Public-key steganography

Informally, a public-key steganography protocol allows two parties, who have never met or exchanged a secret, to send hidden messages over a public channel so that an adversary cannot even detect that these hidden messages are being sent. Unlike previous settings in which provable security has been applied to steganography, public-key steganography is information-theoretically impossible. In this work we introduce computational security conditions for public-key steganography similar to those introduced by Hopper, Langford and von Ahn [7] for the private-key setting. We also give the first protocols for publickey steganography and steganographic key exchange that are provably secure under standard cryptographic assumptions. Additionally, in the random oracle model, we present a protocol that is secure against adversaries that have access to a decoding oracle (a steganographic analogue of Rackoff and Simon's attacker-specific adaptive chosen-ciphertext adversaries from CRYPTO 91 [10]).