SkyLen: a Skype-based length covert channel

Network covert channel is a technology that transfers information secretly through the computer network. The length-based covert channel is one of the most popular covert channels. Most of the existing length-based schemes are vulnerable to detections due to the abnormal statistical features of the covert traffic. In this paper, a Skype-based length covert channel SkyLen is proposed. The proposed method is based on the popular software Skype. The model of the Skype traffic is built first and then the encoding method is based on the built model. This will make the covert traffic has consistent high-order statistical feature with the normal case. Finally, for further improving the method’s stealth, the Monte Carlo sampling method is used in the encoding process. The capacity of the proposed method is 4bits/packet, and the detection experiments show that the proposed method is much stealthier than the existing one.