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 Forum index » Advanced Topics » Cutting edge
psteg - a poor man's steganography
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technosaurus


Joined: 18 May 2008
Posts: 4021
PostPosted: Mon 24 Oct 2011, 17:14    Post_subject:  psteg - a poor man's steganography
Sub_title: A practical use for steganography		  
so, its pretty simple, encrypt a file (optional)
xz it to a container file (jpg, mpg, mov ...)
the regular file will work as normal
to get the hidden file just zcat container > original


This was my original intention:
Quote:

inspired by steganography and the exe icons in windows / ROX-App icons in puppy, here is a package format that looks nice too.

This is how it works (have only tested manually, script to follow)
take a screenshot image (as jpeg)
make your package format is optional at this point (tar.xz is my preference)

get the size of your package:
PKGSIZE=`stat -c %s package`

add the package to the jpg:
cat package >> screenshot.jpg

we will need to know how much data to get later:
printf $PKGSIZE >> screenshot.jpg

crap now we need to now how many bytes that was
printf ${#PKGSIZE} >> screenshot.jpg

That is it for creating it, you should still be able to open it with an image viewer.

But how to get the data?

how many bytes was our info string
BYTESINFO=`tail -c 1 screenshot.jpg`

now we get the string:
STRSIZE=`tail -c $(($BYTESINFO+1)) screenshot.jpg`

but we still have that extra byte
SIZE=${STRSIZE:0:BYTESINFO}

tail -c $(($SIZE+${#STRSIZE})) screenshot.jpg |head -c $SIZE >package

Edit: other things to consider - filename, checksum, default operation
use the good ol' puppy standard separator ...
size|file_name|chcksum|chcksumtype|defaultmode|strlen

edit2: I wrote an sfs linker in jwm_tools that will mount link and autorun an sfs file ... new squash has xz support, so perhaps this would be a better way to go. Click on screenshot, get corresponding screen in ~0.2s (similar to magicermine which is currently proprietary)

Edited_time_total
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technosaurus


Joined: 18 May 2008
Posts: 4021
PostPosted: Wed 26 Oct 2011, 02:30    Post_subject:  
so here is a working example:
Code:
#!/bin/sh
#copyright 2011 Brad Conroy - redistributable under the UIUC license
[ -f "$1" ] && [ -f "$2" ] || exit
SIZE1=`stat -c %s $1`
SIZE2=`stat -c %s $2`
NAME1=${1##*/}
NAME2=${2##*/}
EXT=${1##*.}

cp $1 ${NAME1}_${NAME2}.$EXT
echo "
NAME1=${NAME1} SIZE1=${SIZE1} NAME2=${NAME2} SIZE2=${SIZE2}
" >> ${NAME1}_${NAME2}.$EXT
cat $2 >> ${NAME1}_${NAME2}.$EXT


Code:
#!/bin/sh
#copyright 2011 Brad Conroy - redistributable under the UIUC license
[ $1 ] && [ -f $1 ] || exit
while read LINE; do
case $LINE in
   NAME1=*SIZE1=*NAME2=*SIZE2=*)eval $LINE;break;;
esac
done < $1
[ "${SIZE1}" ] && [ "${NAME1}" ] && [ "${SIZE2}" ] && [ "${NAME2}" ] || exit
head -c ${SIZE1} ${1} > ${NAME1}
tail -c ${SIZE2} ${1} > ${NAME2}


This is a very generic implementation that can also be used as a poor man's steganography using only busybox applets (shell, stat, head and tail)
the first file should be something containerized (so it knows where the end of its data is) and preferably known to have varying sizes jpeg is fine if the second file is small, but avi, mov or mpg if the second file is large

The second file could be anything from text to a heavily encrypted file.

