🧑💻 Zhipeng “Zippo” He 何志鹏 @ School of Information Systems
Queensland University of Technology
PhD Final Seminar
October 08, 2025
$ \(\newcommand{\one}{\unicode{x1d7d9}}\) “54F” $
💡 Background & Motivation
🎯 Research Problem
🧩 Objective 1 — Foundation of Imperceptibility
Defining imperceptible properties on tabular data.
📊 Objective 2 — Benchmark of Tabular Attacks
Systematic evaluation framework for existing adversarial attacks.
⚙️ Objective 3 — Generative VAE-based Attack
Unified treatment of categorical & numerical features in latent space.
🌟 Conclusion & Future Directions
From conceptual clarity → systematic evaluation → practical robustness.
💡 Background & Motivation

In Computer Science (CS), robustness has been more formally defined by the IEEE (IEEE 2008) as:
the degree to which a system or component can function correctly in the presence of invalid inputs or stressful conditions.
In Machine Learning (ML), robustness refers to:
the ability of a model to perform well on unseen or new data or variations in the input.

Adversarial robustness = robustness against worst-case, deliberately crafted perturbations (Szegedy et al. 2014)
An adversarial attack is a method to generate adversarial examples.
Adversarial examples are specialised inputs created with the purpose of confusing a neural network, resulting in the misclassification of a given input. These notorious inputs are indistinguishable to the human eye but cause the network to fail to identify the contents of the image. (Goodfellow, Shlens, and Szegedy 2015)

For example, when applying Fast Gradient Sign Method (FGSM), we can generate an adversarial example:

Even small, imperceptible perturbations can cause a model to make confidently incorrect predictions.



Tabular data powers critical real-world systems: finance (Lunghi et al. 2023), healthcare (Sun et al. 2018), cybersecurity (D. Li et al. 2023)
Image (unstructured)
• High-dimensional, homogeneous
• Continuous pixels
Tabular (structured) (Borisov et al. 2024)
• Lower-dimensional, heterogeneous
• Numerical + categorical
• Feature dependencies

Would existing adversarial attacks still work on tabular data without adaptations?
Adversarial attacks can be described along four dimensions (Papernot et al. 2016; Biggio and Roli 2018; Assion et al. 2019; Pelekis et al. 2025):


Privacy Attack (training-time) out of scope
Poison Attack (training-time) out of scope
Evasion Attack (test-time)
White-Box Attacks ✅
Grey-Box Attacks ❌
Black-Box Attacks ❌
White-box attacks represent the worst-case scenarios (Papernot et al. 2016)
👉 If a model is robust under white-box attacks, it can handle any other type of attacks.
Bounded attacks ✅

Unbounded attacks ✅

Confidence Reduction ❌
Nontargeted Misclassification ✅
Targeted Misclassification ❌
Source/Target Misclassification ❌
Given a credit score classification systems \(f: \mathbb{X}\to \mathbb{Y}\) with three classes \(\mathbb{Y} = \{\)Poor, Standard, Good\(\}\), select an input instance \(\boldsymbol{x}\in\mathbb{X}\) to craft a adversarial example \(\boldsymbol{x}^{adv}\):
Poor, 90% confidence) → \(\boldsymbol{x}^{adv}\) (Poor, 50% confidence)Poor) → \(\boldsymbol{x}^{adv}\) (a different class, Standard or Good)Poor or Standard) → \(\boldsymbol{x}^{adv}\) (specific class Good)Poor) → \(\boldsymbol{x}^{adv}\) (specific class Good)
Most existing benchmarks focus on:
The only tabular benchmark focuses on a single attack method (Simonetto, Ghamizi, and Cordy 2024), leaving comprehensive tabular evaluation underexplored.
Researchers have been working on making models more robust to adversarial attacks on unstructured data. However, researchers have rarely investigated adversarial robustness for tabular data.
How can one construct predictive models that are robust to adversarial attacks for tabular data?
From the definition of adversarial examples, we have two central challenges:
Imperceptibility — Only limited work on this (Ballet et al. 2019; Chernikova and Oprea 2022).
❓ Can we use the same imperceptibility concept as in Computer Vision for tabular data?

