Practical Insecurity for Effective Steganalysis
Information Hiding
On steganographic chosen covertext security
ICALP'05 Proceedings of the 32nd international conference on Automata, Languages and Programming
Upper and lower bounds on black-box steganography
TCC'05 Proceedings of the Second international conference on Theory of Cryptography
Provably secure steganography with imperfect sampling
PKC'06 Proceedings of the 9th international conference on Theory and Practice of Public-Key Cryptography
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Informally, steganography refers to the practice of hiding secret messages in communications over a public channel so that an eavesdropper (who listens to all communications) cannot even tell that a secret message is being sent. In contrast to the active literature proposing new concrete steganographic protocols and analysing flaws in existing protocols, there has been very little work on formalizing steganographic notions of security, and none giving complete, rigorous proofs of security in a satisfying model. My thesis initiates the study of steganography from a cryptographic point of view. We give a precise model of a communication channel and a rigorous definition of steganographic security, and prove that relative to a channel oracle, secure steganography exists if and only if one-way functions exist. We give tightly matching upper and lower bounds on the maximum rate of any secure stegosystem. We introduce the concept of steganographic key exchange and public-key steganography, and show that provably secure protocols for these objectives exist under a variety of standard number-theoretic assumptions. We consider several notions of active attacks against steganography, show how to achieve each under standard assumptions, and consider the relationships between these notions. Finally, we extend the concept of steganography as covert communication to include the more general concept of covert computation.