A Two-Way VoLTE Covert Channel with Feedback Adaptive to Mobile Network Environment

In the existing network covert channel research, the transmission of secret messages is one-way, lacking confirmation feedback on whether the secret message is successfully accepted. However, voice over LTE (VoLTE) has real-time interactive features, and the data packets between the sender and the receiver are transmitted in both directions, which facilitates the construction of a two-way covert channel with feedback. Therefore, we propose a two-way VoLTE covert channel adaptive to mobile network environment, which includes a sender-to-receiver covert timing channel that modulates covert message through actively dropping packets during the silence periods and a reverse covert storage channel that hides the acceptance of the covert message as feedback information into the feedback control information field of the real-time transport control protocol (RTCP) packet. The sender evaluates the current attack severity according to the feedback and adjusts the real-time parameters of the covert timing channel to weigh the robustness and other performance, thereby constructing a two-way covert channel adaptive to complex mobile network environments. Experimental results show that this solution can maintain voice quality which is an important performance indicator for VoLTE, while keeping the covert channel undetectable and robust.