K-Space Bispectrum Steganography for Robust Unlearnable Data

The widespread availability of publicly accessible data on the internet accelerates the progress of deep learning but also raises concerns about unauthorized data usage for training neural networks. Early safeguard methods introduce small, carefully crafted perturbations via surrogate model into data to generate unlearnable data, aiming to prevent models from learning meaningful patterns. However, these methods lack robustness against adversarial training. Later, some works introduce adversarial examples to solve this problem but at the cost of increased overhead of the surrogate model. Recently, Convolution-based unlearnable data (CUDA), a surrogate-free method, has been proposed to address this issue by manually designed class-wise convolution kernels. Despite its success, CUDA suffers from high-frequency detail loss, perturbation hash collisions, and vulnerability to frequency filtering attacks. In this paper, we propose KBS (K-Space Bispectrum Steganography), which embeds class-specific information into the magnitude and phase components of the Fourier domain while preserving visual fidelity under reconstruction constraints. By directly performing steganography in the frequency domain, KBS preserves high-frequency details and avoids hash collisions with compact binary codes, enabling scalability to large-class datasets. Furthermore, KBS resists frequency filtering attacks by embedding perturbations in a way that remains imperceptible in the pixel space. Experimental results on public benchmarks demonstrate that KBS outperforms state-of-the-art methods.