Re: Script for loop-AES key generation

[Max Vozeler <max@xxxxxxxxxxxx>]

Hi Jari,

On Tue, Nov 14, 2006 at 09:58:43AM +0200, Jari Ruusu wrote:
> There have been few cases where v3 key file and v2 losetup/mount were
> used to set up a file system, and after upgrade to v3 losetup/mount,
> mounting the file system failed. There is a warning about this problem
> in loop-AES README file, but not everyone reads README files.
>
> May I suggest adding a check that losetup is recent enough. Something
> like this:

>     strings /sbin/losetup | grep -q -s multi-key-v3
>     if [ $? != 0 ] ; then
>         echo "too old losetup version"
>     fi

Indeed, that's a useful check. Given that strings(1) is part
of binutils, which may not be installed on all systems, I made it
run only if strings can be found. Thanks for your suggestion.

cheers,
Max

Index: debian/loop-aes-keygen
===================================================================
--- debian/loop-aes-keygen	(Revision 1325)
+++ debian/loop-aes-keygen	(Revision 1326)
@@ -137,6 +137,11 @@
 	return 0
 }
 
+check_multikey_support ()
+{
+	strings /sbin/losetup | grep -q -s multi-key-v$1
+}
+
 keygen()
 {
 	version=$1
@@ -174,6 +179,12 @@
 	exit 1
 fi
 
+if [ "$version" -gt 1 ] && [ -x /usr/bin/strings ]; then
+	if ! check_multikey_support $version; then
+		echo "Warning: /sbin/losetup too old for v$version keys."
+	fi
+fi
+
 if [ -e $keyfile ]; then
 	echo "Keyfile $keyfile exists. Aborting."
 	exit 1

#!/bin/sh
#
# loop-aes-keygen - Create loop-AES encryption keys
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 2 dated June, 1991.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program;  if not, write to the Free Software
# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA.
# 
# Copyright 2005-2006, Max Vozeler <xam@xxxxxxxxxx>
#
# $Id: loop-aes-keygen 1326 2006-11-18 14:03:56Z xam $
#

set -e

umask 077

cipher=
userids=
rnd=/dev/random
version=3

usage()
{
	cat << USAGE
usage: loop-aes-keygen [opts] <keyfile>

  -v <1|2|3>	   Key format (Default: $version)
  -u userid        Encrypt for GnuPG pubkey <userid>
  -c cipher        Use GnuPG cipher <cipher>

USAGE
}

get_options()
{
	while getopts 'v:s:c:u:h' f
	do
		case $f in
		v) 
			version=$OPTARG
			;;

		c)
			cipher=$OPTARG
			;;

		s)
			rnd=$OPTARG
			;;

		u)
			userids="$userids $OPTARG"
			;;
			
		h)
			usage
			exit 0
			;;
		esac
	done
	shift `expr $OPTIND - 1`

	keyfile=$1
	
	if [ -z $keyfile ]; then
		echo No output file. Aborting
		usage
		exit 1
	fi

	if [ $version -lt 1 ] || [ $version -gt 3 ]; then
		echo Unsupported key format: $version
		exit 1
	fi
}

check_safe_loop()
{
	loopdev=$1

	opts=$(/sbin/losetup $loopdev 2>&1)
	if [ $? -ne 0 ]; then
		echo "Error: Check for $loopdev failed ($opts)"
		exit 1
	fi
		
	# If loop entry has an encryption= option assume it's safe
	if echo "$opts" | grep -q encryption=; then
		return 0
	fi

	return 1
}

check_safe_swap()
{
	if [ ! -r /proc/swaps ]; then
		echo Error: Cannot read /proc/swaps
		exit 1
	fi

	unsafe=
	while read line
	do
		set -- $line
		case $1 in
		/dev/loop*)
			if ! check_safe_loop $1; then
				unsafe=$1
				break
			fi
			;;
		Filename*)
			;;
		*)
			unsafe=$1
			break
			;;
		esac
	done < /proc/swaps

	if [ $unsafe ]; then
		echo Fatal: Unsafe swap detected: $unsafe
		exit 1
	fi

	return 0
}

check_multikey_support ()
{
	strings /sbin/losetup | grep -q -s multi-key-v$1
}

keygen()
{
	version=$1
	keyfile=$2
	gpgargs=$3

	# These are the known loop-AES key formats:
	#  v1.x    1     45 bytes           AES key         
	#  v2.x   64   2880 bytes(45 * 64)  AES keys       
	#  v3.x   65   2925 bytes(45 * 65)  #65 is md5 seed
	case $version in
	1) nkeys=1 ;;
	2) nkeys=64 ;;
	3) nkeys=65 ;;
	*) return 1 ;;
	esac

	bytes=$((45*$nkeys))
	head -c $bytes $rnd | uuencode -m - | head -n $(($nkeys+1)) | tail -n $nkeys | gpg $gpgargs > $keyfile
}

get_options $*

if ! check_safe_swap; then
	exit 1
fi

if ! [ -x /usr/bin/gpg ]; then
	echo "Error: gpg not found"
	exit 1
fi

if ! [ -x /usr/bin/uuencode ]; then
	echo "Error: uuencode not found - see package sharutils"
	exit 1
fi

if [ "$version" -gt 1 ] && [ -x /usr/bin/strings ]; then
	if ! check_multikey_support $version; then
		echo "Warning: /sbin/losetup too old for v$version keys."
	fi
fi

if [ -e $keyfile ]; then
	echo "Keyfile $keyfile exists. Aborting."
	exit 1
fi

gpgargs="--armor"

if [ "$userids" ]; then
	gpgargs="$gpgargs --encrypt"
	for id in $userids; do
		gpgargs="$gpgargs --recipient $id"
	done
else
	gpgargs="$gpgargs --symmetric"
fi

if [ $cipher ]; then
	gpgargs="$gpgargs --cipher-algo=$cipher"
fi

if ! keygen $version $keyfile "$gpgargs"; then
	echo An error occured while creating the key file.
	exit 1
fi

exit 0