CITED: A Decision Boundary-Aware Signature for GNNs Towards Model Extraction Defense

2026-02-23

AI Summary

This work addresses the vulnerability of Graph Neural Networks (GNNs) in Machine Learning as a Service (MLaaS) settings to model extraction attacks, wherein adversaries construct functionally similar surrogate models through query access. To counter this threat, the paper introduces CITED, a novel ownership verification framework that, for the first time, embeds decision boundary-aware signatures simultaneously at both the embedding and label layers. Notably, CITED operates without requiring auxiliary models and incurs no degradation in downstream task performance. Empirical evaluations demonstrate that CITED substantially outperforms existing watermarking and fingerprinting approaches, achieving superior defense efficacy, robustness against adaptive attacks, and model efficiency.

Technology Category

• Machine Learning: Adversarial Learning & Robustness
• Computer Vision: Adversarial Attacks & Robustness
• Natural Language Processing: Fact-Checking / Misinformation Detection (NLP Focus)

Application Category

• Graph Algorithms and Modeling for the Web: Graph neural networks and deep learning approaches for Web-related graphs
• Search and Retrieval-Augmented AI: Web learning to rank, online learning, and counterfactual learning for ranking
• User Modeling, Personalization and Recommendation: Attacks and countermeasures in recommendation systems

Abstract

Graph neural networks (GNNs) have demonstrated superior performance in various applications, such as recommendation systems and financial risk management. However, deploying large-scale GNN models locally is particularly challenging for users, as it requires significant computational resources and extensive property data. Consequently, Machine Learning as a Service (MLaaS) has become increasingly popular, offering a convenient way to deploy and access various models, including GNNs. However, an emerging threat known as Model Extraction Attacks (MEAs) presents significant risks, as adversaries can readily obtain surrogate GNN models exhibiting similar functionality. Specifically, attackers repeatedly query the target model using subgraph inputs to collect corresponding responses. These input-output pairs are subsequently utilized to train their own surrogate models at minimal cost. Many techniques have been proposed to defend against MEAs, but most are limited to specific output levels (e.g., embedding or label) and suffer from inherent technical drawbacks. To address these limitations, we propose a novel ownership verification framework CITED which is a first-of-its-kind method to achieve ownership verification on both embedding and label levels. Moreover, CITED is a novel signature-based method that neither harms downstream performance nor introduces auxiliary models that reduce efficiency, while still outperforming all watermarking and fingerprinting approaches. Extensive experiments demonstrate the effectiveness and robustness of our CITED framework. Code is available at: https://github.com/LabRAI/CITED.

Problem

• Graph Neural Networks
• Model Extraction Attacks
• Machine Learning as a Service
• Ownership Verification
• Decision Boundary

Innovation

• model extraction defense
• graph neural networks
• ownership verification
• decision boundary-aware signature
• MLaaS security