In Computer Vision, adversarial perturbations must be “indistinguishable to the human eye” (Goodfellow, Shlens, and Szegedy 2015) — the adversarial image should look identical to the original.
This is formalised using bounded perturbations under norms (e.g., \(\ell_\infty\)) (Madry et al. 2018). These constraints limit the size of pixel-level changes.

👉 CV-style definitions of imperceptibility (pixel norms) do not transfer to tabular data.
Goal: adversarial examples should not just small perturbations, but also remain realistic.
Imperceptibility in tabular data means perturbations must preserve:
Statistical consistency → numerical features follow realistic distributions
Semantic validity → categorical values remain logically consistent
Structural integrity → dependencies between features are not violated
🎯 Research Problem
RQ1: What properties can be used to define the imperceptibility of adversarial attacks on tabular data?
Unlike images, tabular datasets require definitions that account for
This question establishes the conceptual foundations of imperceptibility.
Objective 1: Identify and formalise the set of properties of imperceptible adversarial attacks on tabular data.
RQ2: How do existing adversarial attacks perform under both effectiveness and tabular-specific imperceptibility criteria?
Two dimensions:
1. Ability to misclassify predictive models (effectiveness)
2. Extent to which perturbations achieve minimal perturbation and statistical consistency (imperceptibility)
Sub-questions:
Objective 2: Develop an evaluation framework to benchmark adversarial attacks on tabular data.
RQ3: How can new adversarial attacks on tabular data be designed to generate both effective and imperceptible adversarial examples?
Sub-questions:
Objective 3: Design new adversarial attack that unify effectiveness with tabular-specific imperceptibility.
This thesis follows DSR methodology (Peffers et al. 2014; Hevner et al. 2004), guided by the three-cycle view (Hevner 2007):
Artifacts developed:
Start from common pipeline of adversarial attack on tabular data.
RQ1 build the foundation of imperceptibility on tabular data.
RQ2 benchmark the adversarial attacks under effectiveness and imperceptibility.
RQ3 design the new adversarial attack methods that unify effectiveness with tabular-specific imperceptibility.
Objective 1
🧩 Foundation of Imperceptibility on Tabular Data
Publication:
Zhipeng He, Chun Ouyang, Laith Alzubaidi, Alistair Barros, and Catarina Moreira. “Investigating imperceptibility of adversarial attacks on tabular data: An empirical analysis”. In: Intelligent Systems with Applications 25, 200461 (2025). DOI: 10.1016/j.iswa.2024.200461.





Three properties:


Objective 2
📊 Benchmark of Tabular Attacks
Paper:
Zhipeng He, Chun Ouyang, Lijie Wen, Cong Liu, and Catarina Moreira. “TabAttackBench: A benchmark for adversarial attacks on tabular data”. In: arXiv [cs.LG] (2025). arXiv: 2505.21027.
Submitted to Expert Systems with Applications, under \(1^{st}\) revision.

Select 10 datasets from tabular benchmarking suite (Gorishniy et al. 2021) under the following criteria:




Attack Success Rate (ASR):
\[ \text{ASR} = \frac{1}{n}\sum_{i=1}^{n}\one( \boldsymbol{x}^{adv}\neq y) \]
4 Quantitative Properties: Lower is better

Imperceptibility Score (IS): Equal-weighted harmonic mean of above normalised properties
\[ \text{IS} = \frac{4}{\frac{1}{\text{Proximity}} + \frac{1}{\text{Sparsity}} + \frac{1}{\text{Deviation}} + \frac{1}{\text{Sensitivity}}} \]
👉 Harmonic mean penalises imbalance (one bad metric drags IS down).



