Con-ReCall: Detecting Pre-training Data in LLMs via Contrastive Decoding

Cheng Wang, Yiwei Wang, Bryan Hooi, Yujun Cai, Nanyun Peng, Kai-Wei Chang


Abstract
The training data in large language models is key to their success, but it also presents privacy and security risks, as it may contain sensitive information. Detecting pre-training data is crucial for mitigating these concerns. Existing methods typically analyze target text in isolation or solely with non-member contexts, overlooking potential insights from simultaneously considering both member and non-member contexts. While previous work suggested that member contexts provide little information due to the minor distributional shift they induce, our analysis reveals that these subtle shifts can be effectively leveraged when contrasted with non-member contexts. In this paper, we propose Con-ReCall, a novel approach that leverages the asymmetric distributional shifts induced by member and non-member contexts through contrastive decoding, amplifying subtle differences to enhance membership inference. Extensive empirical evaluations demonstrate that Con-ReCall achieves state-of-the-art performance on the WikiMIA benchmark and is robust against various text manipulation techniques.
Anthology ID:
2025.coling-main.68
Volume:
Proceedings of the 31st International Conference on Computational Linguistics
Month:
January
Year:
2025
Address:
Abu Dhabi, UAE
Editors:
Owen Rambow, Leo Wanner, Marianna Apidianaki, Hend Al-Khalifa, Barbara Di Eugenio, Steven Schockaert
Venue:
COLING
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
1013–1026
Language:
URL:
https://aclanthology.org/2025.coling-main.68/
DOI:
Bibkey:
Cite (ACL):
Cheng Wang, Yiwei Wang, Bryan Hooi, Yujun Cai, Nanyun Peng, and Kai-Wei Chang. 2025. Con-ReCall: Detecting Pre-training Data in LLMs via Contrastive Decoding. In Proceedings of the 31st International Conference on Computational Linguistics, pages 1013–1026, Abu Dhabi, UAE. Association for Computational Linguistics.
Cite (Informal):
Con-ReCall: Detecting Pre-training Data in LLMs via Contrastive Decoding (Wang et al., COLING 2025)
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PDF:
https://aclanthology.org/2025.coling-main.68.pdf