  The purpose of the covert communication system is to implement the
communication process without causing third party perception. In order to
achieve complete covert communication, two aspects of security issues need to
be considered. The first one is to cover up the existence of information, that
is, to ensure the content security of information; the second one is to cover
up the behavior of transmitting information, that is, to ensure the behavioral
security of communication. However, most of the existing information hiding
models are based on the "Prisoners' Model", which only considers the content
security of carriers, while ignoring the behavioral security of the sender and
receiver. We think that this is incomplete for the security of covert
communication. In this paper, we propose a new covert communication framework,
which considers both content security and behavioral security in the process of
information transmission. In the experimental part, we analyzed a large amount
of collected real Twitter data to illustrate the security risks that may be
brought to covert communication if we only consider content security and
neglect behavioral security. Finally, we designed a toy experiment, pointing
out that in addition to most of the existing content steganography, under the
proposed new framework of covert communication, we can also use user's behavior
to implement behavioral steganography. We hope this new proposed framework will
help researchers to design better covert communication systems.
