DP-ES: Differentially Private Evolution Strategies for Prompt Optimization
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Abstract (arXiv)
Token-level differentially private (DP) prompt optimization methods such as DP-OPT can become unstable under tight privacy budgets: on GSM8K, DP-OPT obtains 49.5±28.5% across 30 runs, and a logged search trajectory reveals prompt-template drift and noise-sensitive irreversible choices. We diagnose these as structural consequences of greedy token-by-token construction over privately aggregated counts. We then propose DP-ES (Differentially Private Evolution Strategies), a structurally cleaner alternative that maintains a population of full prompts, mutates them via LLM calls that never access the private dataset, and spends privacy only on sampled-Gaussian evaluation; deterministic or Gumbel-smoothed selection is post-processing. Under a conservative (varepsilon≤1.0,δ=10-5) guarantee, DP-ES achieves 88.1% on GSM8K (+38.6 pp over DP-OPT, approximately 9 times lower standard deviation), 99.7% on MedQA, 73.5% on BANKING77, and 86.8% on Alpaca. It is also 2.5 times faster in wall-clock time and uses 3.3 times fewer logged private-data call groups than DP-OPT. Selection and population ablations, implementation-level noise checks, and a 200-profile exact-match memorization stress test complement the formal guarantee. Scope: Our experiments establish optimization robustness under DP noise, especially where prompt structure is critical; end-to-end validation on genuinely sensitive, non-saturated deployment data remains future work.
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References · 21
- 2020Language Models are Few-Shot Learnerscited by 32,419
- 2022Training language models to follow instructions with human feedbackcited by 15,971
- 2021Training Verifiers to Solve Math Word Problemscited by 10,109
- 2016Deep Learning with Differential Privacycited by 2,728
- 2020What Disease does this Patient Have? A Large-scale Open Domain Question Answering Dataset from Medical Examscited by 1,356
- 2022Large Language Models Are Human-Level Prompt Engineerscited by 1,045
- 2023Promptbreeder: Self-Referential Self-Improvement Via Prompt Evolutioncited by 551
- 2023DecodingTrust: A Comprehensive Assessment of Trustworthiness in GPT Modelscited by 518
- 2020Efficient Intent Detection with Dual Sentence Encoderscited by 433
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- 2020Auditing Differentially Private Machine Learning: How Private is Private SGD?cited by 218
9 more
- 2021Adversary Instantiation: Lower Bounds for Differentially Private Machine Learningcited by 199
- 2023Practical Membership Inference Attacks against Fine-tuned Large Language Models via Self-prompt Calibrationcited by 98
- 2023Privacy-Preserving In-Context Learning with Differentially Private Few-Shot Generationcited by 96
- 2024Differentially Private Synthetic Data via Foundation Model APIs 2: Textcited by 76
- 2023Differentially Private Synthetic Data via Foundation Model APIs 1: Imagescited by 65
- 2023DP-OPT: Make Large Language Model Your Privacy-Preserving Prompt Engineercited by 57
- 2024Privacy Preserving Prompt Engineering: A Surveycited by 25
- 2025SoK: The Privacy Paradox of Large Language Models: Advancements, Privacy Risks, and Mitigationcited by 19
- 2025Private LoRA Fine-tuning of Open-Source LLMs with Homomorphic Encryptioncited by 7
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