Unlock LUKS using attached USB dongle at boot

luksunlockusb.sh

# /bin/luksunlockusb
#
# Add to /etc/initramfs-tools/modules
# usb-storage
#
# Add key:
# sudo cryptsetup luksAddKey /dev/sdb /home/user/.crypt_file
#
# Edit /etc/crypttab
# nvr_luks UUID=xxxxxxxxxxxx /home/user/.crypt_file luks
#
# sudo update-initramfs -u
#!/bin/sh
set -e
if [ ! -e /mnt ]; then
    mkdir -p /mnt
    sleep 3
fi
for usbpartition in /dev/disk/by-id/usb-*-part1; do
    usbdevice=$(readlink -f $usbpartition)
    if mount -t ext4 $usbdevice /mnt 2>/dev/null; then
        if [ -e /mnt/$CRYPTTAB_KEY.lek ]; then
            cat /mnt/$CRYPTTAB_KEY.lek
            umount $usbdevice
            exit
        fi
        umount $usbdevice
    fi
done
/lib/cryptsetup/askpass "Insert USB key and press ENTER: "