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Alina Oprea

11 accepted papers

2026

Beware Untrusted Simulators -- Reward-Free Backdoor Attacks in Reinforcement Learning

ICLR 2026poster

Simulated environments are a key piece in the success of Reinforcement Learning (RL), allowing practitioners and researchers to train decision making agents without running expensive experiments on real hardware. Simulators remain a security blind spot, however, enabling adversarial developers to al…

Cited by 0SourceScholar
2026

Black-Box Privacy Attacks on Shared Representations in Multitask Learning

ICLR 2026poster

The proliferation of diverse data across users and organizations has driven the development of machine learning methods that enable multiple entities to jointly train models while minimizing data sharing. Among these, *multitask learning* (MTL) is a powerful paradigm that leverages similarities amon…

Cited by 0SourceScholar
2026

When Anonymity Breaks: Identifying Models Behind Text-to-Image Leaderboards

CVPR 2026

Text-to-image (T2I) models are increasingly popular, producing a large share of AI-generated images online. To compare model quality, voting-based leaderboards have become the standard, relying on anonymized model outputs for fairness. In this work, we show that such anonymity can be easily broken.

Cited by 0SourceScholar
2025

Adversarial Inception Backdoor Attacks against Reinforcement Learning

ICML 2025poster

Recent works have demonstrated the vulnerability of Deep Reinforcement Learning (DRL) algorithms against training-time, backdoor poisoning attacks. The objectives of these attacks are twofold: induce pre-determined, adversarial behavior in the agent upon observing a fixed trigger during deployment w…

Cited by 0SourcePDFScholar
2024

Chameleon: Increasing Label-Only Membership Leakage with Adaptive Poisoning

ICLR 2024poster

The integration of Machine Learning (ML) in numerous critical applications introduces a range of privacy concerns for individuals who provide their datasets for ML training purposes. One such privacy risk is Membership Inference (MI), in which an adversary seeks to determine whether a particular dat…

Cited by 7SourcePDFScholar
2024

One-shot Empirical Privacy Estimation for Federated Learning

ICLR 2024oral

Privacy estimation techniques for differentially private (DP) algorithms are useful for comparing against analytical bounds, or to empirically measure privacy loss in settings where known analytical bounds are not tight. However, existing privacy auditing techniques usually make strong assumptions o…

2024

SleeperNets: Universal Backdoor Poisoning Attacks Against Reinforcement Learning Agents

NeurIPS 2024poster

Reinforcement learning (RL) is an actively growing field that is seeing increased usage in real-world, safety-critical applications -- making it paramount to ensure the robustness of RL algorithms against adversarial attacks. In this work we explore a particularly stealthy form of training-time atta…

Cited by 2SourcePDFScholar
2024

User Inference Attacks on Large Language Models

EMNLP 2024main

Text written by humans makes up the vast majority of the data used to pre-train and fine-tune large language models (LLMs). Many sources of this data—like code, forum posts, personal websites, and books—are easily attributed to one or a few “users”. In this paper, we ask if it is possible to infer i…

Cited by 28SourcePDFScholar
2023

Unleashing the Power of Randomization in Auditing Differentially Private ML

NeurIPS 2023poster

We present a rigorous methodology for auditing differentially private machine learning by adding multiple carefully designed examples called canaries. We take a first principles approach based on three key components. First, we introduce Lifted Differential Privacy (LiDP) that expands the definition…

Cited by 28SourcePDFScholar
2020

Auditing Differentially Private Machine Learning: How Private is Private SGD?

NeurIPS 2020poster

We investigate whether Differentially Private SGD offers better privacy in practice than what is guaranteed by its state-of-the-art analysis. We do so via novel data poisoning attacks, which we show correspond to realistic privacy attacks. While previous work (Ma et al., arXiv 2019) proposed this co…

2019

Differentially Private Fair Learning

ICML 2019oral

Motivated by settings in which predictive models may be required to be non-discriminatory with respect to certain attributes (such as race), but even collecting the sensitive attribute may be forbidden or restricted, we initiate the study of fair learning under the constraint of differential privacy…

Cited by 202SourcePDFScholar