Robust Distortion-free Watermarks for Language Models
Paper · 2023 · Rohith Kuditipudi, John Thickstun, Tatsunori Hashimoto et al.
Summary
The paper tackles provenance of LM-generated text. It seeks a watermark that leaves the model's output distribution unchanged (distortion-free), can be verified without access to the model or prompt (agnostic), and survives editing (robust). Earlier hashing-based schemes (Kirchenbauer et al., Aaronson, Christ et al.) fall short on at least one of these. In the proposed protocol, the provider and detector share a secret key that encodes a sequence of random numbers. Generation deterministically turns this sequence into a model sample, using either inverse transform sampling (ITS) or exponential minimum sampling (EXP). A shift wrapper starts from a random offset so that outputs vary across calls. Detection aligns a suspect text against the key sequence using robust sequence-alignment costs, which yields a p-value. Experiments cover OPT-1.3B, LLaMA-7B and Alpaca-7B. The EXP variant is the strongest, staying detectable from short passages even after heavy random edits. Detection is harder on low-entropy instruction responses. The work matters because it shows watermarking need not trade output quality for robustness, and the code is publicly released.
Key points
- Robustness to edits: On OPT-1.3B and LLaMA-7B, 35 tokens suffice for detection at p ≤ 0.01, even with 40–50% of tokens randomly substituted, inserted or deleted.
- Robustness to translation: Text paraphrased by round-trip translation through French or Russian remains detectable from about 50 tokens.
- Alpaca-7B case study: Only about 25% of instruction responses (median length around 100 tokens) are detectable at p ≤ 0.01, and robustness to automated paraphrasing is weaker.
- Detection runtimes: With key length n = 10,000 on an Apple M2 laptop, the test statistics take about 0.004 s (ITS), 0.60 s (ITS-edit), 2.20 s (EXP) and 3.21 s (EXP-edit).
- Practical recommendations: A small key (n = 256) does not noticeably harm text quality. EXP-edit is advised when robustness matters, and ITS when high-throughput detection matters, since it reduces to maximum inner-product search. Code is at github.com/jthickstun/watermark.
Institutions
Fields, topics and concepts
📚 Shelves 4The field of science this work belongs to (OpenAlex fields).Computer Science · 18,614 worksArtificial Intelligence · 17,965 worksComputer Vision and Pattern Recognition · 3,486 worksHardware and Architecture · 167 works
🧭 Topics 1Research subjects and languages the work is about.Language models & pretraining · 3,894 works
Cite
Cite as Rohith Kuditipudi, John Thickstun, Tatsunori Hashimoto and Percy Liang. 2023. Robust Distortion-free Watermarks for Language Models. arXiv:2307.15593.
@misc{kuditipudi2023robust,
title = {{Robust Distortion-free Watermarks for Language Models}},
author = {Rohith Kuditipudi, John Thickstun, Tatsunori Hashimoto and Percy Liang},
year = {2023},
doi = {10.48550/arxiv.2307.15593},
eprint = {2307.15593},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2307.15593}
}References
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