Foreword 7
Acknowledgements 9
Contents 11
Chapter 1 Introduction 16
1.1 Steganography and Steganalysis as Empirical Sciences 16
1.2 Objective and Approach 17
1.3 Outline 19
Part I Background and Advances in Theory 23
Chapter 2 Principles of Modern Steganography and Steganalysis 24
2.1 Digital Steganography and Steganalysis 24
2.1.1 Steganographic System 25
2.1.2 Steganalysis 26
2.1.3 Relevance in Social and Academic Contexts 26
2.2 Conventions 27
2.3 Design Goals and Metrics 30
2.3.1 Capacity 30
2.3.2 Steganographic Security 31
2.3.3 Robustness 34
2.3.4 Further Metrics 35
2.4 Paradigms for the Design of Steganographic Systems 35
2.4.1 Paradigm I: Modify with Caution 35
2.4.2 Paradigm II: Cover Generation 36
2.4.3 Dominant Paradigm 38
2.5 Adversary Models 39
2.5.1 Passive Warden 39
2.5.2 Active Warden 41
2.6 Embedding Domains 43
2.6.1 Artificial Channels 43
2.6.2 Spatial and Time Domains 44
2.6.3 Transformed Domain 44
2.6.4 Selected Cover Formats: JPEG and MP3 48
2.6.4.1 Essentials of JPEG Still Image Compression 48
2.6.4.2 Essentials of MP3 Audio Compression 50
2.6.5 Exotic Covers 51
2.7 Embedding Operations 52
2.7.1 LSB Replacement 53
2.7.2 LSB Matching (卤1) 54
2.7.3 Mod-k Replacement, Mod-k Matching, and Generalisations 58
2.7.4 Multi-Sample Rules 60
2.7.5 Adaptive Embedding 61
2.8 Protocols and Message Coding 62
2.8.1 Public-Key Steganography 63
2.8.2 Maximising Embedding Efficiency 66
2.8.2.1 Embedding Efficiency with Respect to the Number of Changes 66
2.8.2.2 Embedding Efficiency with Respect to the Severity of Changes 68
2.8.2.3 Summary 70
2.9 Specific Detection Techniques 70
2.9.1 Calibration of JPEG Histograms 70
2.9.2 Universal Detectors 73
2.9.3 Quantitative Steganalysis 76
2.10 Selected Estimators for LSB Replacement in Spatial Domain Images 77
2.10.1 RS Analysis 77
2.10.2 Sample Pair Analysis 80
2.10.3 Higher-Order Structural Steganalysis 82
2.10.3.1 Least-Squares Solutions to SPA 83
2.10.3.2 Maximum-Likelihood Solutions to SPA 83
2.10.3.3 Triples and Quadruples Analysis 84
2.10.4 Weighted Stego Image Steganalysis 86
2.11 Summary and Further Steps 89
Chapter 3 Towards a Theory of Cover Models 91
3.1 Steganalyst's Problem Formalised 91
3.1.1 The Plausibility Heuristic 91
3.1.2 Application to Digital Steganography 93
3.1.3 Incognisability of the Cover Distribution 95
3.2 Cover Models 96
3.2.1 Defining Cover Models 96
3.2.2 Options for Formulating Cover Models 98
3.2.3 Cover Models and Detection Performance (by Example) 100
3.2.4 Summary and Motivations for Studying Cover Models 104
3.3 Dealing with Heterogeneous Cover Sources 105
3.3.1 Mixture Distributions 107
3.3.2 The Mixture Cover Model 107
3.4 Relation to Prior Information-Theoretic Work 109
3.4.1 Theoretical Limits 110
3.4.2 Observability Bounds 111
3.4.3 Computational Bounds 113
3.4.4 Applicability of the Theory of Cover Models 114
3.4.5 Indeterminacy in the Cover 116
3.5 Instances of Cover Models for Heterogeneous Sources 118
3.6 Summary 119
Part II Specific Advances in Steganalysis 121
Chapter 4 Detection of Model-Based Steganography with First-Order Statistics 122
4.1 Fundamentals of Model-Based Steganography 122
4.2 MB1: An Embedding Function for JPEG Covers 125
