1. Steganography University of Palestine Eng. Wisam Zaqoot April 2011 ITSS 4201 Internet Insurance and Information Hiding

2. The prisoners problem Alice and Bob are in jail and wish to hatch an escape plan. Alice and Bob are in jail and wish to hatch an escape plan. Alice's and Bob's communication pass through Willy. Alice's and Bob's communication pass through Willy. Alice's and Bob's goal is to hide their ciphertext in innocuous looking way so that Willy will not become suspicious. Alice's and Bob's goal is to hide their ciphertext in innocuous looking way so that Willy will not become suspicious. If Willy is a passive warden he will not do any thing to Alice's and Bob's communication. If Willy is a passive warden he will not do any thing to Alice's and Bob's communication. If Willy is an active warden he will alter the data being sent between Alice and Bob. If Willy is an active warden he will alter the data being sent between Alice and Bob.

3. Problem Formulation Hello “Hello” Willy

4. The concept Yes No Embedding Algorithm Cover Message Stego Message Secret Key Secret Message Message Retrieval Algorithm Secret Message Secret Key Is Stego Message? Suppress Message AliceWillyBob

5. Stego-system Criteria Cover data should not be significantly modified in order not to make it perceptible to human perception system Cover data should not be significantly modified in order not to make it perceptible to human perception system The embedded data should be directly encoded in the cover & not in wrapper or header The embedded data should be directly encoded in the cover & not in wrapper or header Embedded data should be immune to modifications to cover Embedded data should be immune to modifications to cover

6. Places to Hide Information: Steganography Images Images Audio files Audio files Text Text Video Video We focus on Images as cover media. Though most ideas apply to video and audio as well. We focus on Images as cover media. Though most ideas apply to video and audio as well. But first, we will begin by studying steganography in text and audio.

7. Steganography in Text Soft Copy Text Soft Copy Text Encode data by varying the number of spaces after punctuationEncode data by varying the number of spaces after punctuation Slight modifications of formatted text will be immediately apparent to anyone reading the textSlight modifications of formatted text will be immediately apparent to anyone reading the text Use of White Space (tabs & spaces) is more effective and less noticeableUse of White Space (tabs & spaces) is more effective and less noticeable This is most common method for hiding data in textThis is most common method for hiding data in text

8. Steganography in Text Soft Copy Text Soft Copy Text Encode data in additional spaces placed at the end of a lineEncode data in additional spaces placed at the end of a line Four score and seven years ago our forefathers

9. Steganography in Text Hard Copy Text Hard Copy Text Line Shift CodingLine Shift Coding Shifts every other line up or down slightly in order to encode data Shifts every other line up or down slightly in order to encode data Word Shift CodingWord Shift Coding Shifts some words slightly left or right in order to encode data Shifts some words slightly left or right in order to encode data

10. Steganography in Audio Low Bit Coding Low Bit Coding Phase Coding Phase Coding Spread Spectrum Spread Spectrum Echo Data Hiding Echo Data Hiding

11. Steganography in Audio Low Bit Coding Low Bit Coding Most digital audio is created by sampling the signal and quantizing the sample with a 16-bit quantizer.Most digital audio is created by sampling the signal and quantizing the sample with a 16-bit quantizer. The rightmost bit, or low order bit, of each sample can be changed from 0 to 1 or 1 to 0The rightmost bit, or low order bit, of each sample can be changed from 0 to 1 or 1 to 0 This modification from one sample value to another is not perceptible by most people and the audio signal still sounds the sameThis modification from one sample value to another is not perceptible by most people and the audio signal still sounds the same

12. Steganography in Audio Phase Coding Phase Coding Relies on the relative insensitivity of the human auditory system to phase changesRelies on the relative insensitivity of the human auditory system to phase changes Substitutes the initial phase of an audio signal with a reference phase that represents the dataSubstitutes the initial phase of an audio signal with a reference phase that represents the data More complex than low bit encoding, but it is much more robust and less likely to distort the signal that is carrying the hidden data.More complex than low bit encoding, but it is much more robust and less likely to distort the signal that is carrying the hidden data.

13. Steganography in Audio Direct Sequence Spread Spectrum Direct Sequence Spread Spectrum Spreads the signal by multiplying it by a chip, which is a maximal length pseudorandom sequenceSpreads the signal by multiplying it by a chip, which is a maximal length pseudorandom sequence DSSS introduces additive random noise to the sound fileDSSS introduces additive random noise to the sound file

14. Steganography in Audio Echo Data Hiding Echo Data Hiding Discrete copies of the original signal are mixed in with the original signal creating echoes of each sound.Discrete copies of the original signal are mixed in with the original signal creating echoes of each sound. By using two different time values between an echo and the original sound, a binary 1 or binary 0 can be encoded.By using two different time values between an echo and the original sound, a binary 1 or binary 0 can be encoded. Also, initial amplitudeAlso, initial amplitude and decay rate can and decay rate can be set below the audible threshold of the human ear.

15. Why MP3 Files? Open Standard (as opposed to proprietary WMA) Open Standard (as opposed to proprietary WMA) Very Popular Very Popular Preferred by end users Preferred by end users Easily Available Easily Available

16. MP3 Stegonography Principle : Audio signals contain a significant portion of information that can be discarded without average listener noticing the change. Principle : Audio signals contain a significant portion of information that can be discarded without average listener noticing the change. MP3Stego – tool developed by Fabien A.P. Petitcolas MP3Stego – tool developed by Fabien A.P. Petitcolas Tool operates within MP3 encoding process Tool operates within MP3 encoding process The data to be hidden is first compressed, encrypted and hidden in MP3 bit stream. The data to be hidden is first compressed, encrypted and hidden in MP3 bit stream. Quantization of original audio signal takes place. Quantization of original audio signal takes place. At the same time, for some selected points, data is introduced in the quantized output, At the same time, for some selected points, data is introduced in the quantized output, Distortions introduced by these are constantly checked for to satisfy the psychoacoustics model. Distortions introduced by these are constantly checked for to satisfy the psychoacoustics model. A variable records the number of bits that are for data in the actual audio, data for huffman coding and hidden data. A variable records the number of bits that are for data in the actual audio, data for huffman coding and hidden data. Key is selected using pseudo random bit generator based on SHA-1 and dictates the values that would be modified to hold the hidden data. Key is selected using pseudo random bit generator based on SHA-1 and dictates the values that would be modified to hold the hidden data.

17. Why Post Encode Stego? Easy to implement Easy to implement Do not require source WAV files Do not require source WAV files Can be used with an of the shelf encoder Can be used with an of the shelf encoder No sound quality degradation No sound quality degradation