A Covert Communication Model Based on Least Significant Bits Steganography in Voice over IP

Steganography, as one of alternative techniques for secure communications, has drawn more and more attentions. This paper presents a covert communication model based on least significant bits (LSB) steganography in Voice over IP (VoIP). The model aims at providing nice security of secret messages and real-time performance that is vital for VoIP. Therefore, we employ a simple encryption of secret messages before embedding them. This encryption strikes a good balance between adequate short-term protection for secret messages and low latency for VoIP. Furthermore, we design a structure of embedded messages. It can provide flexible length and avoid effectually both extraction attack and deceptive attack. We evaluate the model with ITU-T G.729a as the codec of the cover speech in StegTalk, our platform for study on covert communications theory in VoIP. In this case, the proposed model can provide two optional covert transmission speeds, i.e. 0.8 kb/s and 2.6 kb/s, where the maximum payload ratio is 99.98%. The experimental results show that our method has negligible effects on speech quality and well meets the real-time requirement of VoIP.