synthpriv

Tabular data synthesis preserving differential privacy: generators (dp-gan with DP-SGD, dp-copula with pure DP), DP marginal ECDFs, benchmark and budget sweep, and an HTML privacy/utility report. Built on SDV, SDMetrics and Opacus for differential privacy (DP-SGD) with an RDP accountant.

The project evolves in cumulative phases, each with its own test suite and commit.

Implemented phases

Installation

python -m venv .venv
.venv/bin/pip install -e ".[dev]"   # (uses CUDA if available)

Dependencies: Python ≥ 3.10, numpy, pandas, scipy, scikit-learn, SDV < 2, SDMetrics, anonymeter, Opacus, click, Jinja2.

Quick start

Python API

from synthpriv import PrivacyPreservingSynthesizer
from synthpriv.privacy.mechanisms import DPSGD

privacy = DPSGD(epsilon=8.0, delta=1e-5)
synth = PrivacyPreservingSynthesizer(
    generator_key="dp-gan",
    generator_kwargs={"epochs": 100, "privacy": privacy, "random_state": 0},
    privacy_mechanism=privacy,
    utility_metrics=["ks_test", "correlation_mae", "ml_utility"],
    privacy_metrics=["nndr", "mia_auc"],
)
synthetic = synth.generate(real_df, num_rows=5000)   # fit + sample
report = synth.evaluate(real_df, synthetic)
report.save("report.html")                          # self-contained HTML report

# persist and regenerate without retraining
synth.save_model("demo_model.sz")
loaded = PrivacyPreservingSynthesizer.load_model("demo_model.sz")
loaded.sample(5000).to_csv("resample.csv", index=False)

# validate the DP guarantee
assurance = loaded.assert_dp()
print(assurance.status, assurance.message)

Note: do not pass random_state in generator_kwargs when the synthesizer already receives it in the constructor (conflict with the constructor's one).

CLI

# generate with a DP guarantee
synthpriv generate --data real.csv --epsilon 8 --rows 5000 --save demo_model.sz -o synthetic.csv

# regenerate without retraining (same accounted epsilon)
synthpriv sample --model demo_model.sz --rows 5000 -o resample.csv

# evaluate utility and privacy
synthpriv evaluate --real real.csv --synthetic synthetic.csv --epsilon 8 -o report.html

# epsilon <-> utility sweep (dp-gan or dp-copula)
synthpriv sweep --data real.csv --generator dp-copula --epsilons "0.1,0.5,1,2,5,50" -o sweep_report.html

# benchmark DP generator vs non-DP SDV generators (curves + utility gap)
synthpriv benchmark --data real.csv --generator dp-copula --epsilons "1,5,50" --baselines gaussian-copula -o bench.html

# audit that a persisted model's DP guarantee is not exceeded
synthpriv dpcheck --model demo_model.sz --tolerance 0.05

Reproducible demo

.venv/bin/python examples/demo.py [epsilon] [epochs] [ecdf_epsilon]

Trains dp-gan on a sample dataset, generates, evaluates, persists/reloads, regenerates and runs assert_dp. Artifacts under /tmp/synthpriv_demo/.

Differential privacy mechanics

• Only the discriminator trains with DP-SGD (gradient clipping + noise, Poisson sampling). The generator is post-processing of the discriminator, so the result is DP with the epsilon accounted by Opacus's RDP accountant.

• The real accumulated epsilon (accountant.get_epsilon()) is what is reported, not the target: it depends on sample size, epochs and resulting noise.

• assert_dp checks two conditions on a model (persisted or in memory):

  1. Step integrity: the DP steps accounted by the accountant == those executed by the discriminator during training.
  2. Budget: measured epsilon ≤ declared epsilon × (1 + tolerance).

  If either fails, the state is fail and the RDP guarantee is in question.

Mechanisms

• NoPrivacy() — no formal guarantee (only empirical mitigation + risk metrics).
• DPSGD(epsilon=1.0, delta=1e-5) — DP-SGD (Opacus) for the dp-gan generator; it also configures the total budget for the dp-copula generator (pure DP, δ=0). noise_multiplier: if set, that noise is used; otherwise Opacus computes it to reach the budget. After training, used_noise_multiplier holds the applied value.

