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REVIEW 4 major objections 4 minor 21 references

Watermarking Kolmogorov-Arnold Networks for Emerging Networked Applications via Activation Perturbation

T0 review · 4 major / 4 minor · reviewed 2026-08-05 · deepseek-v4-flash

Pith's one-line read KAN models can be watermarked by perturbing layer-0 activations with a DCT signal, and the mark survives pruning and retraining.

desk verdict A plausible first KAN-specific watermarking method, but the central robustness claim is undercut by chance-level results on Fashion MNIST after pruning/retraining, and the method is not reproducible as written. read the letter →

arxiv 2508.06676 v1 pith:VGE3XSPI submitted 2025-08-08 cs.LG

classification cs.LG
keywords modelwatermarkingKolmogorov-ArnoldNetworksactivationperturbationdiscretecosinetransformintellectualpropertyprotectionfine-tuningattackpruningretrainingafter
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper tries to establish that a Kolmogorov-Arnold Network (KAN) can be watermarked by perturbing the outputs of its first learnable activation layer in the frequency domain, using the Discrete Cosine Transform. The proposed method, DCT-AW, is intended to be task-independent: it works for classification and regression because it does not rely on task-specific trigger samples or output labels. The paper further claims that this activation-level mark survives common removal attacks, including fine-tuning, pruning, and retraining after pruning, better than existing DNN watermarking methods transplanted onto KAN. If true, KAN model owners could verify ownership after an attacker has modified the model, with only a small measured change in the model's main-task performance.

What carries the argument

The load-bearing object is the perturbation rule $y' = \mathrm{IDCT}(\mathrm{DCT}(y) + P)$ applied to layer-0 activation outputs, where DCT is the Discrete Cosine Transform and $P$ is a fixed watermark signal in the frequency domain; this is what lets the mark be injected into learnable activation functions without task data. The second component is a three-layer MLP detector, trained on layer-0 activation outputs from watermarked and clean models with shuffling as augmentation, that classifies any suspect model's activations as watermarked or not. Layer 0 is chosen as the embedding site because earlier layers have weaker influence on the final output, so the perturbation preserves main-task

What would settle it

Train a KAN with DCT-AW, apply retrain-after-pruning, then run the trained detector on layer-0 activations from an unrelated KAN that was never watermarked and measure the false-positive rate; if the detector labels unrelated models as watermarked at rates near the reported attack-detection rates, the verification does not distinguish ownership. A second check is to replace the fixed perturbation $P$ with random frequency values and see whether the detection transfer remains, which would indicate the detector is keying on a generic artifact rather than the owner's specific signal.

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Extended reading notes

Core claim

The paper's central claim is that embedding a fixed frequency-domain perturbation into the layer-0 activation outputs of a KAN, via $y' = \mathrm{IDCT}(\mathrm{DCT}(y) + P)$, creates a detectable watermark that is independent of the downstream task and resistant to pruning-based removal. During training, the model first trains normally on its task and then updates the layer-0 activation parameters toward the perturbed outputs, so the signal becomes part of the learned activations rather than a separate trigger set. Verification is done with a small binary MLP detector trained only on activation outputs of the watermarked model versus a clean model, with shuffled variants as data augmentation

Load-bearing premise

The load-bearing premise is that a fixed perturbation $P$, which the paper never specifies, can be imposed on layer-0 activation outputs and then detected by a detector trained only on pristine clean versus watermarked activations, even after the suspect model has been pruned, fine-tuned, or retrained.

Editorial extensions

If this is right

  • If DCT-AW works as claimed, KAN-based models in networked applications can carry an ownership mark without needing task-specific trigger samples or label modifications.
  • A watermarked KAN would remain verifiable after an attacker fine-tunes it with a large learning rate, prunes 60% of parameters, or prunes and retrains, the three attacks in the paper's evaluation.
  • The same embedding procedure applies to regression tasks, where trigger-set and decision-boundary methods are hard to use, because the mark lives in activations rather than in output labels.
  • Because the watermark is embedded in layer-0 activation functions, it can be verified even when the model's downstream task head or output distribution changes, as long as the KAN layers are preserved.
  • The method's task independence would allow a single watermarking pipeline to protect KAN models across classification, regression, and future task types.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The paper does not report false-positive rates on unattacked or unrelated KANs, so an immediate follow-up is to measure whether the detector's transfer after attacks also flags models that were never watermarked.
  • Because the watermark signal $P$ is added to frequency components before the inverse transform, an attacker who knows the embedding rule could try to estimate or overwrite $P$ by re-training layer-0 activations toward clean-model behavior; testing this adversarial re-training would be a direct follow-up.
  • The same activation-perturbation idea could be tried on other architectures with learnable or differentiable activations, such as spline-based or piecewise-linear networks, to see whether task independence and pruning resistance carry over.
  • The paper leaves the choice and properties of $P$ unspecified; one testable design question is whether different owners can use different $P$ values to obtain unique, non-interchangeable watermarks while keeping the detector transfer.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 4 minor

