Stealix: Model Stealing via Prompt Evolution

Fuente: arXiv
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Autori principali: Zhuang, Zhixiong, Wang, Hui-Po, Nicolae, Maria-Irina, Fritz, Mario
Natura: Preprint
Pubblicazione: 2025
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author Zhuang, Zhixiong
Wang, Hui-Po
Nicolae, Maria-Irina
Fritz, Mario
author_facet Zhuang, Zhixiong
Wang, Hui-Po
Nicolae, Maria-Irina
Fritz, Mario
contents Model stealing poses a significant security risk in machine learning by enabling attackers to replicate a black-box model without access to its training data, thus jeopardizing intellectual property and exposing sensitive information. Recent methods that use pre-trained diffusion models for data synthesis improve efficiency and performance but rely heavily on manually crafted prompts, limiting automation and scalability, especially for attackers with little expertise. To assess the risks posed by open-source pre-trained models, we propose a more realistic threat model that eliminates the need for prompt design skills or knowledge of class names. In this context, we introduce Stealix, the first approach to perform model stealing without predefined prompts. Stealix uses two open-source pre-trained models to infer the victim model's data distribution, and iteratively refines prompts through a genetic algorithm, progressively improving the precision and diversity of synthetic images. Our experimental results demonstrate that Stealix significantly outperforms other methods, even those with access to class names or fine-grained prompts, while operating under the same query budget. These findings highlight the scalability of our approach and suggest that the risks posed by pre-trained generative models in model stealing may be greater than previously recognized.
format Preprint
id arxiv_https___arxiv_org_abs_2506_05867
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Stealix: Model Stealing via Prompt Evolution
Zhuang, Zhixiong
Wang, Hui-Po
Nicolae, Maria-Irina
Fritz, Mario
Cryptography and Security
Machine Learning
Model stealing poses a significant security risk in machine learning by enabling attackers to replicate a black-box model without access to its training data, thus jeopardizing intellectual property and exposing sensitive information. Recent methods that use pre-trained diffusion models for data synthesis improve efficiency and performance but rely heavily on manually crafted prompts, limiting automation and scalability, especially for attackers with little expertise. To assess the risks posed by open-source pre-trained models, we propose a more realistic threat model that eliminates the need for prompt design skills or knowledge of class names. In this context, we introduce Stealix, the first approach to perform model stealing without predefined prompts. Stealix uses two open-source pre-trained models to infer the victim model's data distribution, and iteratively refines prompts through a genetic algorithm, progressively improving the precision and diversity of synthetic images. Our experimental results demonstrate that Stealix significantly outperforms other methods, even those with access to class names or fine-grained prompts, while operating under the same query budget. These findings highlight the scalability of our approach and suggest that the risks posed by pre-trained generative models in model stealing may be greater than previously recognized.
title Stealix: Model Stealing via Prompt Evolution
topic Cryptography and Security
Machine Learning
url https://arxiv.org/abs/2506.05867