Advanced Statistical Steganalysis (eBook)

Foreword 
8 
Acknowledgements 
10 
Contents 
12 
Chapter 1 Introduction 17
1.1 Steganography and Steganalysis as Empirical Sciences 17
1.2 Objective and Approach 18
1.3 Outline 20
Part I Background and Advances in Theory 24
Chapter 2 Principles of Modern Steganography and Steganalysis 25
2.1 Digital Steganography and Steganalysis 25
2.1.1 Steganographic System 26
2.1.2 Steganalysis 27
2.1.3 Relevance in Social and Academic Contexts 27
2.2 Conventions 28
2.3 Design Goals and Metrics 31
2.3.1 Capacity 31
2.3.2 Steganographic Security 32
2.3.3 Robustness 35
2.3.4 Further Metrics 36
2.4 Paradigms for the Design of Steganographic Systems 36
2.4.1 Paradigm I: Modify with Caution 36
2.4.2 Paradigm II: Cover Generation 37
2.4.3 Dominant Paradigm 39
2.5 Adversary Models 40
2.5.1 Passive Warden 40
2.5.2 Active Warden 42
2.6 Embedding Domains 44
2.6.1 Artificial Channels 44
2.6.2 Spatial and Time Domains 45
2.6.3 Transformed Domain 45
2.6.4 Selected Cover Formats: JPEG and MP3 49
2.6.4.1 Essentials of JPEG Still Image Compression 49
2.6.4.2 Essentials of MP3 Audio Compression 51
2.6.5 Exotic Covers 52
2.7 Embedding Operations 53
2.7.1 LSB Replacement 54
2.7.2 LSB Matching (±1) 55
2.7.3 Mod-k Replacement, Mod-k Matching, and Generalisations 59
2.7.4 Multi-Sample Rules 61
2.7.5 Adaptive Embedding 62
2.8 Protocols and Message Coding 63
2.8.1 Public-Key Steganography 64
2.8.2 Maximising Embedding Efficiency 67
2.8.2.1 Embedding Efficiency with Respect to the Number of Changes 67
2.8.2.2 Embedding Efficiency with Respect to the Severity of Changes 69
2.8.2.3 Summary 71
2.9 Specific Detection Techniques 71
2.9.1 Calibration of JPEG Histograms 71
2.9.2 Universal Detectors 74
2.9.3 Quantitative Steganalysis 77
2.10 Selected Estimators for LSB Replacement in Spatial Domain Images 78
2.10.1 RS Analysis 78
2.10.2 Sample Pair Analysis 81
2.10.3 Higher-Order Structural Steganalysis 83
2.10.3.1 Least-Squares Solutions to SPA 84
2.10.3.2 Maximum-Likelihood Solutions to SPA 84
2.10.3.3 Triples and Quadruples Analysis 85
2.10.4 Weighted Stego Image Steganalysis 87
2.11 Summary and Further Steps 90
Chapter 3 Towards a Theory of Cover Models 92
3.1 Steganalyst's Problem Formalised 92
3.1.1 The Plausibility Heuristic 92
3.1.2 Application to Digital Steganography 94
3.1.3 Incognisability of the Cover Distribution 96
3.2 Cover Models 97
3.2.1 Defining Cover Models 97
3.2.2 Options for Formulating Cover Models 99
3.2.3 Cover Models and Detection Performance (by Example) 
101 
3.2.4 Summary and Motivations for Studying Cover Models 105
3.3 Dealing with Heterogeneous Cover Sources 106
3.3.1 Mixture Distributions 108
3.3.2 The Mixture Cover Model 108
3.4 Relation to Prior Information-Theoretic Work 110
3.4.1 Theoretical Limits 111
3.4.2 Observability Bounds 112
3.4.3 Computational Bounds 114
3.4.4 Applicability of the Theory of Cover Models 115
3.4.5 Indeterminacy in the Cover 117
3.5 Instances of Cover Models for Heterogeneous Sources 119
3.6 Summary 120
Part II Specific Advances in Steganalysis 122
Chapter 4 Detection of Model-Based Steganography with First-Order Statistics 123
4.1 Fundamentals of Model-Based Steganography 123
4.2 MB1: An Embedding Function for JPEG Covers 126
