Neural Linguistic Steganography with Controllable Security

Information hiding is an art and science with a long history and is widely used in covert communication. There are many ways to hide secret data in image, audio, and video. However, relatively few systems can hide information in text. Generative text steganography is a promising topic in natural language text infor-mation hiding. Previous generative text steganography methods use a fixed candidate pool generation rule, and they cannot effec-tively control the security of the generated text. The perceptual-imperceptibility and statistical-imperceptibility conflict effect also causes the poor quality of the steganographic text generated by previous generative text steganography methods. Moreover, pre-vious generative text steganography approaches barely discuss the robustness of steganographic text. This paper proposes a security controllable text steganography method that can generate natural-looking steganographic text with a statistical distribution that matches the natural language distribution. The proposed method combines the metrics of per-ceptual-imperceptibility and statistical-imperceptibility to calcu-late the combined distortion. It selects the tokens with the smallest combined distortion to construct a candidate pool at each time step. Moreover, the maximum combined distortion threshold is set when embedding secret messages to ensure controllable security. We conducted several experiments to evaluate the proposed model from the perspectives of embedding rate, perceptual-impercepti-bility, statistical-imperceptibility, and anti-attack ability. The ex-perimental results show that the proposed method can generate smooth and readable steganographic sentences with good re-sistance to steganalysis and high robustness.