Yuetian Chen

Diffusion Language Models (DLMs) represent a promising alternative to autoregressive language models, using bidirectional masked token prediction. Yet their susceptibility to privacy leakage via Membership Inference Attacks (MIA) remains critically underexplored. This paper presents the first systematic investigation of MIA vulnerabilities in DLMs. Unlike the autoregressive models’ single fixed prediction pattern, DLMs’ multiple maskable configurations exponentially increase attack opportunities. This ability to probe many independent masks dramatically improves detection chances. To exploit this, we introduce SAMA (Subset-Aggregated Membership Attack), which addresses the sparse signal challenge through robust aggregation. SAMA samples masked subsets across progressive densities and applies sign-based statistics that remain effective despite heavy-tailed noise. Through inverse-weighted aggregation prioritizing sparse masks’ cleaner signals, SAMA transforms sparse memorization detection into a robust voting mechanism. Experiments on nine datasets show SAMA achieves 30% relative AUC improvement over the best baseline, with up to 8x improvement at low false positive rates. These findings reveal significant, previously unknown vulnerabilities in DLMs, necessitating the development of tailored privacy defenses.

Most membership inference attacks (MIAs) against Large Language Models (LLMs) rely on global signals, like average loss, to identify training data. This approach, however, dilutes the subtle, localized signals of memorization, reducing attack effectiveness. We challenge this global-averaging paradigm, positing that membership signals are more pronounced within localized contexts. We introduce WBC (Window-Based Comparison), which exploits this insight through a sliding window approach with sign-based aggregation. Our method slides windows of varying sizes across text sequences, with each window casting a binary vote on membership based on loss comparisons between target and reference models. By ensembling votes across geometrically spaced window sizes, we capture memorization patterns from token-level artifacts to phrase-level structures. Extensive experiments across eleven datasets demonstrate that WBC substantially outperforms established baselines, achieving higher AUC scores and 2-3 times improvements in detection rates at low false positive thresholds. Our findings reveal that aggregating localized evidence is fundamentally more effective than global averaging, exposing critical privacy vulnerabilities in fine-tuned LLMs.

We introduce a novel multi-agent system for automating story annotation through the generation of tailored prompts for a large language model (LLM). This system utilizes two agents: Agent A is responsible for generating prompts that identify the key information necessary for reconstructing the story, while Agent B reconstructs the story from these annotations and provides feedback to refine the initial prompts. Human evaluations and perplexity scores revealed that optimized prompts significantly enhance the model’s narrative reconstruction accuracy and confidence, demonstrating that dynamic interaction between agents substantially boosts the annotation process’s precision and efficiency. Utilizing this innovative approach, we created the “StorySense” corpus, containing 615 stories, meticulously annotated to facilitate comprehensive story analysis. The paper also demonstrates the practical application of our annotated dataset by drawing the story arcs of two distinct stories, showcasing the utility of the annotated information in story structure analysis and understanding.