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Grub2 allows to encrypt the boot device with LUKS. Booting the system, it shows a prompt for entering the passphrase. In my case, the passphrase should be secure, so it is very long.
Is it possible - analogous to the kernel cryptsetup - to load a LUKS key from a usb device?
(It's a duplicate of https://stackoverflow.com/questions/29186720/grub2encrypt-boot-load-keyfile-from-usb-device , but as mentioned, it was as the wrong place.)