Building packet length covert channel over mobile VoIP traffics

In this paper, we propose constructing covert channel via partitioning the length distribution of legitimate packet traffics and mapping packet length partitions to data symbols. The reliable data transmission of covert channel is guaranteed by precoding the hidden data into a HDLC-like frame structure and the channel performance can be raised by selective parameter settings. A testbed is setup to simulate covert communication over the natural mobile VoIP traffics. Undetectability, reliability and throughput of the scheme are evaluated and experiment results show the potential of the proposed approach. Moreover, the proposed scheme can also be applied to other communication scenarios without or with little modifications.