tfixes to piping keys stdin/out in image steganography - tomb - the crypto undertaker
HTML git clone git://parazyd.org/tomb.git
DIR Log
DIR Files
DIR Refs
DIR README
DIR LICENSE
---
DIR commit 534476a84988dc08ac1c7678d74651b880306aba
DIR parent b7e89e52466a444a2e5c199217733f0bcf38e197
HTML Author: Jaromil <jaromil@dyne.org>
Date: Tue, 5 Aug 2014 17:05:49 +0200
fixes to piping keys stdin/out in image steganography
Also started refactoring code around key handling and
added some documentation.
Diffstat:
M tomb | 264 ++++++++++++++++++++++---------
1 file changed, 192 insertions(+), 72 deletions(-)
---
DIR diff --git a/tomb b/tomb
t@@ -539,30 +539,34 @@ check_bin() {
# operations. On success returns 0 and prints out the full path to
# the key.
load_key() {
- # take the name of a tomb file as argument
- if option_is_set -k ; then
- if [[ "`option_value -k`" == "-" ]]; then
- _verbose "load_key reading from stdin."
- # take key from stdin
- tombkeydir=`safe_dir load_key_stdin` # global used to check if key from stdin
- _verbose "tempdir is $tombkeydir"
- act "Waiting for the key to be piped from stdin... "
- cat > ${tombkeydir}/stdin.tmp.key
- print ok >&2
- tombdir=${tombkeydir}
- tombfile=stdin.tmp.key
- tombname="stdin"
- elif [[ "`option_value -k`" != "" ]]; then
- _verbose "load_key argument: `option_value -k`"
- # take key from a file
- tombkey=`option_value -k`
- tombdir=`dirname $tombkey`
- tombfile=`basename $tombkey`
- fi
+ # take the name of a tomb file as argument to option -k
+ # if no argument is given, tomb{key|dir|file} are set by caller
- else # no -k specified
+ { option_is_set -k } || {
_failure "This operation requires a key file to be specified using the -k option."
- return 1
+ return 1 }
+
+ local keyopt
+ keyopt="`option_value -k`"
+
+ if [[ "$keyopt" == "-" ]]; then
+ _verbose "load_key reading from stdin."
+ # take key from stdin
+ tombkeydir=`safe_dir load_key_stdin`
+ # tombkeydir is a global used to check if key from stdin
+ _verbose "tempdir is $tombkeydir"
+ act "Waiting for the key to be piped from stdin... "
+ cat > ${tombkeydir}/stdin.tmp.key
+ print ok >&2
+ tombdir=${tombkeydir}
+ tombfile=stdin.tmp.key
+ tombname="stdin"
+ elif [[ "$keyopt" != "" ]]; then
+ _verbose "load_key argument: `option_value -k`"
+ # take key from a file
+ tombkey=`option_value -k`
+ tombdir=`dirname $tombkey`
+ tombfile=`basename $tombkey`
fi
tombkey=${tombdir}/${tombfile}
t@@ -573,16 +577,59 @@ load_key() {
drop_key
return 1 }
- # this does a check on the file header
- if ! is_valid_key ${tombkey}; then
- _warning "The key seems invalid, the application/pgp header is missing."
- drop_key
- return 1
- fi
+ # TODO: move this condition for JPEG steg into is_valid_key
+ [[ `file "$tombkey"` =~ "JP.G" ]] || {
+ # if the key file is an image don't check file header
+ if ! is_valid_key ${tombkey}; then
+ _warning "The key seems invalid or its format is not known by this version of Tomb."
+ drop_key
+ return 1
+ fi
+ }
+
print "$tombkey"
return 0
}
+# takes two args just like get_lukskey
+# prints out the decrypted content
+# contains tweaks for different gpg versions
+gpg_decrypt() {
+ # fix for gpg 1.4.11 where the --status-* options don't work ;^/
+ gpgver=`gpg --version --no-permission-warning | awk '/^gpg/ {print $3}'`
+ local lukspass="$1"
+ local keyfile="$2"
+
+ if [ "$gpgver" = "1.4.11" ]; then
+ _verbose "GnuPG is version 1.4.11 - adopting status fix."
