Steganography Michel Tannoury December 2019 IPD week 

Steganography Outline -40 Definition History Cryptography vs Steganography Least Significant Bit Steganography Audio and video Steganography 01 02 03 04 05 Steganalysis 06 

What is Steganography? Definition • Steganography comes from the combination of two Greek words: Steganos (στεγᾰνός) : concealed Graphe (γραφή) : writing • It is the practice of concealing a file, message, image, or video within another file, message, image, audio, or video. • Steganography, relies on the imperfection of the human auditory and visual systems. • Data hidden in plain sight! 

Implementation of steganography Hidden Data Cover Medium Stego Key Stego Medium • Stego Medium and Cover medium are of the same type. • 4 ways to implement Steganography: • Text • Images • Audio • Video 

Applications in today’s life -40 Watermarking to protect the copyrights Tag notes to digital images Maintain the confidentiality of valuable data Protection against data alteration 01 02 03 04 

History The sender would shave the head of a servant, write the message, wait till the servant’s hair has regrown and then send him to the destination. Ancient Greece Send a warning about a forthcoming attack to Greece by writing it directly on the wooden backing of a wax tablet before applying its beeswax surface. Sparta Using invisible ink (vinegar, fruit juice, milk, …). The receiver used heat to view what was what hidden on the paper. Europe Ave Maria cipher. 384 columns of letters of the alphabet, each with a corresponding code w ord Germany 440 BC 510-491 BC World war II Renaissance 

History • For example, if you want to send the word monk, it will be Rector gloriosus mansionem immortalem. • Anyone intercepting the message would think it is a prayer, meaning it is unlikely to attract suspicion. 

Cryptography vs Steganography • Cryptography: technique used to make messages meaningless to anyone who doesn’t have the correct key to decrypt them. • Symmetric / Asymmetric encryption. 

Cryptography vs Steganography • Cryptography is strong enough to hide data that is being transmitted. • However, the attacker will know that some sort of secret communication is taking place between the 2 parties. • On the other hand, Steganography allows the sender and receiver to exchange secret data hidden inside ordinary data without rising suspicions. 

Cryptography vs Steganography • In many countries, cryptography is against the law. • Some of the countries that restrict importing cryptography technology: Belarus, Iraq, Mongolia, Myanmar, Russia, Turkmenistan, Uzbekistan. • Cybercriminals and terrorists are using steganography to avoid being caught with cryptography technologies. 

Steganography Algorithm Three parameters should be taken into consideration: The amount of data that can be hidden without significantly changing the cover medium Capacity The resistance for possible modification or destruction in unseen data Robustness Does not raise any suspicion of eavesdroppers Invisibility 

LSB Steganography 154 An image is composed of pixels Zoom 1543*1203 =1856229 pixels 

LSB Steganography - Each pixel contains information about three colors : Red, Green and Blue (RGB) - Each color requires 8 bits (1 byte) - Each pixel requires 24 bits (3 bytes) to specify its color - Example: 11000100 Most significant bit Least significant bit 

LSB Steganography 255 => 1111 1111 254 => 1111 1110 Changing the least significant bit will have invisible effect on the color Changing the least significant bit 

LSB Steganography 255 => 1111 1111 127 => 0111 1111 Changing the most significant bit will have a visible effect on the color Changing the most significant bit 

LSB Steganography Changing the least significant bit will have an invisible effect on the pixel’s color Changing the most significant bit 11111111 11111111 11111111 11111110 11111110 11111110 

LSB Steganography - LSB Steganography is based on overwriting the bit with the lowest arithmetic value. - The least significant bits of the R G B colors of a pixel of a visible image are replaced by bits of the hidden image. RED: 233 => 11101001 Green: 205 => 11001101 Blue: 166 => 10100110 

LSB Steganography - In every pixel, we can hide 3 bits. - Let’s say we want to hide the letter M inside an image. - We need to explain first ASCII code: - It is a code for representing 128 English characters as numbers, with each letter assigned a number from 0 to 127. - For example, the ASCII code for uppercase M is 77. - Most computers use ASCII codes to represent text, which makes it possible to transfer data from one computer to another. - M => 77 => 0100 1101 - We have 8 bits to hide => we need 3 pixels (as each pixel can hide 3 bits) 

LSB Steganography - Original photo first three pixels value: Pixel Red Green Blue 1 156 => 10011100 155 => 10011011 150 => 10010110 2 157 => 10011101 156 => 10011100 151 => 10010111 3 160 => 10100000 159 => 10011111 154 => 10011010 - M => 77 => 0100 1101 - Photo first three pixels after hiding letter M Pixel Red Green Blue 1 156 => 10011100 155 => 10011011 150 => 10010110 2 157 => 10011100 156 => 10011101 151 => 10010111 3 160 => 10100000 159 => 10011111 154 => 10011010 

LSB Steganography • In LSB, the least significant bit of each pixel for a specific color channel or for all color channels is replaced with a bit from the secret data. • The probability of detecting the hidden data is high. • Algorithms were developed to make detection of hidden data harder. 

LSB Steganography Clean image of the snail Stego image of the snail 

LSB Steganography • How much data can we hide in an image using LSB Steganography? • The answer depends on the algorithm we are using and the total change to the image that is acceptable. • Let’s say we have an image composed of 1024*768 pixels = 786432 pixels • Each pixel can hide 3 bits (if we are using the last bit of R, G, and B). • Total = 2359296 bits = 288 Kbytes 

Demonstration • Demo 1: hiding files into pictures using Winrar • Demo 2: using Stegosuite software to hide files inside images 

Audio Steganography • A weak tone is imperceptible in the presence of a strong tone in its temporal or spectral neighborhood. • The human ear cannot perceive frequencies at lower power level if these frequencies are present in the vicinity of tone-or noise-like frequencies at higher level. • Audio steganography consists of embedding a secret message into a digital audio signal. • The differences in the resulting audio file are not noticeable for the human ear. 

Audio Steganography • The dark knight rises movie in 2012 • On the website http://thedarkknightrises.com you find is a black screen with an audio file playing • Audio spectrum analysis of the audio file revealed a hashtag 

Audio Steganography • Demo 3: converting an image into sound wave • Demo 4: decoding a hidden sound inside a song • Demo 5: using Photoshop to hide text inside an audio file 

Video Steganography • Video = collection of images + sounds. • Same steganography techniques for images and audio. • Large amount of data can be hidden inside a video. • Hard to notice because of the continuous flow of information. 

Steganalysis • Steganography and Steganalysis are two different sides for the same coin. • Art of detecting Steganography. • Challenge: the suspected images, audio, or video may or may not have secret data. • Some of the techniques include: • Difference in file size between cover image and stego images • Increase or decrease of unique colors in stego images 

Steganography Thank you for your attention