Advanced Statistical Steganalysis

Foreword

Acknowledgements

Contents

Chapter 1 Introduction

1.1 Steganography and Steganalysis as Empirical Sciences

1.2 Objective and Approach

1.3 Outline

Part I Background and Advances in Theory

Chapter 2 Principles of Modern Steganography and Steganalysis

2.1 Digital Steganography and Steganalysis

2.1.1 Steganographic System

2.1.2 Steganalysis

2.1.3 Relevance in Social and Academic Contexts

2.2 Conventions

2.3 Design Goals and Metrics

2.3.1 Capacity

2.3.2 Steganographic Security

2.3.3 Robustness

2.3.4 Further Metrics

2.4 Paradigms for the Design of Steganographic Systems

2.4.1 Paradigm I: Modify with Caution

2.4.2 Paradigm II: Cover Generation

2.4.3 Dominant Paradigm

2.5 Adversary Models

2.5.1 Passive Warden

2.5.2 Active Warden

2.6 Embedding Domains

2.6.1 Artificial Channels

2.6.2 Spatial and Time Domains

2.6.3 Transformed Domain

2.6.4 Selected Cover Formats: JPEG and MP3

2.6.4.1 Essentials of JPEG Still Image Compression

2.6.4.2 Essentials of MP3 Audio Compression

2.6.5 Exotic Covers

2.7 Embedding Operations

2.7.1 LSB Replacement

2.7.2 LSB Matching (±1)

2.7.3 Mod-k Replacement, Mod-k Matching, and Generalisations

2.7.4 Multi-Sample Rules

2.7.5 Adaptive Embedding

2.8 Protocols and Message Coding

2.8.1 Public-Key Steganography

2.8.2 Maximising Embedding Efficiency

2.8.2.1 Embedding Efficiency with Respect to the Number of Changes

2.8.2.2 Embedding Efficiency with Respect to the Severity of Changes

2.8.2.3 Summary

2.9 Specific Detection Techniques

2.9.1 Calibration of JPEG Histograms

2.9.2 Universal Detectors

2.9.3 Quantitative Steganalysis

2.10 Selected Estimators for LSB Replacement in Spatial Domain Images

2.10.1 RS Analysis

2.10.2 Sample Pair Analysis

2.10.3 Higher-Order Structural Steganalysis

2.10.3.1 Least-Squares Solutions to SPA

2.10.3.2 Maximum-Likelihood Solutions to SPA

2.10.3.3 Triples and Quadruples Analysis

2.10.4 Weighted Stego Image Steganalysis

2.11 Summary and Further Steps

Chapter 3 Towards a Theory of Cover Models

3.1 Steganalyst's Problem Formalised

3.1.1 The Plausibility Heuristic

3.1.2 Application to Digital Steganography

3.1.3 Incognisability of the Cover Distribution

3.2 Cover Models

3.2.1 Defining Cover Models

3.2.2 Options for Formulating Cover Models

3.2.3 Cover Models and Detection Performance (by Example)

3.2.4 Summary and Motivations for Studying Cover Models

3.3 Dealing with Heterogeneous Cover Sources

3.3.1 Mixture Distributions

3.3.2 The Mixture Cover Model

3.4 Relation to Prior Information-Theoretic Work

3.4.1 Theoretical Limits

3.4.2 Observability Bounds

3.4.3 Computational Bounds

3.4.4 Applicability of the Theory of Cover Models

3.4.5 Indeterminacy in the Cover

3.5 Instances of Cover Models for Heterogeneous Sources

3.6 Summary

Part II Specific Advances in Steganalysis

Chapter 4 Detection of Model-Based Steganography with First-Order Statistics

4.1 Fundamentals of Model-Based Steganography

4.2 MB1: An Embedding Function for JPEG Covers

4.3 Detection Method

4.4 Experimental Validation

4.5 Summary and Outlook

4.5.1 Limitations and Future Directions for MB1Steganalysis

4.5.2 Possible (Short-Term) Countermeasures

4.5.3 Implications for More Secure Steganography

Chapter 5 Models of Heterogeneous Covers for Quantitative Steganalysis

5.1 Metrics for Quantitative Steganalysis

5.1.1 Conventional Metrics

5.1.2 Improved Metrics Based on a Distribution Model

5.1.3 Decomposition of Estimation Errors

5.1.3.1 Shape of the Error Distribution Components

5.1.3.2 Relative Size of Cover-Specific and Message-Specific Errors

5.2 Measurement of Sensitivity to Cover Properties

5.2.1 Method

5.2.2 Modelling the Shape of the Between-Image Distribution

5.2.3 Modelling the Shape of the Within-Image Distribution

5.3 Summary and Conclusion

6 Improved Weighted Stego Image Steganalysis

6.1 Enhanced WS for Never-Compressed Covers

6.1.1 Enhanced Predictor

6.1.2 Enhanced Calculation of Weights

6.1.3 Enhanced Bias Correction

6.1.4 Experimental Results

6.2 Adaptation of WS to JPEG Pre-Compressed Covers

6.2.1 Improved Predictor

6.2.2 Estimation of the Cover's JPEG Compression Quality

6.2.3 Experimental Results

6.3 Summary and Outlook

Chapter 7 Using Encoder Artefacts for Steganalysis of Compressed Audio Streams

7.1 MP3 Steganography and Steganalysis

7.1.1 Problem Statement in the Mixture Cover Model Framework

7.1.2 Level of Analysis and Related Work

7.1.3 Method

7.2 Description of Features

7.2.1 Features Based on the Compression Size Control Mechanism

7.2.2 Features Based on Model Decisions

7.2.3 Features Based on Capability Usage

7.2.4 Feature Based on Stream Formatting

7.3 Experimental Results for Encoder Detection

7.3.1 Single-Compressed Audio Files

7.3.2 Importance of Individual Features

7.3.3 Influence of Double-Compression

7.4 Experimental Results for Improved Steganalysis

7.5 Explorative Analysis of Encoder Similarities

7.6 Summary and Discussion

7.6.1 Limitations and Future Directions

7.6.2 Transferability to Other Formats

7.6.3 Related Applications

Part III Synthesis

Chapter 8 General Discussion

8.1 Summary of Results

8.1.1 Results Based on Informal Arguments

8.1.2 Results Based on Mathematical Proofs

8.1.3 Results Based on Empirical Evidence

8.2 Limitations

8.3 Directions for Future Research

8.3.1 Theoretical Challenges

8.3.2 Empirical Challenges

8.3.3 Practical Challenges

8.4 Conclusion and Outlook

Appendix A Description of Covers Used in the Experiments

Appendix B Spurious Steganalysis Results Using the `van Hateren' Image Database

Appendix C Proof of Weighted Stego Image (WS) Estimator

Appendix D Derivation of Linear Predictor for Enhanced WS

Appendix E Game for Formal Security Analysis

Appendix F Derivation of ROC Curves and AUC Metric for Example Cover Models

Appendix G Supplementary Figures and Tables

References

List of Tables

List of Figures

List of Acronyms

List of Symbols

List of Functions

Index