MartDE: A Privacy-Preserving and Cost-Efficient Evaluation Framework for Data Marketplaces

The development of machine learning models increasingly relies on high-quality data that resides in private domains. To enable secure and value-driven data exchange under strict privacy regulations, federated learning (FL) has emerged as a key primitive by enabling the trading of model utilities instead of raw data. Among existing solutions, \textit{martFL} (CCS 2023) represents the most state-of-the-art FL-based data marketplace architecture, integrating privacy-preserving model evaluation, anomaly filtering, and verifiable trading protocols to enable robust and fair model utility exchange without revealing raw data. Despite its strengths, \textit{martFL} suffers from critical weaknesses at the evaluation layer, including plaintext score exposure and unverifiable and manipulable participant selection. To address these challenges, we propose \textit{MartDE}, a dedicated evaluation framework that augments FL data marketplaces with robust, privacy-preserving, and auditable mechanisms. \textit{MartDE} introduces encrypted utility scoring with client-side decryption to preserve score confidentiality, formally bounded anomaly filtering via squared similarity quantization, adaptive participant selection based on global model performance, and commitment-based verification to ensure consistency between declared and evaluated scores. We implement \textit{MartDE} and evaluate it across diverse datasets and adversarial conditions. Results show that \textit{MartDE} achieves superior accuracy, robustness, and cost-efficiency, providing a strong foundation for secure and trustworthy utility-driven data markets.