Generators

dp-copula

Parametric model that attacks the dp-gan weak spot (the dependence structure) with pure DP (δ=0, all sub-mechanisms are Laplace). The total budget is split into margins_fraction (≈ default 0.4, private ECDFs per column), corr_fraction (≈ default 0.4, per-entry Laplace-perturbed correlation matrix projected to PSD) and the rest into categorical frequencies. On purely numeric datasets the whole remainder goes to the copula. Benchmark on correlated data: learned correlation ≈0.61 vs 0.60 real (dp-gan ≈0.72-0.83) at ε=1-5. In the CLI: synthpriv generate --method dp-copula --epsilon E.

dp-gan

Only the discriminator sees real data and trains with DP-SGD. Relevant hyperparameters:

• privacy — DPSGD mechanism with target ε/δ.
• num_modes (3) — ModeEncoder Gaussian Mixture per numeric column; 1 = z-score.
• numeric ("mode") — numeric encoding: "mode" (mode-specific, mix of Gaussians) or "uniform" (gaussianized percentile range Φ⁻¹(rank) + empirical quantile). "uniform" handles tails much better and is the recommended option when the marginal matters; its inverse interpolates between quantiles (does not return exact real values).
• rectify_marginals (False) — only with numeric="uniform": rectifies at sample time the continuous marginals to the real ECDF (monotone per-column transformation, preserves the copula). Guarantees KS ≈ 1 for the numerics; it shares the per-column empirical-quantile trade-off (utility vs. leakage) documented in Limitations.
• condition_column (None) — column that conditions generation; None picks the most imbalanced one (lowest entropy) so minority classes do not collapse.
• aux_lambda (1.0) — weight of auxiliary losses (classifier + class consistency).
• generator_steps (2) — generator steps per discriminator step (the DP budget only counts the discriminator).
• label_smoothing (0.0) — discriminator label smoothing; useful for stability.
• ecdf_epsilon (None) — DP budget for the marginals (only with numeric="uniform"): builds a private ECDF per column (Laplace histogram, ε per column = ecdf_epsilon / #numeric, parallel composition by bins). The synthesizer's total guarantee is the sequential composition epsilon(accumulated) + ecdf_epsilon (additive and exact: the ECDF is pure DP, δ=0), exposed in the report as accountant.ecdf_epsilon / accountant.total_epsilon. With None the ECDF is the raw empirical one (no formal guarantee on the marginal). CLI: synthpriv generate --epsilon E --ecdf-epsilon EE.
• ecdf_bounds (None) — public support (min, max) of the private ECDFs. With bounds the guarantee is strictly pure DP (fixed grid, no data-derived range); without them the support is derived from the 0.001/0.999 quantiles (with margin) and a warning documents that nuance.
• Budget split — from synthpriv import split_budget; b = split_budget(total=10.0, margins_fraction=0.3) returns b.train (for epsilon) and b.margins (for ecdf_epsilon), with b.total = train + margins. The dp-gan total is exactly additive.

Hardening phase results (tabular dataset with real correlations, 1500 rows, numeric="uniform" + rectify_marginals): KS ≈ 1.0 on all three numerics for ε = 1/5/25 and ml_utility on par with SDV's Gaussian copula (≈0.35). The copula still wins on correlations (corrMAE ≈0.02 vs ≈0.2–0.37): the dependence structure is what an MLP DP-GAN learns least on small datasets (see Limitations).

Metrics

• Utility: KS (distributions), correlation MAE, ML utility (TSTR).
• Privacy: NNDR (distance to nearest real neighbor), inference attack AUC (MIA) and anonymeter attacks.

Tests

.venv/bin/python -m pytest -q              # fast (default)
.venv/bin/python -m pytest -m slow -q      # trains deep models

• test_registry, test_generators, test_metrics, test_pipeline, test_cli
• test_dp (end-to-end DP + minority class coverage)
• test_dp_matrix (dp-copula in sweep/benchmark: model/kind/measured epsilon)
• test_sweep (ε-utility sweep, dp-gan/dp-copula)
• test_benchmark (DP vs baselines: structure, gaps, reports)
• test_serialization (persistence/reload)
• test_assurance (DP step integrity and budget)

Limitations

• dp-gan is an MLP GAN: for small numeric/categorical datasets, not for images or sequences.
• The DP guarantee relies on Opacus's RDP accountant and Poisson sampling; formal audit with dedicated libraries is out of scope.
• assert_dp validates the integrity of the training DP-SGD (steps + budget). If you also use ecdf_epsilon, the synthesizer's total guarantee is the composition epsilon(accumulated) + ecdf_epsilon (additive and exact: the ECDF is pure DP, δ=0); the report and the assert_dp message show it.
• With ecdf_epsilon, the marginal budget is split equally across columns and the support of each ECDF is trimmed to the empirical 0.001/0.999 quantiles (+margin): exact extremes are neither emitted nor published, at the cost of a slight generated-range trim.
• Although dp-gan respects the budget, real utility at low ε depends on the dataset (see the synthpriv sweep sweep).
• The dependence structure (correlations) is the dp-gan weak spot: partially learned and noisy on small datasets; there copulas (SDV) are more accurate.
• With numeric="uniform" the marginal is tied to the real empirical quantiles (interpolated), which gives strong utility but shares per-column information; use it with rectify_marginals=True only when marginal utility is the priority over that consideration.

Privacy note

Synthetic data without DP is not guaranteed anonymization. The report suggests which ε level to use and which empirical risk is measured, but formal protection only comes from training with a DP mechanism (DPSGD + dp-gan/dp-copula) and verifying it with assert_dp.