This is a request to enhance grub with not trivial crypto features. All the code is readily available in 5 patch files located in http://grub.johnlane.ie This request is create an ebuild with a toggleable USE flag to support those features as I think gentoo should have those features. Upstream doesn't seem to have them.
related bug on arch: https://bugs.archlinux.org/task/42851
Sorry, I'm not patching in features. Submit this request upstream if you want to see it.