  Recent advances in large language models (LLMs) and the intensifying
popularity of ChatGPT-like applications have blurred the boundary of
high-quality text generation between humans and machines. However, in addition
to the anticipated revolutionary changes to our technology and society, the
difficulty of distinguishing LLM-generated texts (AI-text) from human-generated
texts poses new challenges of misuse and fairness, such as fake content
generation, plagiarism, and false accusations of innocent writers. While
existing works show that current AI-text detectors are not robust to LLM-based
paraphrasing, this paper aims to bridge this gap by proposing a new framework
called RADAR, which jointly trains a robust AI-text detector via adversarial
learning. RADAR is based on adversarial training of a paraphraser and a
detector. The paraphraser's goal is to generate realistic content to evade
AI-text detection. RADAR uses the feedback from the detector to update the
paraphraser, and vice versa. Evaluated with 8 different LLMs (Pythia, Dolly
2.0, Palmyra, Camel, GPT-J, Dolly 1.0, LLaMA, and Vicuna) across 4 datasets,
experimental results show that RADAR significantly outperforms existing AI-text
detection methods, especially when paraphrasing is in place. We also identify
the strong transferability of RADAR from instruction-tuned LLMs to other LLMs,
and evaluate the improved capability of RADAR via GPT-3.5-Turbo.
