Steganography 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 => 1110100 1 Green : 205 => 1100110 1 Blue: 166 => 1010011 0 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 => 1001110 0 155 => 1001101 1 150 => 1001011 0 2 157 => 1001110 0 156 => 1001110 1 151 => 1001011 1 3 160 => 1010000 0 159 => 1001111 1 154 => 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.