Title: DERMARK: A Dynamic, Efficient and Robust Multi-bit Watermark for Large Language Models
Primary area: alignment, fairness, safety, privacy, and societal considerations
Keywords: Multi-bit LLM Watermarking, LLM-generated Content Security, LLM Copyright Protection

Abstract: As large language models (LLMs) grow more powerful, concerns over copyright infringement of LLM-generated texts have intensified. LLM watermarking has been proposed to trace unauthorized redistribution or resale of generated content by embedding identifiers within the text. Existing approaches primarily rely on one-bit watermarking, which only verifies whether a text was generated by a specific LLM. In contrast, multi-bit watermarking encodes richer information, enabling identification of the specific LLM and user involved in generated or distributed content. However, current multi-bit methods directly embed the watermark without considering its capacity, which can result in failures, especially in low-entropy texts. In this paper, we analyze that the watermark embedding follows a normal distribution. We then derive a formal inequality to optimally segment the text for watermark embedding. Building upon this, we propose DERMARK, a dynamic, efficient, and robust multi-bit watermarking method that divides the text into variable-length segments for each watermark bit during inference. Moreover, DERMARK incurs negligible overhead since no additional intermediate matrices are generated and achieves robustness against text editing by minimizing watermark extraction loss. Experiments demonstrate that, compared to SOTA, on average, our method reduces the number of tokens required per embedded bit by 25\%, reduces watermark embedding time by 50\%, and maintains high robustness against text modifications and watermark erasure attacks.