Summary. The paper proposes DCT-AW, a watermarking scheme for Kolmogorov-Arnold Networks (KANs). The method embeds a watermark by perturbing layer-0 activation outputs in the discrete-cosine-transform (DCT) domain during training, and verifies ownership using a three-layer MLP detector trained to distinguish activation outputs of a watermarked KAN from those of an unwatermarked KAN. Experiments on MNIST, Fashion MNIST, and the Feynman regression benchmark compare DCT-AW against four DNN watermarking baselines, reporting watermark detection accuracy after fine-tuning, pruning, and retraining-after-pruning attacks. The central claims are that DCT-AW is task-independent, has small impact on model performance, and is robust to common watermark removal attacks.

Significance. If the claims hold, DCT-AW would be a useful first architecture-specific watermarking method for KANs, exploiting their learnable activation functions rather than transferring DNN weight-embedding or trigger-set methods. The paper also identifies a real gap: existing DNN watermarking techniques are not designed for KAN's pruning-sensitive architecture. However, the current evidence is insufficient to support the headline robustness claim. The watermark signal is never specified, detector transfer is not validated with false-positive controls, and one of the paper's own tables shows chance-level watermark accuracy after pruning attacks. These are fixable with additional specification and experiments, so the core idea is worth a major revision rather than rejection.

major comments (4)
  1. [§V-A, Eq. (5), Algorithm 1] The core perturbation signal P is never defined. Eq. (5) writes y' = IDCT(DCT(y) + P), but the paper does not state how P is generated, its length, its magnitude, its frequency support, or how it is derived from the watermark key w. Algorithm 1 line 9 is also notationally inconsistent: it writes Os = DCT(O, w), which does not match Eq. (5). Without a precise definition of P (or w), the method is not reproducible and the experiments cannot be independently reconstructed or assessed.
  2. [§V-B, Eqs. (6)-(7), Tables IV-VI] The detector is trained only on activation outputs from one clean KAN and one watermarked KAN before any attack. Robustness is then measured by applying this detector to attacked watermarked models. The paper reports no false-positive rates on attacked clean models, nor on independently trained unrelated KANs. Without such controls, high wm acc after pruning or retraining could simply reflect the detector labeling any out-of-distribution activation distribution as 'watermarked.' The authors should report FPR/ROC on attacked clean models and on independently trained KANs; this is essential for the verification claim.
  3. [Table V (Fashion MNIST), Pruning and Retrain after Pruning columns] The paper's abstract claims 'superior robustness against various watermark removal attacks, including pruning and retraining after pruning.' However, Table V shows DCT-AW wm acc = 50.01 after pruning and 50.15 after retraining after pruning on Fashion MNIST, i.e., chance level for binary classification. This directly contradicts the abstract and undermines the central robustness claim. The authors must either explain these results (e.g., different threshold, detector miscalibration) or qualify the claim. Single numbers without error bars or seed repetitions further weaken the comparison.
  4. [§VI-A, Tables IV-VI] The experimental protocol is under-specified. There are no details on detector architecture hyperparameters, training/validation split, number of runs, random seeds, or how the layer-0 activation outputs are pooled across samples. All tables report single point estimates, so statistical significance and run-to-run variability cannot be assessed. This is particularly important because robustness numbers in Tables IV-VI vary widely across datasets and attacks, and the baseline comparisons depend on exact percentages.
minor comments (4)
  1. [§III-B and §I] The phrase 'protecting in protecting deep neural networks' in the Introduction appears to be a typo; it should read 'protecting deep neural networks.'
  2. [§V-A, Table III] The choice of layer 0 as the embedding location is based on a single comparison per task using one classification and one regression dataset. This is a free parameter of the method, and the paper gives no sensitivity analysis across tasks, model sizes, or depths. A short ablation would strengthen the claim that layer 0 is generally preferable.
  3. [Title, Abstract, §VI] The title and abstract mention 'Emerging Networked Applications,' but the experiments include only standard image classification (MNIST, Fashion MNIST) and textbook equation regression (Feynman). No network-structured data or social-network-type task is evaluated, so the 'networked applications' framing is not supported by the reported evidence.
  4. [Algorithm 1] Algorithm 1 does not define the 'signal loss' weight relative to the main-task loss, nor how the two training phases are balanced. The paper should specify the exact objective optimized in Step 2 and the learning rates/epoch counts used for embedding.

Circularity Check

1 steps flagged · score 4.0 of 10

Initial wm acc is a supervised-fit metric; robustness is uncalibrated and partly fails, but functionality/task-independence results remain independent.

  1. fitted input called prediction [Section V-B, Eqs. (6)-(7); Section VI-A 'watermark accuracy' definition]
    "Label(od_n) = {1 if n = wm or n = wm′, 0 if n = m or n = m′. (6) ... LDetect = CrossEntropy(Md(Xd), Yd). (7) ... We calculate the watermark detection rate as the number of testing instances successfully detected by the detector to the total number of testing instances."

