The Provenance Horizon: Short Regulated Text Resists Reliable Watermarking Under Editing

Yanmin Zhao, Jikun Wu, Tengjiao Zheng, Yang Liu, Dongxin Guo, SM Yiu


Abstract
The EU Artificial Intelligence Act now requires providers to mark generated text so its origin can be checked. In regulated industries the duty is sharper: a marker must never flag third-party writing, survive routine review edits, and work on outputs often a sentence long. We call these the regulated-provenance triad and prove that no bounded-distortion watermark perturbing a model’s token distribution can satisfy all three below a critical length, the provenance horizon. The proof combines the Le Cam two-point method with a strong data-processing inequality for the edit channel; a matching achievability bound for the green-list family under a memoryless resampling channel makes the scaling order-tight. The barrier rises at negligible-distortion budgets, not at deployed ones. The contraction factor entering the bound is a proven upper bound for the memoryless resampling channel and a calibrated estimate for realistic paraphrase, under which we estimate most sentence-length regulated outputs fall below the horizon. Relocating provenance to a tamper-evident log read through a conformally calibrated retrieval test sidesteps the barrier: under exchangeable calibration its false-positive rate is at or below the target at every length. Coverage carries no guarantee and degrades under an adaptive editor.
Anthology ID:
2026.emnlp-main.1813
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
41316–41333
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1813/
DOI:
Bibkey:
Cite (ACL):
Yanmin Zhao, Jikun Wu, Tengjiao Zheng, Yang Liu, Dongxin Guo, and SM Yiu. 2026. The Provenance Horizon: Short Regulated Text Resists Reliable Watermarking Under Editing. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 41316–41333, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
The Provenance Horizon: Short Regulated Text Resists Reliable Watermarking Under Editing (Zhao et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.1813.pdf