This is great work, but I’m not clear on why this qualifies as DRM at all. It sounds like the OP reverse engineered a protocol for rendering pages from a book to the web client. Sure, rotating the glyph ids every API call is annoying but it hardly qualifies as encryption or even obfuscation, just an extra mapping step the decoder needs to handle.

Sure seems like whoever at Amazon wrote this didn’t realize that it backdoors their DRM.