Security-Robustness Trade-offs in Diffusion Steganography: A Comparative Analysis of Pixel-Space and VAE-Based Architectures

Current generative steganography research mainly pursues computationally expensive mappings to perfect Gaussian priors within single diffusion model architectures. This work introduces an efficient framework based on approximate Gaussian mapping governed by a scale factor calibrated through capacity-aware adaptive optimization. Using this framework as a unified analytical tool, systematic comparative analysis of steganography in pixel-space models versus VAE-based latent-space systems is conducted. The investigation reveals a pronounced architecture dependent security-robustness trade-off: pixel-space models achieve high security against steganalysis but exhibit fragility to channel distortions, while VAE-based systems like Stable Diffusion offer substantial robustness at the cost of security vulnerabilities. Further analysis indicates that the VAE component drives this behavior through opposing mechanisms where the encoder confers robustness via manifold regularization while the decoder introduces vulnerabilities by amplifying latent perturbations into detectable artifacts. These findings characterize the conflicting architectural roles in generative steganography and establish a foundation for future research.