关键词: 隐蔽通道, 网络地址转换, 源端口号, 序列编码

Abstract: According to requirement of hiding the sending behavior and content in network transmission, this paper proposes a method using the transport layer source port to construct covert channel. This method sends the encoding information through these quential coding of UDP source port number. The covert channel can effectively apply to the NAT environment and construct a covert channel for transmitting the covert information from the inside local IP address to the outside global IP address. Through the experiments, the paper verifies the feasibility of this method and analyzes its data rate, stealthiness, and robustness. The covert channel can achieve 2 Kbit/s transmission speed when the network condition is nice.

Key words: covert channel, Network Address Translation（NAT）, source port, sequential coding