Theoretically, you could add a signatures.xml file to the epub. However, I don't know of any epub app that actually supports this feature.
I.e., you'd also have to provide readers with a standalone app that validates the checksums.
It'd probably be easier to generate an MD5 checksum for the whole epub.
A download checker for Humble Bundle book bundles.
Since there seems to be no answer from this community regarding an application meeting the request in my question, I decided to make one myself.
When you buy a bundle from Humble Bundle, whether books or games, they send you a web link to a HTML page (which I call here the download page).. You can then ...