4.3 Detection Method 128
4.4 Experimental Validation 131
4.5 Summary and Outlook 134
4.5.1 Limitations and Future Directions for MB1Steganalysis 135
4.5.2 Possible (Short-Term) Countermeasures 136
4.5.3 Implications for More Secure Steganography 137
Chapter 5 Models of Heterogeneous Covers for Quantitative Steganalysis 138
5.1 Metrics for Quantitative Steganalysis 139
5.1.1 Conventional Metrics 139
5.1.2 Improved Metrics Based on a Distribution Model 141
5.1.3 Decomposition of Estimation Errors 146
5.1.3.1 Shape of the Error Distribution Components 147
5.1.3.2 Relative Size of Cover-Specific and Message-Specific Errors 150
5.2 Measurement of Sensitivity to Cover Properties 152
5.2.1 Method 153
5.2.2 Modelling the Shape of the Between-Image Distribution 155
5.2.3 Modelling the Shape of the Within-Image Distribution 159
5.3 Summary and Conclusion 162
6 Improved Weighted Stego Image Steganalysis 165
6.1 Enhanced WS for Never-Compressed Covers 165
6.1.1 Enhanced Predictor 166
6.1.2 Enhanced Calculation of Weights 171
6.1.3 Enhanced Bias Correction 176
6.1.4 Experimental Results 176
6.2 Adaptation of WS to JPEG Pre-Compressed Covers 182
6.2.1 Improved Predictor 183
6.2.2 Estimation of the Cover's JPEG Compression Quality 186
6.2.3 Experimental Results 187
6.3 Summary and Outlook 192
Chapter 7 Using Encoder Artefacts for Steganalysis of Compressed Audio Streams 193
7.1 MP3 Steganography and Steganalysis 193
7.1.1 Problem Statement in the Mixture Cover Model Framework 195
7.1.2 Level of Analysis and Related Work 195
7.1.3 Method 197
7.2 Description of Features 199
7.2.1 Features Based on the Compression Size Control Mechanism 200
7.2.2 Features Based on Model Decisions 202
7.2.3 Features Based on Capability Usage 204
7.2.4 Feature Based on Stream Formatting 205
7.3 Experimental Results for Encoder Detection 206
7.3.1 Single-Compressed Audio Files 206
7.3.2 Importance of Individual Features 209
7.3.3 Influence of Double-Compression 209
7.4 Experimental Results for Improved Steganalysis 211
7.5 Explorative Analysis of Encoder Similarities 212
7.6 Summary and Discussion 214
7.6.1 Limitations and Future Directions 214
7.6.2 Transferability to Other Formats 215
7.6.3 Related Applications 216
Part III Synthesis 217
Chapter 8 General Discussion 218
8.1 Summary of Results 218
8.1.1 Results Based on Informal Arguments 218
8.1.2 Results Based on Mathematical Proofs 219
8.1.3 Results Based on Empirical Evidence 220
8.2 Limitations 221
8.3 Directions for Future Research 222
8.3.1 Theoretical Challenges 223
8.3.2 Empirical Challenges 223
8.3.3 Practical Challenges 224
8.4 Conclusion and Outlook 224
Appendix A Description of Covers Used in the Experiments 227
Appendix B Spurious Steganalysis Results Using the `van Hateren' Image Database 230
Appendix C Proof of Weighted Stego Image (WS) Estimator 234
Appendix D Derivation of Linear Predictor for Enhanced WS 235
Appendix E Game for Formal Security Analysis 237
Appendix F Derivation of ROC Curves and AUC Metric for Example Cover Models 239
Appendix G Supplementary Figures and Tables 241
References 251
List of Tables 270
List of Figures 272
List of Acronyms 274
List of Symbols 277
List of Functions 282
Index 284