I think I have it broken down into the simplest form for further modification
you may not need to fuss with recovering the container file - if so you can remove the code related to it ... name1 size1 and head portions
if you are trying to hide a file, you may not want to even have the file name included and just have the output defined by the user - also a fairly easy mod
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PANZERKOPF

Joined: 16 Dec 2009
Posts: 264
Location: Earth
PostPosted: Wed 26 Oct 2011, 11:28    Post_subject: Re: jpkg - screenshots as the package format
Sub_title: A practical use for steganography		  
technosaurus wrote:
inspired by steganography

Probably I found another way, without any additional tools.
cat archive.tar.xz >>image.jpg
xzcat image.jpg > archive.tar
Seems xzcat successfully finds a signature (FD377A58h) at the end of "garbage" (mean jpeg's body) and decompresses an archive.
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technosaurus


Joined: 18 May 2008
Posts: 4021
PostPosted: Wed 26 Oct 2011, 12:55    Post_subject:  
nice, maybe instead of catting an xz file, we can just:
xz -cze9 inputfile.tc >> outputfile.mpg

edit: nope, neither way seems to be working - back to my previous example then
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aragon

Joined: 15 Oct 2007
Posts: 1695
Location: Germany
PostPosted: Wed 26 Oct 2011, 14:58    Post_subject:  
http://linux-hacks.blogspot.com/2009/02/theory-behind-hiding-zipped-file-under.html
http://linux-hacks.blogspot.com/2009/02/hiding-zipped-files-under-jpg-images.html

seems to be more simple.

Aragon
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aragon

Joined: 15 Oct 2007
Posts: 1695
Location: Germany
PostPosted: Wed 26 Oct 2011, 15:04    Post_subject:  
a second note: psteg is allready taken by an app from vovchik.

http://www.murga-linux.com/puppy/viewtopic.php?t=57806

aragon
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technosaurus


Joined: 18 May 2008
Posts: 4021
PostPosted: Wed 26 Oct 2011, 15:50    Post_subject:  
steg-osaurus it is then Smile
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DPUP5520

Joined: 16 Feb 2011
Posts: 798
PostPosted: Wed 26 Oct 2011, 16:04    Post_subject:  
There are many great stego programs out there u may want to check out and try such as hide and seek, outguess, snow, diit, and steghide just to name a few.
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technosaurus


Joined: 18 May 2008
Posts: 4021
PostPosted: Wed 26 Oct 2011, 16:23    Post_subject:  
Yes there are, but they all have some limitation that would keep them out of standard puppy (size, dependencies, file limitations ...)

All this needs is a GUI that uses bcrypt which is already included.

The code in /usr/sbin/grub-md5-crypt and bcrypt_gui is a good starting point

The encryption format can be anything though (including none) if bcrypt is replaced.
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technosaurus


Joined: 18 May 2008
Posts: 4021
PostPosted: Wed 26 Oct 2011, 17:02    Post_subject:  
here is the start of a basic gui
Code:
#! /bin/sh
#copyright 2011 Brad Conroy - redistributable under the UIUC license
#todo add bcrypt options, output filename, backup container ...
export MAIN_DIALOG='
<vbox>
   <frame Container Filename>
      <hbox tooltip-text="Select a container file such as: jpg,mpg,avi,mov...">
         <entry accept="filename">
            <label>Select an Existing File</label>
            <variable>CONTAINER_FILENAME</variable>
         </entry>
         <button>
            <input file stock="gtk-open"></input>
            <action type="fileselect">CONTAINER_FILENAME</action>
         </button>
      </hbox>
   </frame>
   <frame Encrypted Filename>
      <hbox tooltip-text="Select the file you wish to encrypt">
         <entry accept="filename">
            <label>Select an Existing File</label>
            <variable>ENCRYPT_FILENAME</variable>
         </entry>
         <button>
            <input file stock="gtk-open"></input>
            <action type="fileselect">ENCRYPT_FILENAME</action>
         </button>
      </hbox>
   </frame>
   <frame Password>
      <entry invisible_char="052" visibility="false">
         <default>woofwoof</default>
         <variable>PASSWORD1</variable>
      </entry>
   </frame>
   <frame Verify Password>
      <entry invisible_char="052" visibility="false">
         <default>woofwoof</default>
         <variable>PASSWORD2</variable>
      </entry>
   </frame>
   <hbox>
    <button ok></button>
    <button cancel></button>
   </hbox>
</vbox>
'

eval `gtkdialog3 --program=MAIN_DIALOG`

[ "$CONTAINER_FILENAME" ] && [ "$ENCRYPT_FILENAME" ] || exit
[  "$PASSWORD1" == "$PASSWORD2" ] || exit

echo "$PASSWORD1
$PASSWORD2" |bcrypt -o "$ENCRYPT_FILENAME" >/tmp/stegosaurus
SIZE=`stat -c %s /tmp/stegosaurus`

echo "
ALLTRANSLATIONSSIZE=${SIZE}
" >> ${CONTAINER_FILENAME}
cat /tmp/stegosaurus >> ${CONTAINER_FILENAME}

yaf-splash -text "complete ${CONTAINER_FILENAME} increased by just over $SIZE"

