Robust Text Watermarking for Large Language Models via Dual Semantic Embeddings

Jonas Schäfer, Cezary Pilaszewicz, Gerhard Wunder


Abstract
This work presents Dual-Embedding Watermarking (DEW), a semantic watermarking scheme for large language models (LLMs) that leverages contextual and token-level embeddings to enhance robustness against paraphrasing and translation. DEW utilizes a signal-processing methodology, applying algebraic vector-space operations to token and context embeddings to derive a watermark signal that degrades gracefully under semantic shifts. The method obfuscates the watermark by projecting embedding vectors through pseudo-random matrices seeded with a secret key. Experimental results show that dual-embedding watermarking can offer state-of-the-art robustness, particularly against translation, while incurring relatively low computational overhead compared with other semantic schemes. At lower watermark strength, DEW also maintains competitive text quality, suggesting that dual-embedding signals provide a promising substrate for robust semantic watermarking.
Anthology ID:
2026.findings-emnlp.959
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
20266–20287
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.959/
DOI:
10.18653/2026.findings-emnlp.959
Bibkey:
Cite (ACL):
Jonas Schäfer, Cezary Pilaszewicz, and Gerhard Wunder. 2026. Robust Text Watermarking for Large Language Models via Dual Semantic Embeddings. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 20266–20287, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Robust Text Watermarking for Large Language Models via Dual Semantic Embeddings (Schäfer et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.959.pdf