Abstract: A covert channel represents an unforeseen method of communication that utilizes authorized public communication as a carrier medium for covert messages.A covert channel can be a safe and efficient way to transmit confidential information hidden in explicit traffic.Existing streaming-based covert channels are often easily detected due to the establishment of new communication links.For this reason,this paper conducted targeted tests and research on data pa-ckets passing through the streaming media server.It is found that the existing closed source streaming media does not strictly check the data packets passing through the server,and the data packets can still reach the termina lafter modi-fying some data.Based on the above facts,this paper established a hidden channel based on closed source streaming media by exploring the data bit distribution rules of the modified data packets through the server.In order to improve the entropy value of the data packet,this paper used an efficient and compact speck algorithm to encrypt the packet content.In order to monitor existing links and real-time traffic in real time,the firewalls were connected in series in the network structure,and the network connection and communication quality were monitored by a firewall.Experimental data show that this method does not increase the number of network connections and does not affect the communication qua-lity,and it is compatible with a variety of streaming media devices,showing that this method is practical and not easily detected.Moreover,since the hidden channel is mounted on the closed source streaming medium,the transmission efficiency of the covert information is high.The above results show that the method of establishing a covert channel based on the communication flow of the existing closed source streaming media software is feasible,and has strong concealment after encrypting the content of the data packet.

Key words: Covert channels, Instant messaging, Multimedia stream, Traffic analysis, VoIP