheets are just resources (files in the manifest that aren't in the spine, like images, fonts, video files, etc.). That said EPUB does not fully define any standard encryption/DRM mechanism so any DRM scheme is,at this point, proprietary.
Yes, sub-resources can be encrypted and spec-wise stylesheets are just resources (files in the manifest that aren't in the spine, like images, fonts, video files, etc.). That said EPUB does not fully define any standard encryption/DRM mechanism so any DRM scheme is,at this point, proprietary.