Steganography via running short text messages

Abstract

Steganography, or covert communication between two parties through public channels, has been received a lot of attention, since the mere existence of encrypted message might cause suspicion and could even provide useful information to eavesdroppers. In some cases, secret information needs to be covertly broadcast to receivers in multiple locations at the same time. In this paper, we propose a novel steganographic scheme, which covertly sends secret message to multiple receivers via a stream of running short text messages displayed on a media output screen, assuming appropriate optical character recognition (OCR) functionality at the decoder. We use Thai language short text messages as a case study. We analyze the characteristics of Thai short text messages and introduce some effective message-to-bit transformation methods. We find that one Thai short text message can be transformed into multiple secret bits. In principle, the proposed transformation methods can be applied to short text messages in any language. We use a provably secure construction that guarantees covertness, privacy, and authenticity of the secret data against active attacks. In an experimental evaluation, we show that four secret message bits can be embedded in each short text message. In addition, we find that the embedded bits can be retrieved correctly and easily by human observers without OCR functionality at the decoder. Thus, the scheme is practical and effective for covert communication from one sender to multiple receivers over public channels.