commit 84d438569603eb8448a3965bbe1fb7b54168a1fc
parent b9b7927e819556aae3881b98903b5fc5ccd8858c
Author: Jaromil <jaromil@dyne.org>
Date: Fri, 22 Mar 2013 21:13:59 +0100
new creation system in 3 steps and some tips in documentation
Diffstat:
2 files changed, 241 insertions(+), 26 deletions(-)
diff --git a/doc/Tomb_User_Manual.org b/doc/Tomb_User_Manual.org
@@ -0,0 +1,25 @@
+
+
+when creating a tomb make sure the device mapper is loaded among kernel modules
+or creation will fail and leave you in the dust.
+
+modprobe dm_mod
+modprobe dm_crypt
+
+to create a tomb on a server (even VPS) is possible, but the problem becomes the little
+available entropy. in order to fix this one can use EGD the Entropy Gathering Daemon.
+
+on Debian, do:
+
+sudo aptitude install libdigest-sha1-perl
+sudo aptitude install ekeyd-egd-linux
+
+/etc/default/ekeyd-egd-linux
+
+wget http://egd.sourceforge.net/
+
+perl ./egd.pl
+
+/etc/init.d/ekeyd-egd-linux start
+
+
diff --git a/src/tomb b/src/tomb
@@ -640,10 +640,12 @@ exec_safe_post_hooks() {
create_tomb() {
_message "Commanded to create tomb $1"
- # running as root, remembering the uid:gid
+ # we run as root, but remember the original uid:gid to drop
+ # privileges when not needed anymore
if option_is_set -U; then _uid="`option_value -U`"; fi
if option_is_set -G; then _gid="`option_value -G`"; fi
+ # if swap is on, we remind the user about possible data leaks to disk
if ! option_is_set -f && ! option_is_set --ignore-swap; then check_swap; fi
if ! [ $1 ]; then
@@ -651,10 +653,11 @@ create_tomb() {
return 1
fi
- if ! [ $2 ]; then
- create_cipher=aes-cbc-essiv
+ # the encryption cipher for a tomb can be set at creation using -o
+ if ! option_is_set -o; then
+ create_cipher="`option_value -o`"
else
- create_cipher=${2}
+ create_cipher=aes-cbc-essiv:sha256
fi
tombfile=`basename $1`
@@ -662,7 +665,10 @@ create_tomb() {
# make sure the file has a .tomb extension
tombname=${tombfile%%\.*}
tombfile=${tombname}.tomb
- tombsize=$opts[-s]
+
+
+ # require the specification of the size of the tomb (-s) in MB
+ tombsize="`option_value -s`"
[ $tombsize ] || die "Size argument missing, use --size"
@@ -674,20 +680,26 @@ create_tomb() {
return 1
fi
+ # check if the key is set manually then use the one existing
if option_is_set -k; then
- tombkey="`option_value -k`.tomb.key"
- else
- tombkey="${tombdir}/${tombfile}.key"
- fi
+ tombkey="`option_value -k`"
+ if [ -e "${tombkey}" ]; then
+ _message "Use an existing key to lock the new tomb:"
+ ls -lh ${tombkey}
+ fi
- if [ -e "${tombkey}" ]; then
- _warning "tomb key already exists. Quitting."
- ls -lh ${tombkey}
- return 1
+ # this does a check on the file header, virtuosism by hellekin
+ # [[ `file =(awk '/^-+BEGIN/,0' $1) -bi` =~ application/pgp ]]
+ if ! is_valid_key ${tombkey}; then
+ _warning "The key seems invalid, the application/pgp header is missing"
+ die "Operation aborted."
+ fi
+ else
+ tombkey="new" # generate it new later
fi
-
+
_success "Creating a new tomb in ${tombdir}/${tombfile}"
-
+
if [ -z $tombsize ]; then
_message "No size specified, summoning the Tomb Undertaker to guide us in the creation."
"$TOMBOPENEXEC" &
@@ -751,14 +763,18 @@ create_tomb() {
fi
_success "Setup your secret key file ${tombkey}"
- touch ${tombkey}
- chown ${_uid}:${_gid} ${tombkey}
- chmod 0600 ${tombkey}
- gen_key ${keytmp}/tomb.tmp > ${tombkey}
+ if [ "$tombkey" = "new" ]; then
+ tombkey="${tombdir}/${tombfile}.key"
+ touch ${tombkey}
+ chown ${_uid}:${_gid} ${tombkey}
+ chmod 0600 ${tombkey}
+ gen_key ${keytmp}/tomb.tmp > ${tombkey}
+ fi
if ! is_valid_key ${tombkey}; then
_warning "The key does not seem to be valid"
