Building covert channels over the packet reordering phenomenon

New modes of communication have shown themselves to be needed for more secure and private types of data. Steganography or data-hiding through covert channels can be highly motivated by today's security requirements and various needs of applications. Moreover, the amount of information in the Internet traffic is not bounded by what is contained in packets payload; there is considerable hidden capacity within packets and flows characteristics to build robust and stealthy covert channels. In this paper, we propose using the packet reordering phenomenon as the media to carry a hidden channel. As a naturally occurring behavior of packets traveling the Internet, it can as well be induced to send a signal to the receiving end. Specific permutations are selected to enhance the reliability of the channel, while their distribution was selected to imitate real traffic and increase stealthiness. The robustness of such channel is analyzed, and its bandwidth is calculated. A simple tool is implemented to communicate over the natural phenomenon of packet reordering. Reliability and capacity of the techniques are evaluated and promising results show the potential of the proposed approach.