![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
I've bought RPG PDFs. They're never DRMed, but from DriveThruRPG they're allegedly watermarked.
I've bought DRM-free ebooks. Watermarking isn't mentioned, but I wonder if you could. I assume you could stow an extra blob in an EPUB file. What would you stow?
Encrypt that with a publisher secret key, stick it in the EPUB.
What does that get you? If someone is lazy and uploads their book to public places, you know where it came from. (You don't know for sure they did it -- maybe a hacker plundered their hard drive.) The encryption means someone can't forge an upload, pretending it came from someone else. The salt complicates known-plaintext attacks trying to recover the secret key.
Most ebooks have at least one image, the cover. You could use steganography to stash the blob there; it's encrypted text so should fit. Given that it's an encrypted blob, people may have trouble knowing whether you did anything at all, until you reveal your process.
After which, non-lazy pirates could delete the blob, or scramble where you're hiding the cover image. The watermark is hardly foolproof. But it's cheap.
I've bought DRM-free ebooks. Watermarking isn't mentioned, but I wonder if you could. I assume you could stow an extra blob in an EPUB file. What would you stow?
{
'customer': "Jane Doe",
'title': "This book is awesome",
'salt': "DEIFEFIGDBYDEADBEEF"
}
Encrypt that with a publisher secret key, stick it in the EPUB.
What does that get you? If someone is lazy and uploads their book to public places, you know where it came from. (You don't know for sure they did it -- maybe a hacker plundered their hard drive.) The encryption means someone can't forge an upload, pretending it came from someone else. The salt complicates known-plaintext attacks trying to recover the secret key.
Most ebooks have at least one image, the cover. You could use steganography to stash the blob there; it's encrypted text so should fit. Given that it's an encrypted blob, people may have trouble knowing whether you did anything at all, until you reveal your process.
After which, non-lazy pirates could delete the blob, or scramble where you're hiding the cover image. The watermark is hardly foolproof. But it's cheap.