fi
+
# if [ $? != 0 ]; then
# _warning "setting password failed: gnupg returns 2"
# umount ${keytmp}
@@ -772,7 +788,7 @@ create_tomb() {
# for security, performance and compatibility
# XXX: More for compatibility then, because xts-plain is better nowadays.
cryptsetup --batch-mode \
- --cipher ${create_cipher}:sha256 --key-size 256 \
+ --cipher ${create_cipher} --key-size 256 \
luksFormat ${nstloop} ${keytmp}/tomb.tmp
if ! [ $? = 0 ]; then
@@ -807,6 +823,162 @@ create_tomb() {
_success "Your tomb is ready in ${tombdir}/${tombfile} and secured with key ${tombkey}"
}
+# This is a new way to create tombs which dissects the whole create_tomb() into 3 clear steps:
+# - dig a .tomb (the large file) using /dev/random (takes some minutes at least)
+# - forge a .key (the small file) using /dev/urandom (good entropy needed)
+# - lock the .tomb file with the key, binding the key to the tomb (requires dm_crypt format)
+
+forge_key() {
+ _message "Commanded to forge key $1"
+
+ # we run as root, but remember the original uid:gid
+ # to set the permissions as readable for the calling user
+ if option_is_set -U; then _uid="`option_value -U`"; fi
+ if option_is_set -G; then _gid="`option_value -G`"; fi
+
+ if ! [ $1 ]; then
+ _warning "no key name specified for creation"
+ return 1
+ fi
+
+ # if swap is on, we remind the user about possible data leaks to disk
+ if ! option_is_set -f && ! option_is_set --ignore-swap; then check_swap; fi
+
+ # the encryption cipher for a tomb can be set at creation using -o
+ if ! option_is_set -o; then
+ create_cipher="`option_value -o`"
+ else
+ create_cipher=aes-cbc-essiv:sha256
+ fi
+
+
+ # create the keyfile in tmpfs so that we leave less traces in RAM
+ keytmp=`safe_dir tomb`
+ (( $? )) && die "error creating temp dir"
+ xxx "safe_dir at $keytmp"
+
+ mount tmpfs "${keytmp}" -t tmpfs -o size=1m
+ if [ $? != 0 ]; then
+ _warning "cannot mount tmpfs filesystem in volatile memory"
+ rm -r "${keytmp}"
+ die "operation aborted."
+ fi
+
+ tombkey="$1"
+
+ _message "this operation takes time, keep using this computer on other tasks,"
+ _message "once done you will be asked to choose a password for your tomb."
+ _message "To make it faster you can move the mouse around."
+ _message "If you are on a server, you can use an Entropy Generation Daemon."
+
+ touch ${keytmp}/tomb.tmp
+ chmod 0600 ${keytmp}/tomb.tmp
+ random_source=/dev/random
+ if option_is_set --use-urandom; then
+ random_source=/dev/urandom
+ fi
+
+ if [[ $DD = "dcfldd" ]]; then
+ $DD bs=1 count=256 if=$random_source of=${keytmp}/tomb.tmp statusinterval=1
+ else
+ $DD bs=1 count=256 if=$random_source of=${keytmp}/tomb.tmp
+ fi
+ if ! [ -r ${keytmp}/tomb.tmp ]; then
+ _warning "cannot generate encryption key"
+ umount ${keytmp}
+ rm -r $keytmp
+ die "operation aborted."
+ fi
+
+ _success "Choose the password of your key: ${tombkey}"
+ _message "(you can also change it later using 'tomb passwd')"
+ touch ${tombkey}
+ chown ${_uid}:${_gid} ${tombkey}
+ chmod 0600 ${tombkey}
+
+ tombname="$tombkey"
+ # the gen_key() function takes care of the new key's encryption
+ gen_key ${keytmp}/tomb.tmp > ${tombkey}
+
+ # this does a check on the file header, virtuosism by hellekin
+ # [[ `file =(awk '/^-+BEGIN/,0' $1) -bi` =~ application/pgp ]]
+ if ! is_valid_key ${tombkey}; then
+ _warning "The key does not seem to be valid"
+ _warning "Dumping contents to screen:"
+ cat ${tombkey}
+ _warning "--"
+ umount ${keytmp}
+ rm -r $keytmp
+ die "operation aborted."