+
+ print "$lukspass" | \
+ gpg --batch --passphrase-fd 0 --no-tty --no-options \
+ -d "${keyfile}"
+ ret=$?
+ unset lukspass
+
+ else # using status-file in gpg != 1.4.11
+
+ res=`safe_filename lukskey`
+ [[ $? = 0 ]] || {
+ unset lukspass;
+ _failure "Fatal error creating temp file." }
+
+ print "$lukspass" | \
+ gpg --batch --passphrase-fd 0 --no-tty --no-options \
+ --status-fd 2 --no-mdc-warning --no-permission-warning \
+ --no-secmem-warning -d "${keyfile}" 2> $res
+
+ unset lukspass
+ grep 'DECRYPTION_OKAY' $res > /dev/null
+ ret=$?; rm -f $res
+
+ fi
+ return $ret
+
+}
+
# This function asks the user for the password to use the key it tests
# it against the return code of gpg on success returns 0 and prints
# the password (be careful about where you save it!)
t@@ -604,7 +651,7 @@ ask_key_password() {
return 1
fi
- get_lukskey "$tombpass" "$tombkey" >/dev/null
+ check_lukskey "$tombpass" "$tombkey"
if [ $? = 0 ]; then
passok=1; _message "Password OK."
t@@ -617,7 +664,7 @@ ask_key_password() {
tombpass="$2"
_verbose "ask_key_password with tombpass: $tombpass"
- get_lukskey "$tombpass" "$tombkey" >/dev/null
+ check_lukskey "$tombpass" "$tombkey"
if [ $? = 0 ]; then
passok=1; _message "Password OK."; fi
t@@ -742,55 +789,100 @@ print "-----END PGP MESSAGE-----"
}
+# This function checks if the password effectively works to decrypt
+# the key. It is used by the password prompt to verify validity and
+# it resembles get_lukskey(). 1st arg the password, 2nd the keyfile
+check_lukskey() {
+ local lukspass="$1"
+ local keyfile="$2"
+ local exhumedkey
+
+ firstline=`head -n1 $keyfile`
+ _verbose "check_lukskey XXX $keyfile"
+
+
+ # key is KDF encoded
+ if [[ $firstline =~ '^_KDF_' ]]; then
+ _verbose "KDF: `cut -d_ -f 3 <<<$firstline`"
+ case `cut -d_ -f 3 <<<$firstline` in
+ pbkdf2sha1)
+ pbkdf2_param=`cut -d_ -f 4- <<<$firstline | tr '_' ' '`
+ lukspass=$(tomb-kdb-pbkdf2 ${=pbkdf2_param} 2> /dev/null <<<$lukspass)
+ ;;
+ *)
+ _failure "No suitable program for KDF `cut -f 3 <<<$firstline`."
+ unset lukspass
+ return 1
+ ;;
+ esac
+
+ # key needs to be exhumed from an image
+ elif [[ `file "$keyfile"` =~ "JP.G" ]]; then
+ exhumedkey="`safe_filename exhumedkey`"
+ _verbose "lukspass in check_lukskey: $lukspass"
+
+ exhume_key "$keyfile" "$lukspass" "$exhumedkey"
+ keyfile="$exhumedkey"
+ fi
+ _verbose "lukspass in check_lukskey: $lukspass"
+
+ # check validity, eventually repair adding headers
+ is_valid_key "$keyfile" || {
+ _failure "This key is unusable: $keyfile" }
+
+ # prints out decrypted content to stdout
+ gpg_decrypt "$lukspass" "$keyfile" > /dev/null
+ ret="$?"
