  Steganography is a technique for covert communication between two parties.
With the rapid development of deep neural networks (DNN), more and more
steganographic networks are proposed recently, which are shown to be promising
to achieve good performance. Unlike the traditional handcrafted steganographic
tools, a steganographic network is relatively large in size. It raises concerns
on how to covertly transmit the steganographic network in public channels,
which is a crucial stage in the pipeline of steganography in real world
applications. To address such an issue, we propose a novel scheme for
steganography of steganographic networks in this paper. Unlike the existing
steganographic schemes which focus on the subtle modification of the cover data
to accommodate the secrets. We propose to disguise a steganographic network
(termed as the secret DNN model) into a stego DNN model which performs an
ordinary machine learning task (termed as the stego task). During the model
disguising, we select and tune a subset of filters in the secret DNN model to
preserve its function on the secret task, where the remaining filters are
reactivated according to a partial optimization strategy to disguise the whole
secret DNN model into a stego DNN model. The secret DNN model can be recovered
from the stego DNN model when needed. Various experiments have been conducted
to demonstrate the advantage of our proposed method for covert communication of
steganographic networks as well as general DNN models.