+ fi
+
+ ${=WIPE} ${keytmp}/tomb.tmp # no need really, but anyway
+ umount ${keytmp}
+ rm -r ${keytmp}
+
+ chown ${_uid}:${_gid} ${tombkey}
+
+ _message "done forging $tombkey"
+ _success "Your key is ready:"
+ ls -lh ${tombkey}
+}
+
+# dig a tomb
+dig_tomb() {
+ _message "Commanded to dig tomb $1"
+
+ # if swap is on, we remind the user about possible data leaks to disk
+ if ! option_is_set -f && ! option_is_set --ignore-swap; then check_swap; fi
+
+ if ! [ $1 ]; then
+ _warning "no tomb name specified for creation"
+ return 1
+ fi
+
+
+ tombfile=`basename $1`
+ tombdir=`dirname $1`
+ # make sure the file has a .tomb extension
+ tombname=${tombfile%%\.*}
+ tombfile=${tombname}.tomb
+
+
+ # require the specification of the size of the tomb (-s) in MB
+ tombsize="`option_value -s`"
+
+ [ $tombsize ] || die "Size argument missing, use --size"
+
+ [[ $tombsize != <-> ]] && die "Size argument is not an integer"
+
+ if [ -e ${tombdir}/${tombfile} ]; then
+ _warning "A tomb exists already. I'm not digging here:"
+ _warning " `ls -lh ${tombdir}/${tombfile}`"
+ return 1
+ fi
+
+ _success "Creating a new tomb in ${tombdir}/${tombfile}"
+
+
+ tombsize_4k=`expr $tombsize \* 1024 / 4`
+ _message "Generating ${tombfile} of ${tombsize}Mb (${tombsize_4k} blocks of 4Kb)"
+ # we will first touch the file and set permissions: this way, even if interrupted, permissions are right
+ touch ${tombdir}/${tombfile}
+ chmod 0600 "${tombdir}/${tombfile}"
+ $DD if=/dev/urandom bs=4k count=${tombsize_4k} of=${tombdir}/${tombfile}
+
+ if [ $? = 0 -a -e ${tombdir}/${tombfile} ]; then
+ _message " `ls -lh ${tombdir}/${tombfile}`"
+ else
+ die "Error creating the tomb ${tombdir}/${tombfile}, operation aborted."
+ fi
+
+ _success "Done digging $tombname"
+ _message "your tomb is not yet ready, you need to forge a key and lock it:"
+ _message "tomb forge ${tombname}.tomb.key"
+ _message "tomb lock ${tombname}.tomb ${tombname}.tomb.key"
+}
+
+
#internal use
#$1 is the keyfile we are checking
is_valid_key() {
@@ -844,9 +1016,9 @@ get_lukskey() {
return $ret
}
-#internal use
-#$1 the lukskey to encrypt
-#it respects --kdf and --tomb-pwd
+# internal use
+# $1 the lukskey to encrypt
+# honored options: --kdf --tomb-pwd
gen_key() {
local lukskey=$1
# here user is prompted for key password
@@ -879,7 +1051,8 @@ gen_key() {
fi
-
+ # KDF is a new key strenghtening technique against brute forcing
+ # see: https://github.com/dyne/Tomb/issues/82
_verbose "KDF method chosen is: '`option_value --kdf`'"
kdf_method=$(cut -d: -f1 <<<`option_value --kdf` )
case $kdf_method in
@@ -887,7 +1060,7 @@ gen_key() {
if [[ -z $KDF_PBKDF2 ]]; then
die "The tomb use kdf method 'pbkdf2', which is unsupported on your system"
fi
-#one parameter: iter time in seconds
+ # --kdf takes one parameter: iter time (on present machine) in seconds
seconds=$(cut -d: -f2 -s <<<`option_value --kdf`)
if [[ -z $seconds ]]; then
seconds=1
@@ -897,7 +1070,9 @@ gen_key() {
_verbose "Microseconds: $microseconds"
pbkdf2_salt=`${KDF_PBKDF2}-gensalt`
pbkdf2_iter=`${KDF_PBKDF2}-getiter $microseconds`
- tombpass=`${KDF_PBKDF2} $pbkdf2_salt $pbkdf2_iter 64 <<<"${tombpass}"` #64bytes=512bits is the key length (huge!)
+ # We use a length of 64bytes = 512bits (more than needed!?)
+ tombpass=`${KDF_PBKDF2} $pbkdf2_salt $pbkdf2_iter 64 <<<"${tombpass}"`
+
header="_KDF_pbkdf2sha1_${pbkdf2_salt}_${pbkdf2_iter}_64\n"
;;
""|null)
@@ -1758,7 +1933,12 @@ main() {
subcommands_opts[__default]=""
subcommands_opts[open]="f n -nohook=n k: -key=k U: -uid=U G: -gid=G o: -mount-options=o -ignore-swap -sudo-pwd: -tomb-pwd:"
subcommands_opts[mount]=${subcommands_opts[open]}
+
subcommands_opts[create]="f s: -size=s -force k: -key=k U: -uid=U G: -gid=G -ignore-swap -kdf: -sudo-pwd: -tomb-pwd: -use-urandom"
+
+ subcommands_opts[forge]="f -ignore-swap -kdf: -use-urandom U: -uid=U G: -gid=G"
+ subcommands_opts[dig]="f -ignore-swap s: -size=s"
+
subcommands_opts[passwd]="f -ignore-swap -kdf: -tomb-old-pwd: -tomb-pwd: "
subcommands_opts[close]="-sudo-pwd: U: -uid=U G: -gid=G"
subcommands_opts[help]=""
@@ -1864,6 +2044,16 @@ main() {
check_priv
create_tomb ${=PARAM}
;;
+
+ # new creation in three steps
+ forge)
+ check_priv
+ forge_key ${=PARAM}
+ ;;
+ dig)
+ dig_tomb ${=PARAM}
+ ;;
+
mount|open)
check_priv
mount_tomb $PARAM[1] $PARAM[2]
