Steganography Toolkit

This project is a Docker image useful for solving Steganography challenges as those you can find at CTF platforms like hackthebox.eu. The image comes pre-installed with many popular tools (see list below) and several screening scripts you can use check simple things (for instance, run check_jpg.sh image.jpg to get a report for a JPG file).

Usage

First make sure you have Docker installed (how to). Then you can use the shell scripts bin/build.sh and bin/run.sh in this repo to build the image and run the container. You will be dropped into a bash shell inside the container. It will have the data folder mounted, into which you can put the files to analyze.

If you don't use the scripts, follow these steps:

1. Build image (docker build -t <image_name> .) or pull from Docker hub (docker pull dominicbreuker/stego-toolkit)
2. Start a container with your files mounted to the folder /data (docker run -it <image_name> -v /local/folder/with/data:/data /bin/bash)
3. Use CLI tools and screening scripts on your files: e.g., run check_jpg.sh image.jpg to create a quick report, or run brute_jpg.sh image.jpg wordlist.txt to try extracting hidden data with various tools and passwords
4. If you want to run GUI tools use one of these two ways:

• Run start_ssh.sh and connect to your container with X11 forwarding
• Run start_vnc.sh and connect to the container's Desktop through your browser

Check out the following sections for more information:

• What tools are installed? Go here
• What scripts can I run to quickly screen files automatically or brute force them? Go here
• How can I play with different Steganography examples to see if I can break them? Go here
• How can I run GUI tools inside the container? go here

Demo

Start with docker run -it --rm -v $(pwd)/data:/data dominicbreuker/stego-toolkit /bin/bash. You will be dropped into a container shell in work dir /data. Your host folder $(pwd)/data will be mounted and the images inside will be accessible.

Tools

Many different Linux and Windows tools are installed. Windows tools are supported with Wine. Some tools can be used on the command line while others require GUI support!

Command line interface tools

These tools can be used on the command line. All you have to do is start a container and mount the steganography files you want to check.

General screening tools

Tools to run in the beginning. Allow you to get a broad idea of what you are dealing with.

Tools detecting steganography

Tools designed to detect steganography in files. Mostly perform statistical tests. They will reveal hidden messages only in simple cases. However, they may provide hints what to look for if they find interesting irregularities.

Tools actually doing steganography

Tools you can use to hide messages and reveal them afterwards. Some encrypt the messages before hiding them. If they do, they require a password. If you have a hint what kind of tool was used or what password might be right, try these tools. Some tools are supported by the brute force scripts available in this Docker image.

Steganography GUI tools

All tools below have graphical user interfaces and cannot be used through the command line. To run them, you must make an X11 server available inside the container. Two ways are supported:

• run start_ssh.sh to fire up an SSH server. Connect afterwards with X11 forwarding. Requires an X11 server on your host!
• run start_vnc.sh to fire up a VNC server + client. Connect afterwards with your browser to port 6901 and you get an Xfce desktop. No host dependencies!

Alternatively, find other ways to make X11 available inside the container. Many different ways are possible (e.g., mount UNIX sockets).

Screening scripts

Many tools above do not require interaction with a GUI. Therefore, you can easily automate some workflows to do basic screening of files potentially containing hidden messages. Since the applicable tools differ by filet type, each file type has different scripts.

For each file type, there are two kinds of scripts:

• XXX_check.sh <stego-file>: runs basic screening tools and creates a report (+ possibly a directory with reports in files)
• XXX_brute.sh <stego-file> <wordlist>: tries to extract a hidden message from a stego file with various tools using a wordlist (cewl, john and crunch are installed to generate lists - keep them small).

The following file types are supported:

• JPG: check_jpg.h and brute_jpg.sh (brute running steghide, outguess, outguess-0.13, stegbreak, stegoveritas.py -bruteLSB)
• PNG: check_png.h and brute_png.sh (brute running openstego and stegoveritas.py -bruteLSB)

Wordlist generation

The brute forcing scripts above need wordlists. Imho it will very likely not help to use huge standard wordlists like rockyou. The scripts are too slow for it and stego challenges seem to not be designed for this. A more probable scenario is that you have a hunch what the password could be but you do not know exactly.

