A hybrid covert channel with feedback over mobile networks

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, 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 hybrid covert channel over mobile networks, 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 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. Experimental results show that this solution can effectively feedback the transmission of the covert message while keeping undetectable and robust.