SeungYeop Baik
2025
TrapDoc: Deceiving LLM Users by Injecting Imperceptible Phantom Tokens into Documents
Hyundong Jin
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Sicheol Sung
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Shinwoo Park
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SeungYeop Baik
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Yo-Sub Han
Findings of the Association for Computational Linguistics: EMNLP 2025
The reasoning, writing, text-editing, and retrieval capabilities of proprietary large language models (LLMs) have advanced rapidly, providing users with an ever-expanding set of functionalities. However, this growing utility has also led to a serious societal concern: the over-reliance on LLMs. In particular, users increasingly delegate tasks such as homework, assignments, or the processing of sensitive documents to LLMs without meaningful engagement. This form of over-reliance and misuse is emerging as a significant social issue. In order to mitigate these issues, we propose a method injecting imperceptible phantom tokens into documents, which causes LLMs to generate outputs that appear plausible to users but are in fact incorrect. Based on this technique, we introduce TrapDoc, a framework designed to deceive over-reliant LLM users. Through empirical evaluation, we demonstrate the effectiveness of our framework on proprietary LLMs, comparing its impact against several baselines. TrapDoc serves as a strong foundation for promoting more responsible and thoughtful engagement with language models.
CodeComplex: Dataset for Worst-Case Time Complexity Prediction
SeungYeop Baik
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Joonghyuk Hahn
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Jungin Kim
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Aditi
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Mingi Jeon
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Yo-Sub Han
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Sang-Ki Ko
Findings of the Association for Computational Linguistics: EMNLP 2025
Reasoning ability of large language models (LLMs) is a crucial ability,especially in complex decision-making tasks. One significant task to show LLMs’reasoning capability is code time complexity prediction, which involves variousintricate factors such as the input range of variables and conditional loops.Current benchmarks fall short of providing a rigorous assessment due to limiteddata, language constraints, and insufficient labeling. They do not consider timecomplexity based on input representation and merely evaluate whether predictionsfall into the same class, lacking a measure of how close incorrect predictionsare to the correct ones.To address these dependencies, we introduce CodeComplex, the first robust andextensive dataset designed to evaluate LLMs’ reasoning abilities in predictingcode time complexity. CodeComplex comprises 4,900 Java codes and an equivalentnumber of Python codes, overcoming language and labeling constraints, carefullyannotated with complexity labels based on input characteristics by a panel ofalgorithmic experts. Additionally, we propose specialized evaluation metrics forthe reasoning of complexity prediction tasks, offering a more precise andreliable assessment of LLMs’ reasoning capabilities. We release our dataset andbaseline models publicly to encourage the relevant (NLP, SE, and PL) communitiesto utilize and participate in this research. Our code and data are available athttps://github.com/sybaik1/CodeComplex.
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- Yo-Sub Han 2
- Aditi 1
- Joonghyuk Hahn 1
- Mingi Jeon 1
- Hyundong Jin 1
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