    The detector Md is trained specifically to separate layer-0 activations of the watermarked model Mwm from those of the clean model Mm (Eqs. 6-7). The paper's only watermark metric, wm acc, is this detector's classification accuracy on held-out activations from those same two models. Thus the reported 100% initial wm acc measures supervised separability of the two training distributions, not the presence of an independently specified perturbation P (which is never defined in the paper). The only independent transfer test is robustness after attacks, but that test is uncalibrated: no false-positive rate on attacked clean models is reported, and Table V shows chance-level wm acc (50.01/50.15) after pruning/retraining on Fashion MNIST, contradicting the claimed robustness. The verification cla

full rationale

The paper's core embedding procedure (Eq. 5 and Algorithm 1) is an explicit activation-perturbation scheme, and the functionality-preservation and task-independence results are evaluated on standard external benchmarks (MNIST, Fashion MNIST, Feynman) against independent baselines, so those parts are not circular. The preliminary weakness analysis is original experimentation, not a citation-dependent premise. The only self-citation of note is USP [3], a prior work by co-author Chih-Ya Shen, used as a baseline; it is not load-bearing for the proposed method's validity. However, the watermark-verification metric is partially circular: the detector is fit to exactly the two classes it later 'detects,' so high initial wm acc is a supervised-fit result rather than an independent watermark-key verification. The robustness claim depends on detector transfer to attacked models, which is neither calibrated by false-positive checks on attacked clean models nor consistently achieved, as the Fashion MNIST results show. These are genuine circularity/validation concerns, but they do not make the whole derivation equivalent to its inputs, hence a moderate score of 4.

Assumptions & free parameters 3 free parameters · 4 assumptions · 0 invented entities

The central claim rests on unspecified practical components, mainly the perturbation signal P, the layer choice, and detector training. No new physical or mathematical entities are introduced.

free parameters (3)
  • Perturbation signal P = not specified
    The core embedded signal in Equation (5); no generation rule, amplitude, frequency band, or random seed is given.
  • Embedding layer index = 0
    Layer 0 is chosen from Table III comparing layer 0 versus layer 1 on one classification and one regression task, with no detection accuracy or variance reported for the choice.
  • Detector hyperparameters = not specified
    A three-layer MLP detector is described, but hidden sizes, epochs, learning rate, batch size, and train/test split are absent.
assumptions (4)
  • standard math The Kolmogorov-Arnold representation theorem justifies the KAN architecture with learnable univariate activations.
    Invoked in Section III-A as the theoretical basis for KAN.
  • standard math The DCT and IDCT pair is invertible and preserves the representable signal shape.
    Used in Section V-A to define the perturbation operation in the frequency domain.
  • domain assumption Layer-0 activation outputs are observable and stable enough to carry an embedded signal across training and attacks.
    The entire embedding and verification pipeline in Sections V-A and V-B depends on this assumption, but no analysis supports it.
  • domain assumption An attacker does not know the perturbation signal or the detector, so verification remains meaningful.
    The threat model in Sections II and V-B implicitly assumes the watermark secret is not available to the attacker.

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Cite this review

Pith. "Pith review of Watermarking Kolmogorov-Arnold Networks for Emerging Networked Applications via Activation Perturbation." pith.science (2026). https://pith.science/paper/VGE3XSPI

@misc{pith2026250806676,
  author       = {Pith},
  title        = {Pith review of: Watermarking Kolmogorov-Arnold Networks for Emerging Networked Applications via Activation Perturbation},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/VGE3XSPI}},
  note         = {Machine review of arXiv:2508.06676}
}
read the original abstract

With the increasing importance of protecting intellectual property in machine learning, watermarking techniques have gained significant attention. As advanced models are increasingly deployed in domains such as social network analysis, the need for robust model protection becomes even more critical. While existing watermarking methods have demonstrated effectiveness for conventional deep neural networks, they often fail to adapt to the novel architecture, Kolmogorov-Arnold Networks (KAN), which feature learnable activation functions. KAN holds strong potential for modeling complex relationships in network-structured data. However, their unique design also introduces new challenges for watermarking. Therefore, we propose a novel watermarking method, Discrete Cosine Transform-based Activation Watermarking (DCT-AW), tailored for KAN. Leveraging the learnable activation functions of KAN, our method embeds watermarks by perturbing activation outputs using discrete cosine transform, ensuring compatibility with diverse tasks and achieving task independence. Experimental results demonstrate that DCT-AW has a small impact on model performance and provides superior robustness against various watermark removal attacks, including fine-tuning, pruning, and retraining after pruning.

Figures

Figures reproduced from arXiv: 2508.06676 by the authors.

Figure 1
Figure 1. Illustration of watermark embedding and verification process. In the [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Concept of the proposed approach DCT-AW [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗

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Reference graph

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