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.

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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

N color bytes = N *1/8 message bytes 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.