Dracut now uses -c option for sha512hmac to verify the checksum, please implement it.
libkcapi-hasher does implement the '-c' option, however I just checked and on current F28 there is some issue with its command-line parsing... It turns out I made a mistake in this commit: https://github.com/smuellerDD/libkcapi/commit/3be3e18d4a2ed8be1cfcb7d05b175bc89b3d0e4f I have a fix ready, I'll push it shortly.
libkcapi-1.1.1-2.fc28 has been submitted as an update to Fedora 28. https://bodhi.fedoraproject.org/updates/FEDORA-2018-d744616145
libkcapi-1.1.1-3.fc28 has been submitted as an update to Fedora 28. https://bodhi.fedoraproject.org/updates/FEDORA-2018-d744616145
libkcapi-1.1.1-3.fc28 has been pushed to the Fedora 28 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2018-d744616145
libkcapi-1.1.1-3.fc28 has been pushed to the Fedora 28 stable repository. If problems still persist, please make note of it in this bug report.