sdm-make-luks-usb-key

#!/bin/bash
#
# Create a LUKS encryption key and save it on a USB drive
#

function errexit() {
    echo -e "$1"
    exit 1
}

function errifrc() {
    [ $1 -ne 0 ] && errexit "$2 $1"
}
function ispdevp() {
    local dev="$1"
    [[ "$dev" =~ "mmcblk" ]] || [[ "$dev" =~ "nvme" ]] && return 0 || return 1
}

function getspname() {
    local dev="$1" pn="$2"
    ispdevp $dev && echo "${dev}p${pn}" || echo "${dev}$pn"
}

function pmsg() {
    echo "$1"
}

function printhelp() {
    echo $"
Usage: sudo sdm-make-luks-usb-key /dev/sdX [--switches]

Switches (all are optional)
* --hostname <hostname> -- If specified, the file hostname.txt is updated with hostname and LUKS key UUID
* --init or --initialize -- Format the USB device. If not specified, newly-created luks key will be added to USB
"
}

function parsecmd() {
    local cmd="$1" args="$2"
    local longopts="ext4,h,help,hidden,hostname:,init,initialize"

    OARGS=$(getopt -o h --longoptions $longopts -n 'sdm' -- $args)
    [ $? -ne 0 ] && errexit "? $cmd: Unable to parse command"
    eval set -- "$OARGS"
    while true
    do
	case "${1,,}" in
	    # 'shift 2' if switch has argument, else just 'shift'
	    --ext4) xext4=1                  ; shift 1 ;;
	    --hidden) xhidden=1              ; shift 1 ;;
	    --hostname) xhostname="$2"       ; shift 2 ;;
	    --init|--initialize) xinit=1     ; shift 1 ;;
	    --)                                shift ; break ;;
	    -h|--help) printhelp             ; shift ; exit ;;
	    *) errexit "? $0: Internal error" ;;
	esac
    done
    [[ $xhidden -eq 1 ]] && [[ $xinit -eq 0 ]] && errexit "? --hidden requires --init"
}

function checkusbkey() {
    #
    # Ensure that the USB disk has a FAT32 partition 1
    #
    local pn pstart pend psize pfs rest
    while read line
    do
	IFS=":" read pn pstart pend psize pfs rest <<< "$line"
	if [ "$pn" == "1" ]
	then
	    [[ "${pfs,,}" == "fat32" ]] || [[ "$pfs" == "EFI" ]] && return 0
	fi
    done < <(parted -ms $dev unit s print)
    return 1
}

#
# Main
#
dev=$1
xext4=0
xhidden=0
xhostname=""
xinit=0

parsecmd $0 "$*"

[ "$dev" == "" ] && errexit "Usage: sudo sdm-make-luks-usb-key /dev/sdX"
[ -b $dev ] || errexit "? $dev is not a block device"
sfdisk -l $dev >/dev/null 2>/dev/null || errexit "? No disk in $dev"

if [ $xinit -eq 1 ]
then
    #
    # Delete all partitions on $dev and create a single fat32
    #
    fatstart=2048s
    fatend=67584s
    extstart=67585s
    extend=198658s

    pmsg "> Initialize disk $dev for use as USB key disk"
    pmsg "> Wipe disk $dev"
    sgdisk --zap-all $dev >/dev/null 2>&1
    errifrc $? "? Error zapping all partitions on $dev"

    if [ $xhidden -eq 0 ]
    then
	pmsg "> Write DOS label on $dev"
	pmsg "label:dos" | sfdisk --force $dev >/dev/null 2>&1
	errifrc $? "? Error creating label on $dev"

	pmsg "> Create FAT32 partition on $dev"
	parted -s $dev mkpart primary fat32 ${fatstart} ${fatend}
	errifrc $? "? Error creating FAT32 partition on $dev"

	if [ $xext4 -eq 1 ]
	then
	    pmsg "> Create ext4 partition on $dev"
	    parted -s $dev mkpart primary ext4 $extstart $extend
	    errifrc $? "? Error creating ext4 partition on $dev"
	fi
    else
        pmsg "> Create GPT partitions on $dev"
        parted -s $dev mklabel gpt
        errifrc $? "? Error creating label on $dev"

	pmsg "> Create FAT32 partition on $dev"
        sgdisk --new 1:$fatstart:$fatend $dev >/dev/null
        errifrc $? "? Error creating FAT32 partition on $dev"
        sgdisk --typecode 1:ef00 $dev >/dev/null
        errifrc $? "? Error modifying partition 1 type on $dev"

	if [ $xext4 -eq 1 ]
	then
	    pmsg "> Create ext4 partition on $dev"
            sgdisk --new 2:$extstart:$extend $dev >/dev/null
            errifrc $? "? Error creating root partition on $dev"
            sgdisk --typecode 2:8300 $dev >/dev/null
            errifrc $? "? Error modifying partition 2 type on $dev"
	fi
    fi
    partprobe
    pmsg "> Format FAT32 file system on the first partition"
    mkfs.vfat -F 32 $(getspname $dev 1) >/dev/null 2>&1
    errifrc $? "? Error formatting FAT32 file system on $dev"
    if [ $xext4 -eq 1 ]
    then
	pmsg "> Format ext4 file system on the second partition"
	mkfs.ext4 -F $(getspname $dev 2) >/dev/null 2>&1
	errifrc $? "? Error formatting ext4 file system on $dev"
    fi
else
    checkusbkey $dev || errexit "? Device '$dev' not configured for USB disk; Consider using --init"
fi
lukskey=$(uuid -v4)
pmsg "> Create LUKS encryption key file /root/$lukskey.lek"
dd if=/dev/urandom bs=1 count=256 of=/root/$lukskey.lek >/dev/null 2>&1
#
# copy the .lek file to the USB disk
#
pmsg "> Copy LUKS key '$lukskey.lek' to the FAT32 partition"
mount -v $(getspname $dev 1) /mnt
cp /root/$lukskey.lek /mnt
if [ "$xhostname" != "" ]
then
    [ -f /mnt/hostkeys.txt ] || printf "%-24s %s\n" "Hostname" "LUKS Key UUID" >> /mnt/hostkeys.txt
    printf "%-24s %s\n" "$xhostname" "$lukskey" >> /mnt/hostkeys.txt
fi
umount -v /mnt
echo $"
> LUKS USB key disk is ready
  For sdm-cryptconfig use:  --keyfile /root/$lukskey.lek
  For cryptroot plugin use: keyfile=/root/$lukskey.lek
  For sdm-add-luks-key use: /usr/local/sdm/sdm-add-luks-key /path/to/$lukskey.lek

  You can delete '/root/$lukskey.lek' and access it from the USB key disk if desired

  NOTE: You need to have the key accessible when you customize or configure a disk using the key
        for an encrypted rootfs using sdm-cryptconfig, the cryptroot plugin, or sdm-add-luks-key
"
exit 0