+ _verbose "check_lukskey returns $ret"
+ return $ret
+}
+
+
# Gets a key file and a password, prints out the decoded contents to
# be used directly by Luks as a cryptographic key
get_lukskey() {
# $1 is the password, $2 is the keyfile
- local tombpass=$1
- local keyfile=$2
+ local lukspass="$1"
+ local keyfile="$2"
+ local exhumedkey
+
firstline=`head -n1 $keyfile`
_verbose "get_lukskey XXX $keyfile"
+
+ # key is KDF encoded
if [[ $firstline =~ '^_KDF_' ]]; then
_verbose "KDF: `cut -d_ -f 3 <<<$firstline`"
case `cut -d_ -f 3 <<<$firstline` in
pbkdf2sha1)
pbkdf2_param=`cut -d_ -f 4- <<<$firstline | tr '_' ' '`
- tombpass=$(tomb-kdb-pbkdf2 ${=pbkdf2_param} 2> /dev/null <<<$tombpass)
+ lukspass=$(tomb-kdb-pbkdf2 ${=pbkdf2_param} 2> /dev/null <<<$lukspass)
;;
*)
_failure "No suitable program for KDF `cut -f 3 <<<$firstline`."
- unset tombpass
+ unset lukspass
return 1
;;
esac
- fi
- # fix for gpg 1.4.11 where the --status-* options don't work ;^/
- gpgver=`gpg --version | awk '/^gpg/ {print $3}'`
- if [ "$gpgver" = "1.4.11" ]; then
- _verbose "GnuPG is version 1.4.11 - adopting status fix."
+ # key needs to be exhumed from an image
+ elif [[ `file "$keyfile"` =~ "JP.G" ]]; then
+ exhumedkey="`safe_filename exhumedkey`"
+ _verbose "lukspass in get_lukskey: $lukspass"
- print ${tombpass} | \
- gpg --batch --passphrase-fd 0 --no-tty --no-options -d "${keyfile}"
- ret=$?
- unset tombpass
-
- else # using status-file in gpg != 1.4.11
-
- res=`safe_filename lukskey`
- { test $? = 0 } || { unset tombpass; _failure "Fatal error creating temp file." }
+ exhume_key "$keyfile" "$lukspass" "$exhumedkey"
+ keyfile="$exhumedkey"
+ fi
+ _verbose "lukspass in get_lukskey: $lukspass"
- print ${tombpass} | \
- gpg --batch --passphrase-fd 0 --no-tty --no-options --status-fd 2 \
- --no-mdc-warning --no-permission-warning --no-secmem-warning \
- -d "${keyfile}" 2> $res
+ # check validity, eventually repair adding headers
+ is_valid_key "$keyfile" || {
+ _failure "This key is unusable: $keyfile" }
- unset tombpass
- grep 'DECRYPTION_OKAY' $res > /dev/null
- ret=$?; rm -f $res
+ # prints out decrypted content to stdout
+ gpg_decrypt "$lukspass" "$keyfile"
- fi
+ ret="$?"
_verbose "get_lukskey returns $ret"
return $ret
}
t@@ -849,10 +941,13 @@ gen_key() {
fi
# --kdf takes one parameter: iter time (on present machine) in seconds
local -i microseconds
- microseconds=$((itertime*10000))
+ microseconds=$(( itertime * 10000 ))
_success "Using KDF, iterations: $microseconds"
+ _message "generating salt"
pbkdf2_salt=`tomb-kdb-pbkdf2-gensalt`
+ _message "calculating iterations"
pbkdf2_iter=`tomb-kdb-pbkdf2-getiter $microseconds`
+ _message "encoding the password"
# We use a length of 64bytes = 512bits (more than needed!?)
tombpass=`tomb-kdb-pbkdf2 $pbkdf2_salt $pbkdf2_iter 64 <<<"${tombpass}"`
t@@ -904,6 +999,12 @@ bury_key() {
_success "Encoding key $tombkey inside image $imagefile"
_message "Please confirm the key password for the encoding"
+ # We ask the password and test if it is the same encoding the
+ # base key, to insure that the same password is used for the
+ # encryption and the steganography. This is a standard enforced
+ # by Tomb, but its not strictly necessary (and having different
+ # password would enhance security). Nevertheless here we prefer
+ # usability.
