PostMark: A Robust Blackbox Watermark for Large Language Models

Fuente: arXiv
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Autores principales: Chang, Yapei, Krishna, Kalpesh, Houmansadr, Amir, Wieting, John, Iyyer, Mohit
Formato: Preprint
Publicado: 2024
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author Chang, Yapei
Krishna, Kalpesh
Houmansadr, Amir
Wieting, John
Iyyer, Mohit
author_facet Chang, Yapei
Krishna, Kalpesh
Houmansadr, Amir
Wieting, John
Iyyer, Mohit
contents The most effective techniques to detect LLM-generated text rely on inserting a detectable signature -- or watermark -- during the model's decoding process. Most existing watermarking methods require access to the underlying LLM's logits, which LLM API providers are loath to share due to fears of model distillation. As such, these watermarks must be implemented independently by each LLM provider. In this paper, we develop PostMark, a modular post-hoc watermarking procedure in which an input-dependent set of words (determined via a semantic embedding) is inserted into the text after the decoding process has completed. Critically, PostMark does not require logit access, which means it can be implemented by a third party. We also show that PostMark is more robust to paraphrasing attacks than existing watermarking methods: our experiments cover eight baseline algorithms, five base LLMs, and three datasets. Finally, we evaluate the impact of PostMark on text quality using both automated and human assessments, highlighting the trade-off between quality and robustness to paraphrasing. We release our code, outputs, and annotations at https://github.com/lilakk/PostMark.
format Preprint
id arxiv_https___arxiv_org_abs_2406_14517
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle PostMark: A Robust Blackbox Watermark for Large Language Models
Chang, Yapei
Krishna, Kalpesh
Houmansadr, Amir
Wieting, John
Iyyer, Mohit
Machine Learning
Artificial Intelligence
Computation and Language
Cryptography and Security
The most effective techniques to detect LLM-generated text rely on inserting a detectable signature -- or watermark -- during the model's decoding process. Most existing watermarking methods require access to the underlying LLM's logits, which LLM API providers are loath to share due to fears of model distillation. As such, these watermarks must be implemented independently by each LLM provider. In this paper, we develop PostMark, a modular post-hoc watermarking procedure in which an input-dependent set of words (determined via a semantic embedding) is inserted into the text after the decoding process has completed. Critically, PostMark does not require logit access, which means it can be implemented by a third party. We also show that PostMark is more robust to paraphrasing attacks than existing watermarking methods: our experiments cover eight baseline algorithms, five base LLMs, and three datasets. Finally, we evaluate the impact of PostMark on text quality using both automated and human assessments, highlighting the trade-off between quality and robustness to paraphrasing. We release our code, outputs, and annotations at https://github.com/lilakk/PostMark.
title PostMark: A Robust Blackbox Watermark for Large Language Models
topic Machine Learning
Artificial Intelligence
Computation and Language
Cryptography and Security
url https://arxiv.org/abs/2406.14517