#for debugging ... this will be in the
#while read A; do case $A in ALLTRANSLATIONSSIZE=*)eval $A && break;;esac;done< ${CONTAINER_FILENAME}
#tail -c $ALLTRANSLATIONSSIZE ${CONTAINER_FILENAME} > ${ENCRYPT_FILENAME}.bfe
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PANZERKOPF

Joined: 16 Dec 2009
Posts: 264
Location: Earth
PostPosted: Thu 27 Oct 2011, 10:16    Post_subject:  
technosaurus wrote:

edit: nope, neither way seems to be working - back to my previous example then

Oops... You are right, unxz fails.

Testing zip/unzip archiver:
cat archive.zip >> image.jpg
unzip image jpg
It works! Just says "Warning! ???? extra bytes at begining..."
Note I used "full" unzip, busybox unzip fails.

Testing arj archiver:
cat archive.arj >> image.jpg
arj e image jpg
Works!
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technosaurus


Joined: 18 May 2008
Posts: 4021
PostPosted: Thu 27 Oct 2011, 16:01    Post_subject:  
http://lists.busybox.net/pipermail/busybox/2008-March/064569.html
We can use tr to do the encryption

And zip files can be password protected, but I may take a look at patching busybox zip first.
Other possibilities: use it to add sfs file to kernel image
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SFR


Joined: 26 Oct 2011
Posts: 770
PostPosted: Tue 29 Oct 2013, 10:09    Post_subject:  
ZIP files indeed have nice possibilities - what about concatenating a fake zip archive (fake = containing some unimportant stuff, a decoy) with a 7zip (preferably encrypted) archive?

Code:
#!/bin/bash

# slip2zip

[ $# -ne 3 ] && { echo "Usage: ${0##*/} <input_zip_file> <input_7z_file> <output_name>"; exit; }

head -c 30 "$1" | cat - "$2" "$1" > "${3}.zip"
zip -A "${3}.zip"


As long as such file has .zip extension, it behaves like zip - "decoy" part can be listed/extracted (only full 'unzip' or 7zip; busybox's fails in this case, too) without any warnings and 'file somearch.zip' reports an ordinary zip file.
Fooling the 'file' utility and lack of warnings is achieved by appending a part of original zip header to the beginning of the file (head -c 30 ...) and adjusting its internal structure (zip -A ...).
After changing the extension to .7z we're gaining access to the "hidden" 7zip part and, suprisingly, 7zip has nothing against those 30 leading, extra bytes.

BTW, to avoid unnecessary suspicions, the size of uncompressed "decoy" part should be greater than the size of concatenated zip+7z, what could be achieved by using high compression level and by including some "sparse" files into it.

Pros: self-containability (no dedicated tool is needed, except generally available (p)7zip) and portability (tested also in Windoze - both parts can be separately accessed using 7zip, IZArc, PeaZip, WinZIP, WinRAR & ZipGenius).

Cons: well, of course closer look (hexdump) or that unfortunate busybox behavior will reveal that something's not quite right.

I have attached an exemplary zip+7z.

Greetings!
example.zip
Description  Change extension to .7z to access "hidden" part.
 zip

 Download 
Filename  example.zip 
Filesize  3.46 KB 
Downloaded  18 Time(s) 

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disciple

Joined: 20 May 2006
Posts: 6316
Location: Auckland, New Zealand
PostPosted: Tue 29 Oct 2013, 16:13    Post_subject:  
It's kind of off topic, but when Flickr came out with their free 1TB my first thought was about how neat it would be to use it as a backup filesystem by zipping files and appending to jpegs. But then I saw that almost as soon as it came out someone had implemented the same idea but hiding the files in pngs instead: https://github.com/Rotten194/flickr-fuse Wink
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technosaurus


Joined: 18 May 2008
Posts: 4021
PostPosted: Tue 29 Oct 2013, 17:59    Post_subject:  
I wouldn't count on that except to share files short term, it is quite possible that they would decide to run image optimizers (optipng, jpegtran,...) or some other craziness on the images that would remove embedded data
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