By using the two thresholds, we can divide the 2D density into four sectors.




💡 Insight 1: Propose based on unbounded attacks (C&W, DeepFool, etc.).
🧩 Insight 2: Consider the imperceptibility properties in the attack design.
⚙️ Insight 3: Unify both categorical and numerical feature spaces in attacks.
❓ Question: Can we incorporate the above insights to design a new attack for tabular data?
Objective 3
⚙️ Generative VAE-based Attack
Paper:
Zhipeng He, Alexander Stevens, Chun Ouyang, Johannes De Smedt, Alistair Barros, and Catarina Moreira. “Crafting imperceptible on-manifold adversarial attacks for tabular data”. In: arXiv [cs.LG] (2025). arXiv: 2507.10998.
Submitted to Applied Soft Computing, under \(1^{st}\) revision.
Manifold Hypothesis: High-dimensional data often lies on a lower-dimensional manifold embedded within the high-dimensional input space.
Unify both categorical and numerical feature spaces into a continuous latent space.
👉 Addressing the issue of categorical feature encoding.
Learn the distribution of original data to generate in-distribution adversarial examples.
👉 Addressing the deviation property of imperceptibility.
Step 1: VAE Training:
\[ \begin{align} \mathcal{L}_{\mathrm{VAE}} &= \underbrace{ \mathbb{E}_{q_\phi(z\mid x)} \Big[ \underbrace{\|x^{\mathrm{num}} - \hat{x}^{\mathrm{num}}\|^2}_{\substack{\text{Numerical reconstruction} \\ \text{(MSE, Gaussian likelihood)}}} + \underbrace{\mathcal{L}_{\mathrm{cat}}(x^{\mathrm{cat}}, \hat{x}^{\mathrm{cat}})}_{\substack{\text{Categorical reconstruction} \\ \text{(Cross-entropy, Softmax probability)}}} \Big] }_{\text{Reconstruction Loss}} \\ &\quad + \beta \cdot \underbrace{D_{\mathrm{KL}}\big(q_\phi(z\mid x) \parallel p(z)\big)}_{\substack{\text{KL divergence} \\ \text{(Latent regularisation)}}} \,+\, \alpha \cdot \underbrace{\mathcal{L}_{\text{cls}}(h_\omega(z), y)}_{\substack{\text{Classification loss} \\ \text{(Class separation)}}}. \end{align} \]

Step 2: Adversarial example generation:


Z-score normalisation to address the sensitivity property of imperceptibility.
Proposed In-Distribution Success Rate (IDSR) to measure the success rate of adversarial examples in the in-distribution, i.e., \(\mathrm{IDSR} = \mathrm{ASR} \times (1 - \mathrm{OR})\).
💡 Introducing the classification-aware loss (\(\mathcal{L}_{cls}\)) encourages the latent space to become more discriminative.


The VAE’s probabilistic latent structure better preserves both numerical continuity and categorical consistency than Generative Adversarial Network (GAN) (Goodfellow et al. 2014), making it more suitable for imperceptible adversarial example generation on tabular data.
💡 Our VAE-based attack achieves the best overall In-Distribution Success Rate (IDSR) while maintaining a low Outlier Rate (OR), outperforming other VAE-based methods.
💡 The latent space visualisations (t-SNE) show that adversarial examples (green) generated by our VAE-based attack remain closely aligned with original inputs (blue).



💡 Adversarial training effectively reduces Attack Success Rate (robustness gain) while maintaining relatively high model accuracy across all models.
🌟 Conclusion & Future Directions
Research Problem:
Approach: Three-part progression:
Outcome:
Conceptual
Analytical
Methodological
Practical
From theory to tools, the thesis bridges conceptual clarity → systematic evaluation → practical innovation.
Limitations
Future Work
Effort to “mend the fence before the sheep are lost”:
→ strengthening adversarial robustness for tabular data models.


Thank you!
Check out the slides here 👇