For these cases, several tools to generate wordlists are included:

• john: the community enhanced version of John the Ripper can expand your wordlists. Create a base wordlist with a few candidate passwords and use john to create many variants of them. Use john -wordlist:/path/to/your/wordlist -rules:Single -stdout > /path/to/expanded/wordlist to apply extensive rules (~x1000) john -wordlist:/path/to/your/wordlist -rules:Wordlist -stdout > /path/to/expanded/wordlist for a reduced ruleset (~x50).
• crunch: can generate small wordlists if you have a pattern in mind. For instance, if you know the passwords ends with 1984 and is 6 letters long, use crunch 6 6 abcdefghijklmnopqrstuvwxyz -t @@1984 will generate the 26 * 26 = 676 passwords aa1984, ab1984, ... up to zz1984. The format is crunch <min-length> <max-length> <charset> <options> and we used the templating option. Check out less /usr/share/crunch/charset.lst to see the char sets crunch ships with.
• CeWL: can generate wordlists if you know a website is related to a password. For instance, run cewl -d 0 -m 8 https://en.wikipedia.org/wiki/Donald_Trump if you suspect a picture of Donald Trump contains an encrypted hidden message. The command scrapes the site and extracts strings at least 8 characters long.

Steganography examples

The image contains a sample image and audio file each in different formats:

• /examples/ORIGINAL.jpg
• /examples/ORIGINAL.png
• /examples/ORIGINAL.mp3
• /examples/ORIGINAL.wav

It also contains a script /examples/create_examples.sh which you can run to embed a hidden message ("This is a very secret message!") into these files with many different methods. After running this script, you find these files in /examples/stego-files with their names indicating which tool was used to embed the message. You can run the screening scripts to see if they find anything on them or try to break them otherwise.

GUI and Containers

By default, no GUI tools can be run in a Docker container as no X11 server is available. To run them, you must change that. What is required to do so depends on your host machine. If you:

• run on Linux, you probably have X11
• run on Mac OS, you need Xquartz (brew install Xquartz)
• run on Windows, you have a problem

Use X11 forwarding through SSH if you want to go this way. Run start_ssh inside the container to start the server, make sure you expose port 22 when starting the container: docker run -p 127.0.0.1:22:22 ..., then use ssh -X ... when connecting (the script prints the password).

To not depend on X11, the image comes with a TigerVNC server and noVNC client. You can use it to open an HTML5 VNC session with your browser to connect to the containers Xfce desktop. To to that, run start_vnc.sh inside the container to start server and client, make sure you expose port 6901 when starting the container docker run -p 127.0.0.1:6901:6901 ... and go to localhost:6901/?password=<the_password> (the script prints the password).

Using SSH with X11 forwarding

Commands in the GIF for copy & paste:

# in 1st host shell
docker run -it --rm -p 127.0.0.1:22:22 dominicbreuker/stego-toolkit /bin/bash

# inside container shell
start_ssh.sh

# in 2nd host shell (use it to launch GUI apps afterwards)
ssh -X -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no root@localhost

Using Browser and VNC

Commands in the GIF for copy & paste:

# in 1st host shell
docker run -it --rm -p 127.0.0.1:6901:6901 dominicbreuker/stego-toolkit /bin/bash

# inside container shell
start_vnc.sh

# in browser, connect with: http://localhost:6901/?password=<password_from_start_vnc>

Link collection

This is a collection of useful Steganography links:

• You must be able to spot codes. Check out this cheat sheet from Eric Harshbarger, which contains many different codes.
• Cheat sheet describing workflows, things to look for and common tools: click
• Forensics CTF guide with lots of ideas for stego challenges: click
• File format descriptions as beautiful posters: click

References

The following example media files are included in this repository:

• Demo image (JPG, PNG): https://pixabay.com/p-1685092
• Demo sound file (MP3, WAV): https://upload.wikimedia.org/wikipedia/commons/c/c5/Auphonic-wikimedia-test-stereo.ogg --- By debuglevel (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons