16-11-2012, 04:17 PM
CPSC 350 Data Structures: Image Steganography
ImageSteganography.pdf (Size: 249.33 KB / Downloads: 714)
Introduction
Steganography is the process of hiding a secret message within a larger one in
such a way that someone cannot know the presence or contents of the hidden
message. Although related, Steganography is not to be confused with Encryption,
which is the process of making a message unintelligible—Steganography attempts to
hide the existence of communication.
The basic structure of Steganography is made up of three components: the
“carrier”, the message, and the key1. The carrier can be a painting, a digital image, an
mp3, even a TCP/IP packet among other things. It is the object that will ‘carry’ the
hidden message. A key is used to decode/decipher/discover the hidden message.
This can be anything from a password, a pattern, a black-light, or even lemon juice.
In this paper I will focus on the use of Steganography within digital images (BMP
and PNG) using LSB Substitution, although the properties of Image Steganography
may be substituted with audio mp3’s, zip archives, and any other digital document
format relatively easily.
In-Depth Discussion
When first deciding what topic to research and study I was initially interested in
encryption algorithms and ciphers. I have always been intrigued with security
implementation and breaching, so I began developing an encryption algorithm to
test its strength. Soon, with the help of some friends, I discovered Image
Steganography and it only seemed natural that I take my encryption algorithm and
apply it to the newfound subject. Further research, development, and intrigue led to
me to develop attacks on Image Steganography (attempting to discover if an image
has Steganography applied to it).
Applications
Image Steganography has many applications, especially in today’s modern, hightech
world. Privacy and anonymity is a concern for most people on the internet.
Image Steganography allows for two parties to communicate secretly and covertly. It
allows for some morally-conscious people to safely whistle blow on internal actions;
it allows for copyright protection on digital files using the message as a digital
watermark. One of the other main uses for Image Steganography is for the
transportation of high-level or top-secret documents between international
governments. While Image Steganography has many legitimate uses, it can also be
quite nefarious. It can be used by hackers to send viruses and trojans to compromise
machines, and also by terrorists and other organizations that rely on covert
operations to communicate secretly and safely2.
Implementation
There are currently three effective methods in applying Image Steganography:
LSB Substitution, Blocking, and Palette Modification1. LSB (Least Significant Bit)
Substitution is the process of modifying the least significant bit of the pixels of the
carrier image. Blocking works by breaking up an image into “blocks” and using
Discrete Cosine Transforms (DCT). Each block is broken into 64 DCT coefficients that
approximate luminance and color—the values of which are modified for hiding
messages. Palette Modification replaces the unused colors within an image’s color
palette with colors that represent the hidden message.1