Steganographer

A command line tool that lets you hide one file into another

Table of Contents

1. Introduction
2. What it does
3. Dependencies
4. Installation
5. Usage
6. Uninstall

Introduction

Steganography is the practice of concealing messages and information within other non-secret text or data. The necessity to conceal information can be traced back millenia, and has played an important role throughout history, moreso in times where keeping something from prying eyes is much harder. One way to hide a message is to use some method of encryption, effectively rendering the information useless to a person who wouldn't know how to reverse the process. This method (called cryptography), however, usually results in unintelligible information which makes it obvious that a secret is hidden within the sequence present.

The problem can be avoided by using another way to hide information: hiding it in plain sight. This approach is greatly facilitated by the usage of computers. As all information consists of streams of bytes, it is possible to alter the least significant bit of each one in a way that they store a hidden message. For example, altering the least significant bit in a pixel of an image file wouldn't not lead to difference noticeable to the human eye, but would allow to store one binary bit of hidden information.

What it does

image with hidden message (left) and the message recovered (right)

In order to hide information this program replaces a set amount of least significant bits (LSBs) of a cover image with an equal number of most significant bits (MSBs) of a secret image. Unavoidably, information related to the images is lost during the process. To increase the quality of the hidden image we need to replace a higher number of LSBs in the cover, but the more bits we replace the more visible the contrast between the cover and the secret becomes. A balance must be struck in order to hide the secret effectively and not render the hiding process pointless.

Dependencies

Functionality has only been verified on a Linux system (Ubuntu 18.04) The program uses libpng for the PNG images' I/O operations. As far as I can tell, there shouldn't be any other requirement to compile and run.

Installation

First you must obtain the source code and navigate to the directory. You can quickly do this by cloning this repository using its url using the following command:

git clone https://github.com/BAlexandros/Steganographer && cd Steganographer

Now you must compile the source code. This can be done using the supplied Makefile, or manually if you wish. If you want to use the Makefile, you have to be in the parent directory of the project and run one of the following commands:

• make will simply create a steganize executable in the current directory

• make install will create a steganize executable in the /bin directory, so it may require root permissions

Usage

The program can be run with the ./steganize command from the local directory, or just steganize if you used make install.

I've tried my best to give a descriptive help message to the tool, which can be viewed if you run the program without any arguments, or with the help flag (-h or --help)

The main usage of the tool is as follows:

steganize -e /path/to/cover/file.png /path/to/secret/file.png

This will hide the secret file (/path/to/secret/file.png) into the cover file (/path/to/cover/file.png) and write the result to a file named out.png.

To recover a hidden image from another image, use the -d flag:

steganize -d /path/to/combined/file.png

This will create a file named out.png which contains the hidden image.

The -o flag can be used in either case to change the output file name. For example:

steganize -d /path/to/combined/file.png -o /path/to/output/file.png

An important flag is the significant bits flag -s. The number following this flag determines the number of LSBs that will be replaced in the cover image and MSBs that will be kept from the secret. For example:

steganize -e file1.png file2.png -s 2

The above command would replace the 2 LSBs from file1.png with the 2 MSBs from file2.png The default number of significant bits is 4.

Note: If you use the -s flag when combining two files, you will have to use it again (and supply it with the same argument) in order to properly recover the image with the -b flag.

Uninstall

To either remove part of, or the entire program, you have the following options:

• make clean will remove the executable from the current directory

• make uninstall will remove the executable from the /bin directory (might require root permissions)

• make allclean will remove all the source files and executables related to the program (may need root permissions if make install was used). Using this command means that you would have to repeat the installation to use the tool again.

The images used were taken from https://www.pexels.com