4.3 Detection Method 129
4.4 Experimental Validation 132
4.5 Summary and Outlook 135
4.5.1 Limitations and Future Directions for MB1Steganalysis 136
4.5.2 Possible (Short-Term) Countermeasures 137
4.5.3 Implications for More Secure Steganography 138
Chapter 5 Models of Heterogeneous Covers for Quantitative Steganalysis 139
5.1 Metrics for Quantitative Steganalysis 140
5.1.1 Conventional Metrics 140
5.1.2 Improved Metrics Based on a Distribution Model 142
5.1.3 Decomposition of Estimation Errors 147
5.1.3.1 Shape of the Error Distribution Components 148
5.1.3.2 Relative Size of Cover-Specific and Message-Specific Errors 151
5.2 Measurement of Sensitivity to Cover Properties 153
5.2.1 Method 154
5.2.2 Modelling the Shape of the Between-Image Distribution 156
5.2.3 Modelling the Shape of the Within-Image Distribution 160
5.3 Summary and Conclusion 163
6 Improved Weighted Stego Image Steganalysis 166
6.1 Enhanced WS for Never-Compressed Covers 166
6.1.1 Enhanced Predictor 167
6.1.2 Enhanced Calculation of Weights 172
6.1.3 Enhanced Bias Correction 177
6.1.4 Experimental Results 177
6.2 Adaptation of WS to JPEG Pre-Compressed Covers 183
6.2.1 Improved Predictor 184
6.2.2 Estimation of the Cover's JPEG Compression Quality 187
6.2.3 Experimental Results 188
6.3 Summary and Outlook 193
Chapter 7 Using Encoder Artefacts for Steganalysis of Compressed Audio Streams 194
7.1 MP3 Steganography and Steganalysis 194
7.1.1 Problem Statement in the Mixture Cover Model Framework 196
7.1.2 Level of Analysis and Related Work 196
7.1.3 Method 198
7.2 Description of Features 200
7.2.1 Features Based on the Compression Size Control Mechanism 201
7.2.2 Features Based on Model Decisions 203
7.2.3 Features Based on Capability Usage 205
7.2.4 Feature Based on Stream Formatting 206
7.3 Experimental Results for Encoder Detection 207
7.3.1 Single-Compressed Audio Files 207
7.3.2 Importance of Individual Features 210
7.3.3 Influence of Double-Compression 210
7.4 Experimental Results for Improved Steganalysis 212
7.5 Explorative Analysis of Encoder Similarities 213
7.6 Summary and Discussion 215
7.6.1 Limitations and Future Directions 215
7.6.2 Transferability to Other Formats 216
7.6.3 Related Applications 217
Part III Synthesis 218
Chapter 8 General Discussion 219
8.1 Summary of Results 219
8.1.1 Results Based on Informal Arguments 219
8.1.2 Results Based on Mathematical Proofs 220
8.1.3 Results Based on Empirical Evidence 221
8.2 Limitations 222
8.3 Directions for Future Research 223
8.3.1 Theoretical Challenges 224
8.3.2 Empirical Challenges 224
8.3.3 Practical Challenges 225
8.4 Conclusion and Outlook 225
Appendix A Description of Covers Used in the Experiments 228
Appendix B Spurious Steganalysis Results Using the `van Hateren' Image Database 231
Appendix C Proof of Weighted Stego Image (WS) Estimator 235
Appendix D Derivation of Linear Predictor for Enhanced WS 236
Appendix E Game for Formal Security Analysis 238
Appendix F Derivation of ROC Curves and AUC Metric for Example Cover Models 240
Appendix G Supplementary Figures and Tables 242
References 252
List of Tables 271
List of Figures 273
List of Acronyms 275
List of Symbols 278
List of Functions 283
Index 285