Steganography

Rayan Ghamri

Introduction

Steganography from the Greek word steganos meaning “covered” and the Greek word graphie meaning “writing”

Steganography is the process of hiding of a secret message within an ordinary message and extracting it at its destination

Anyone else viewing the message will fail to know it contains hidden/encrypted data

Cryptography VS Steganography

Steganography is the science of hiding information in such a way that no one suspects the information exists.

With cryptography the information is known to exist, but it is encoded in such a way that only the intended recipient can read it.

Steganography is usually combined with cryptography.

Continued

Steganography - Carrier Files

bmp

jpeg

gif

wav

mp3

Why Images?

It is the most widely used medium being used today

Takes advantage of our limited visual perception of colors

This field is expected to continually grow as computer graphics power also grows

Many programs are available to apply steganography

Some tools: Steganos

S-Tools (GIF, JPEG)

StegHide (WAV, BMP)

Invisible Secrets (JPEG)

JPHide

Camouflage

Hiderman

And many others…

Why Images..

Digital images are made up of pixels

The arrangement of pixels make up the image’s “raster data”

8-bit and 24-bit images are common

The larger the image size, the more information you can hide.

Why Steganography…

Hiding data is better than moving it shown and encrypted.

To hide data in a popular object that will not attract any attention.

In case the data is extracted, it will be encrypted.

Steganography Techniques

Physical

Printed

Digital (Modern)

Examples in History (Physical)

Tattoos on shaved heads

Wax-covered tablets

Microdots – shrunken pictures

Invisible Inks - milk, fruit juice.

Printed Steganography These messages were sent by the German

embassy in World War I. This is called a null cipher.

PRESIDENT'S EMBARGO RULING SHOULD HAVE IMMEDIATE NOTICE. GRAVE SITUATION AFFECTING INTERNATIONAL LAW. STATEMENT FORESHADOWS RUIN OF MANY NEUTRALS. YELLOW JOURNALS UNIFYING NATIONAL EXCITEMENT IMMENSELY.

APPARENTLY NEUTRAL'S PROTEST IS THOROUGHLY DISCOUNTED AND IGNORED. ISMAN HARD HIT. BLOCKADE ISSUE AFFECTS PRETEXT FOR EMBARGO ON BYPRODUCTS, EJECTING SUETS AND VEGETABLE OILS.

Taking the first letter in each word of message 1 or second letter in message 2 reveals the hidden text.

PERSHING SAILS FROM NY JUNE 1.

Digital Steganography

Modern digital steganography data is encrypted then inserted and hidden, using a special algorithm which

may add and/or modify the contents of the file This technique may simply append the data to the file, or

disperse it throughout Carefully crafted programs apply the encrypted data such

that patterns appear normal.

Example:Left image is original JPEG file

Right image is with hidden message

Methods for hiding data in Digital Image:

Least significant bit (LSB)

Discrete Cosine Transform (DCT)

Least significant bit (LSB)

Replaces least significant bits with the message to be encoded

Most popular technique when dealing with images

Simple, but susceptible to lossy compression and image manipulation

Example for LSB The simplest and most common type of steganography

is LSB (least significant bit). The one’s bit of a byte is used to encode the hidden information.

Suppose we want to encode the letter A (ASCII 65 or binary 01000001) in the following 8 bytes of a carrier file.

01011101 11010000 00011100 10101100

11100111 10000111 01101011 11100011

becomes

01011100 11010001 00011100 10101100

11100110 10000110 01101010 11100011

RGB Color Model in Image Files red, green, and blue light are

added together in various ways to reproduce a broad array of colors.

(0, 0, 0) is black (255, 255, 255) is white (255, 0, 0) is red (0, 255, 0) is green (0, 0, 255) is blue (255, 255, 0) is yellow (0, 255, 255) is cyan (255, 0, 255) is magenta

Encoding Process

Step 1:

Convert image to pixels. Then these pixels split to R, G and B bytes

Step 2:

In this step secret message is converted to bytes.

Step 3:

Actual data hiding occurs when each bit of secret message is inserted to least significant bit of color byte. So one byte of message is inserted in 8 color bytes. By using this formula

N color bytes = N *1/8 message bytes

Example..

Example..

Methods of detecting

Visual Detection (JPEG, BMP, GIF, etc.) Audible Detection (WAV, MPEG, etc.) Structural Detection - View file properties/contents

size difference date/time difference

Decoding algorithm

Finally..

Steganography as a whole has existed in many forms throughout much of history.

Lossless compression of images with a great deal of color variation work best as a cover image to embed a message.

Steganography can be used as benefitial tool for privacy.