Secure Steganographic Cover Generation via a Noise-Optimization Stacked StyleGAN2.

Recently, the style-based generative adversarial network StyleGAN2 yields state-of-art performance on unconditional high-quality image synthesis. However, from the perspective of steganography, the image security is not guaranteed during the image synthesis. Relying on the optimal properties of StyleGAN2, this paper proposes a noise-optimization stacked StyleGAN2 named NOStyle to generate the secure and high-quality cover (image used for data hiding). In our proposed scheme, we decompose the image synthesis into two stages with symmetrical mode. In stage-I, StyleGAN2 is preserved to generate a high-quality benchmark image. In the stage-II generator, based on the progressive mechanism and shortcut connection, we design a noise secure optimization network by which the different-scale stochastic variation (noise map) is automatically adjusted according to the results of the stage-II discriminator. After injecting the stochastic variation into different resolutions of the synthesis network, the stage-II generator obtains an intermediate image. For the symmetrical stage-II discriminator, we combine the image secure loss and fidelity loss to construct the noise loss which is used to evaluate the difference between two images generated by the stage-I generator and stage-II generator. Taking the outputs of stage-II discriminator as inputs, by iteration, the stage-II generator finally creates the optimal image. Extensive experiments show that the generated image is not only secure but high quality. Moreover, we make a conclusion that the security of the generated image is inverse proportion to the fidelity.