EpubSplit does set the identifier in content.opf. Since it's meant to be unique and all.
Example:
Code:
<?xml version="1.0" ?>
<package version="2.0" xmlns="http://www.idpf.org/2007/opf" unique-identifier="epubsplit-id">
<metadata xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:opf="http://www.idpf.org/2007/opf">
<dc:identifier id="epubsplit-id">epubsplit-uid-1707591258</dc:identifier>
But that could be (optionally?) copied from the source.
theducks, I'm still confused. You seem to be saying that you
don't know how to make the split book work with encrypted fonts?
If you can't tell me exactly what needs to be copied/changed, and you can't share a source epub (or a scrambled version) so I can try to figure it out, I'm not going to be able to help you.