By using non-normal channel to transfer the information, the covert channel brings great threats to network security on the one hand, but it provides an effective mechanism to transfer secret information and ensure information security on the other hand. In view of the present covert channel based on single protocol is easy to be detected by statistical rule, covert function not so good and unsuitable to transfer large amount of secret information, the hopping covert channel technique based on

more »

... ulti-protocol is presented in this paper. Firstly, the paper briefly introduces the covert channel technique and its current development, and then thoroughly analyzes the characteristics of each layer of the TCP/IP protocol; several implementation methods of covert channel based on single protocol are given. Finally, the design thought and key techniques of covert channel implementation based on protocol hopping are introduced in detail.