Merging-Resistant Watermarking for LoRA Modules

The widespread adoption of Low-Rank Adaptation (LoRA) modules in parameter-efficient fine-tuning has revolutionized the deployment of large-scale deep neural networks. However, the intellectual property protection of LoRA modules remains a critical challenge. White-box watermarking is a more effective solution than black-box watermarking in the multi-bit verification scenario of protecting and tracing intellectual property. However, existing white-box watermarking methods for LoRA lack both flexible multi-bit capacity and merging robustness, leaving LoRA modules vulnerable to unauthorized use and redistribution. In this paper, we propose a novel merging-resistant watermarking method for LoRA modules. Our method embeds watermarks into the increment matrix generated during LoRA merging and decomposes the watermark-induced modifications into LoRA's standard matrices, achieving reliable watermark extraction and preserving LoRA's efficiency. Specifically, we adopt quantization index modulation to embed watermarks in the low-frequency components of selected increment matrix weights. Extensive experiments demonstrate the effectiveness, imperceptibility, and robustness of our method, making it a practical solution for safeguarding LoRA modules in real-world applications. This work responds to the limited attention given to intellectual property protection for LoRA, contributing to the secure and sustainable development of deep learning technologies.