## Cryptology ePrint Archive: Report 2013/078

Nelly Fazio and Antonio R. Nicolosi and Irippuge Milinda Perera

Abstract: We initiate the study of broadcast steganography (BS), an extension of steganography to the multi-recipient setting. BS enables a sender to communicate covertly with a dynamically designated set of receivers, so that the recipients recover the original content, while unauthorized users and outsiders remain \emph{unaware} of the covert communication. One of our main technical contributions is the introduction of a new variant of anonymous broadcast encryption that we term \emph{outsider-anonymous broadcast encryption with pseudorandom ciphertexts} (oABE$). Our oABE$ construction achieves sublinear ciphertext size and is secure in the standard model. Besides being of interest in its own right, oABE\$ enables an efficient construction of BS secure in the standard model against adaptive adversaries with sublinear communication complexity.