OSNIP: Breaking the Privacy-Utility-Efficiency Trilemma in LLM Inference via Obfuscated Semantic Null Space
Zhiyuan Cao, Zeyu Ma, Chenhao Yang, HAN ZHENG, Mingang Chen
Abstract
We propose Obfuscated Semantic Null space Injection for Privacy (OSNIP), a lightweight client-side encryption framework for privacy-preserving LLM inference. Generalizing the geometric intuition of linear kernels to the high-dimensional latent space of LLMs, we formally define the ``Obfuscated Semantic Null Space'', a high-dimensional regime that preserves semantic fidelity while enforcing near-orthogonality to the original embedding. By injecting perturbations that project the original embedding into this space, OSNIP ensures privacy without any post-processing. Furthermore, OSNIP employs a key-dependent stochastic mapping that synthesizes individualized perturbation trajectories unique to each user. Evaluations on 12 generative and classification benchmarks show that OSNIP achieves state-of-the-art performance, sharply reducing attack success rates while maintaining strong model utility under strict security constraints.
BibTeX
@inproceedings{
cao2026osnip,
title={{OSNIP}: Balancing the Privacy-Utility-Efficiency Trilemma in {LLM} Inference via Obfuscated Semantic Null Space},
author={Zhiyuan Cao and Zeyu Ma and Chenhao Yang and HAN ZHENG and Mingang Chen},
booktitle={Forty-third International Conference on Machine Learning},
year={2026},
url={https://openreview.net/forum?id=YsexiJ0zAh}
}