if option_is_set --tomb-pwd; then
tomb_pwd="`option_value --tomb-pwd`"
t@@ -940,20 +1041,36 @@ bury_key() {
return $res
}
+
+# mandatory 1st arg: the image file where key is supposed to be
+# optional 2nd arg: the password to use (same as key, internal use)
+# optional 3rd arg: the key where to save the result (- for stdout)
exhume_key() {
- tombkey="`option_value -k`"
- { test "$tombkey" = "" } && {
- tombkey="-"
- _message "printing exhumed key on stdout"
- }
imagefile="$1"
res=1
- file $imagefile | grep -i JPEG > /dev/null
- if [ $? != 0 ]; then
- _failure "Encode failed: $imagefile is not a jpeg image."
- fi
+ knownpass="$2"
+
+ tombkey="$3"
+ [[ "$tombkey" = "" ]] && {
+ tombkey="`option_value -k`"
+ { test "$tombkey" = "" } && {
+ # no key output specified: fallback to stdout
+ tombkey="-"
+ _message "printing exhumed key on stdout" }
+ }
+
+ [[ `file "$imagefile"` =~ "JP.G" ]] || {
+ _failure "Encode failed: $imagefile is not a jpeg image." }
+
+ # when a password is passed as argument then always print out
+ # the exhumed key on stdout without further checks (internal use)
+ { test "$knownpass" = "" } || {
+ steghide extract -sf "$imagefile" -p "$knownpass" -xf -
+ { test $? = 0 } || {
+ _failure "Wrong password or no steganographic key found" }
+ }
{ test "$tombkey" = "-" } || {
if [[ -e "$tombkey" ]]; then
t@@ -1448,6 +1565,7 @@ mount_tomb() {
local tombfile
local tombdir
local tombname
+ local tombpass
tombfile=`basename ${1}`
tombdir=`dirname ${1}`
# check file type (if its a Luks fs)
t@@ -1460,7 +1578,7 @@ mount_tomb() {
_verbose "Tomb found: ${tombdir}/${tombfile}"
# load_key called here
- tombkey=`load_key ${tombdir}/${tombfile}`
+ tombkey=`load_key`
{ test $? = 0 } || {
_failure "Aborting operations: error loading key $tombkey" }
t@@ -1519,7 +1637,10 @@ mount_tomb() {
mapper="tomb.${tombname}.${mapdate}.`basename $nstloop`"
_verbose "dev mapper device: $mapper"
_verbose "Tomb key: $tombkey"
- keyname=`basename $tombkey | cut -d. -f1`
+
+ # take the name only, strip extensions
+ keyname=${tombkey%%.*}
+ _verbose "Tomb name: $keyname (to be engraved)"
if option_is_set --tomb-pwd; then
tomb_pwd="`option_value --tomb-pwd`"
t@@ -1535,7 +1656,6 @@ mount_tomb() {
get_lukskey "${tombpass}" ${tombkey} | \
cryptsetup --key-file - luksOpen ${nstloop} ${mapper}
-
# key dropped here
drop_key
unset tombpass
t@@ -1748,8 +1868,8 @@ list_tombs() {
for h in ${mounted_hooks}; do
print -n "$fg_no_bold[green]$tombname"
print -n "$fg_no_bold[white] hooks "
-# print -n "$fg_bold[white]`basename ${h[(ws:;:)1]}`"
-# print -n "$fg_no_bold[white] on "
+# print -n "$fg_bold[white]`basename ${h[(ws:;:)1]}`"
+# print -n "$fg_no_bold[white] on "
print "$fg_bold[white]${h[(ws:;:)2]}$fg_no_bold[white]"
done
done
t@@ -2019,7 +2139,7 @@ resize_tomb() {
tombname=${tombfile%%\.*}
# load key from options or file
- local tombkey="`load_key ${tombdir}/${tombfile}`"
+ local tombkey="`load_key`"
# make sure to call drop_key later
{ test -r "$tombkey" } || {
_failure "Aborting operations: key not found, use -k" }