Research On Covert Channel Based On Streaming Midea

Research on covert channel based on streaming media has been attracting more and more people’s attention. As a "multi-channel" carrier, streaming media is instantaneous and unpredictable. Using it to build covert channel for covert communication has incomparable advantages than others. So far, research on methods of building covert channel based on streaming media have had a number of research results. Compared with the forward studies, the study of reverse detection is still in its infancy, and has little effective detection algorithms. Most of the existing covert channels based on streaming media are limited to the compressed streaming of Internet VoIP such as G.711, G.723.1, G729a. But with the rapid development of3G mobile networks, research on mobile streaming based covert channel must be a trend in the future. In addition, system design and application of covert streaming channels are also far from enough.In view of the current research of covert channel based on streaming media, this article works in the four areas of reverse detection, building algorithms, system design and implementation, as well as application.In the reverse detection research, we design two efficient blind detection algorithm. The first detection method is based on Markov state transition, using Markov chain to model and analyse the parameters of streaming, and employing Markov state transition matrix as the classification feature vector. The second detection method is based on the rate of entropy. The method analyses the parameters of streaming media by using Markov source model. It employes the entropy rate of Markov source as the classification feature. Experimental results show that the two methods are superior to the existing algorithms in the aspects of detection accuracy and the size of detection window, and greatly improve the ability of detecting online.In the forward research, this paper proposes an adaptive covert channel scheme based on suboptimal coding. The method designs the steganographic embedding algorithm by making use of the redundancy of the fixed codebook search process, and introduces an adaptive parameter, to adjust the embedding rate during the switch of coding bit rate, for always keeping good speech qualities. The bandwidth of the covert channel built by the method is up to3.2kbps. Experiments show that the steganography based on suboptimal coding, brings no additional computational complexity to the encoder, and has good imperceptibility (in term of high speech quality) and strong anti-detection property. The existing detection algorithms are useless for the method. In addition, the paper also presents a high rate covert channel based on rate camouflage. It fills the covert messages into the tail of the speech frame of a low bit rate coder, disguised as a speech frame of a high rate coder, and uses SRTP protocol to encrypt the frame for safety. The bandwidth of the covert channel built by the method is up to5.6kbps. Experiments show that the method has the strong usability in terms of hidden capacity and safety.In the system design and implementation research, based on the positive results of the forward research, the paper design and implement a covert channel system on3G phone-Stegdroid. The system introduces semi-reliable transmission control mechanism and supports any form of data transmission. Stegdroid can build single and duplex covert channels, with a bandwidth among3.2kbps～5.6kbps. Test results show Stegdroid is stable, and can be used in3G,4G and wifi networks, which has a strong usability.In application research, we propose to use covert channel to save transmission bandwidth of streaming media. Taking the AMR-WB for example, the paper details the basic principles and workflow of using covert channel to reduce the transmission bandwidth of streaming media. The experimental results show that this method can contribute to10.7%～15.1%(1.6kbps～2.55kbps) bandwidth reduction for AMR-WB, with little degradation of the speech quality. This method can effectively save network bandwidth resources, reducing the load of streaming media network. Although the method is only applied to AMR-WB as an example in this article, the idea can be be further applied in any other streaming media and the basic principle is the same.