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Protecting Your LLMs with Information Bottleneck
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Proposes IBProtector, a lightweight trainable extractor guided by an information-bottleneck objective that masks and perturbs jailbreak prompts so a frozen target LLM refuses harmful requests while still answering benign ones.
Problem
LLMs remain vulnerable to token-level (GCG) and prompt-level (PAIR) jailbreaks; existing defenses rely on random perturbations, costly semantic parsing, or fine-tuning of the target model.
Approach
Applies the information bottleneck principle to jailbreak defense: a small trainable extractor (TinyLlama-1.1B with an MLP head) produces Bernoulli masks that keep only response-relevant prompt tokens and replace the rest with a period, trained with a KL-based compactness bound, continuity loss, and an informativeness loss computed through the frozen target LLM; an RL variant is proposed for black
Key results
- On PAIR attacks against Vicuna-13B, IBProtector reduces ASR from 87.5% to 19.2%, and on GCG attacks against LLaMA-2-7b-chat from 27.5% to 0.8% (original attack vs. IBProtector).
- IBProtector keeps benign answering rate high on TriviaQA (96.5% on Vicuna-13B vs. 97.8% undefended).
- On EasyJailbreak transfer attacks against Vicuna-13B, ASR drops from 88.6% to 18.9% without retraining on those attacks.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Apply IBProtector instead of the strongest reported baseline | Vicuna-13B · AdvBench PAIR | ASR: 20.0% -> 19.2% | Helped |
| Apply IBProtector instead of the strongest reported baseline | LLaMA-2-7B · AdvBench PAIR | ASR: 40.0% -> 16.7% | Helped |
| Apply IBProtector instead of the strongest reported baseline | Vicuna-13B · AdvBench GCG | ASR: 1.7% -> 1.7% | No clear effect |
| Apply IBProtector instead of the strongest reported baseline | LLaMA-2-7B · AdvBench GCG | ASR: 4.2% -> 0.8% | Helped |
| Apply IBProtector instead of the strongest reported baseline | Vicuna-13B · TriviaQA | BAR: 95.7% -> 96.5% | Helped |
| Apply IBProtector instead of the strongest reported baseline | LLaMA-2-7B · TriviaQA | BAR: 97.4% -> 97.0% | Hurt |
| Transfer the trained extractor to EasyJailbreak attacks | Vicuna-13B · EasyJailbreak transfer | ASR: 26.8% -> 18.9% | Helped |
| Transfer the trained extractor to EasyJailbreak attacks | LLaMA-2-7B · EasyJailbreak transfer | ASR: 2.2% -> 0.7% | Helped |
| Use IBProtector rather than Semantic Smooth against adaptive PAIR | Vicuna-13B · Adaptive PAIR | ASR: 86.0% -> 52.0% | Helped |
| Use IBProtector rather than Semantic Smooth against adaptive PAIR | LLaMA-2-7B · Adaptive PAIR | ASR: 44.0% -> 36.0% | Helped |
| Vary the continuity weight lambda (ablation) | IBProtector · PAIR attacks on Vicuna-13B | ASR | No clear effect |
| Increase the compactness weight alpha (ablation) | IBProtector · PAIR attacks on Vicuna-13B | ASR | Hurt |
Surprising findings
- Smooth-style random perturbation defenses nearly lose their effect or even increase ASR on stealthier EasyJailbreak attacks, while the learned extractor transfers.
Limitations
- Requires shared tokenizer and gradient access to the target LLM, so it is not directly applicable to closed models like GPT-4; RL variant is proposed but not tested.
- Extracted sub-prompts are non-fluent and hard for humans to interpret; defense relies on the target model's own safety alignment.
- Evaluated only on text and small-scale attack sets (e.g., 120 test instances, 50 adaptive instances).
Experimental setup
Datasets: AdvBench TriviaQA EasyJailbreak
Benchmarks: AdvBench TriviaQA EasyJailbreak
Metrics: attack success rate harm score GPT-4 score benign answering rate
Baselines: Fine-tuning Unlearning LLM Self Defense Smooth LLM RA-LLM Semantic Smooth
Builds on: information bottleneck variational information bottleneck SmoothLLM GCG PAIR
Closest papers by meaning
- RigorLLM: Resilient Guardrails for Large Language Models against Undesired Content (ICML 2024 · similarity 0.89)
- Bits Leaked per Query: Information-Theoretic Bounds for Adversarial Attacks on LLMs (NeurIPS 2025 · similarity 0.89)
- Safeguarding LLMs via Model-Agnostic Latent Safety Signals from Dark Knowledge (NeurIPS 2026 · similarity 0.88)
- Look Before You Leap: Enhance Attention and Vigilance Regarding Harmful Content with GuidelineLLM (AAAI 2025 · similarity 0.88)
- Soft Prompt Threats: Attacking Safety Alignment and Unlearning in Open-Source LLMs through the Embedding Space (NeurIPS 2024 · similarity 0.87)
- Jailbreak Antidote: Runtime Safety-Utility Balance via Sparse Representation Adjustment in Large Language Models (ICLR 2025 · similarity 0.87)
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