Improving performance of network covert timing channel through Huffman coding

Network covert channel is a mechanism used to transfer covert message violating security policies through network. Performance of a channel is crucial to an attacker. Some studies have improved the performance by advancing the coding mechanism, but few ones have taken account of the redundancy of covert message. This paper introduces Huffman coding scheme to compress the transferred data by exploiting redundancy, and investigates the performance of the network timing channel according to the channel capacity and covertness. A mathematical model of capacity is presented and the effects of the parameters are analyzed. The experiment examines how the network delays and the Huffman coding scheme affect the capacity and covertness, and the results demonstrate that the performance of the timing channel is improved.