Privacy Preserving Anomaly Detection on Homomorphic Encrypted Data from IoT Sensors
Pith reviewed 2026-05-24 02:39 UTC · model grok-4.3
The pith
A histogram anomaly detector identifies faults in IoT sensor data while the readings stay encrypted under TFHE.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The authors adapt the histogram-based outlier detection technique to the TFHE homomorphic encryption scheme by creating vectorized support operations for addition, bucket placement, frequency labeling of abnormal buckets, and range labeling of abnormal values. These operations fit within TFHE's constraints on input size and circuit depth. Evaluation on IoT-like data shows the encrypted detector identifies the same anomalies as the plaintext version while keeping all data encrypted.
What carries the argument
Vectorized support operations (addition, bucket placement, frequency labeling, range labeling) implemented inside TFHE to enable histogram anomaly detection on ciphertexts.
If this is right
- Anomaly detection can be performed on encrypted IoT streams without exposing raw sensor values.
- The detector continues to work correctly under noisy data, communication failures, and device malfunctions.
- The same vectorized operations support labeling of both abnormal buckets and individual abnormal values.
- Computational cost rises but stays within ranges reported for other TFHE applications.
Where Pith is reading between the lines
- The vectorization pattern used here could be applied to other lightweight statistical checks on encrypted IoT streams.
- If the operations remain stable at larger data volumes, the method could support continuous monitoring without periodic decryption.
- Replacing the histogram step with a different threshold rule would still rely on the same TFHE vector primitives.
Load-bearing premise
The vectorized support operations can be realized inside TFHE without introducing errors that alter the final anomaly decisions compared to plaintext processing.
What would settle it
Run the encrypted detector and the plaintext detector on identical IoT sensor datasets and check whether the sets of flagged anomalous values are exactly the same.
Figures
read the original abstract
IoT devices have become indispensable components of our lives, and the advancement of AI technologies will make them even more pervasive, increasing the vulnerability to malfunctions or cyberattacks and raising privacy concerns. Encryption can mitigate these challenges; however, most existing anomaly detection techniques decrypt the data to perform the analysis, potentially undermining the encryption protection provided during transit or storage. Homomorphic encryption schemes are promising solutions as they enable the processing and execution of operations on IoT data while still encrypted, however, these schemes offer only limited operations, which poses challenges to their practical usage. In this paper, we propose a novel privacy-preserving anomaly detection solution designed for homomorphically encrypted data generated by IoT devices that efficiently detects abnormal values without performing decryption. We have adapted the Histogram-based anomaly detection technique for TFHE scheme to address limitations related to the input size and the depth of computation by implementing vectorized support operations. These operations include addition, value placement in buckets, labeling abnormal buckets based on a threshold frequency, labeling abnormal values based on their range, and bucket labels. Evaluation results show that the solution effectively detects anomalies without requiring data decryption and achieves consistent results comparable to the mechanism operating on plain data. Also, it shows robustness and resilience against various challenges commonly encountered in IoT environments, such as noisy sensor data, adversarial attacks, communication failures, and device malfunctions. Moreover, the time and computational overheads determined for several solution configurations, despite being large, are reasonable compared to those reported in existing literature.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes adapting a histogram-based anomaly detection algorithm to the TFHE homomorphic encryption scheme for IoT sensor data. It implements vectorized encrypted operations for addition, bucket placement, frequency-based abnormal bucket labeling, range-based abnormal value labeling, and bucket labeling. The central claim is that these operations enable anomaly detection on encrypted data without decryption while producing results comparable to the plaintext version, with additional claims of robustness to noise, attacks, failures, and malfunctions, and reasonable overhead relative to prior work.
Significance. If the homomorphic realizations of bucket placement and labeling are shown to produce anomaly decisions identical to plaintext (i.e., zero decision-bit errors on the evaluated traces), the work would supply a concrete, operation-limited example of privacy-preserving statistical anomaly detection suitable for constrained IoT settings. The explicit vectorization to fit TFHE's supported gates is a constructive step, though the absence of noise-budget verification weakens the empirical support for the comparability claim.
major comments (3)
- [Evaluation section] Evaluation section: the manuscript states that results are 'consistent' and 'comparable' to plaintext processing but reports no quantitative agreement metrics (e.g., fraction of identical anomaly decisions, precision/recall deltas, or per-trace decision error rates) between the TFHE and plaintext runs. This metric is required to substantiate the central claim that the encrypted detector 'effectively detects anomalies without requiring data decryption.'
- [Implementation / Evaluation] No circuit-depth or noise analysis is provided for the vectorized support operations (bucket placement, frequency labeling, range labeling). TFHE noise grows with each addition and comparison; without parameter selection, bootstrapping schedule, or verification that all intermediate ciphertexts remain below the decryption threshold on the sensor traces, it is impossible to confirm that the homomorphic decisions match the plaintext histogram decisions exactly.
- [Evaluation section] The robustness claims (noisy sensor data, adversarial attacks, communication failures) are asserted in the abstract and evaluation summary, yet the text does not describe how these perturbations were injected into the encrypted traces or quantify their effect on the encrypted detector's output relative to plaintext.
minor comments (2)
- [Abstract] The abstract refers to 'several solution configurations' and 'reasonable' overheads without defining the configurations (bucket count, threshold values) or providing the concrete timing numbers.
- [Method] Notation for the vectorized operations (e.g., how bucket indices and frequency counters are encoded as TFHE ciphertexts) is introduced but not formalized with pseudocode or circuit diagrams.
Simulated Author's Rebuttal
We thank the referee for the constructive and detailed comments. We address each major comment below and will revise the manuscript accordingly to strengthen the evaluation and implementation sections.
read point-by-point responses
-
Referee: [Evaluation section] Evaluation section: the manuscript states that results are 'consistent' and 'comparable' to plaintext processing but reports no quantitative agreement metrics (e.g., fraction of identical anomaly decisions, precision/recall deltas, or per-trace decision error rates) between the TFHE and plaintext runs. This metric is required to substantiate the central claim that the encrypted detector 'effectively detects anomalies without requiring data decryption.'
Authors: We agree that quantitative metrics are needed to substantiate the comparability claim. In the revised manuscript we will report the fraction of identical anomaly decisions, decision error rates, and any precision/recall differences between the TFHE and plaintext runs on the evaluated traces. revision: yes
-
Referee: [Implementation / Evaluation] No circuit-depth or noise analysis is provided for the vectorized support operations (bucket placement, frequency labeling, range labeling). TFHE noise grows with each addition and comparison; without parameter selection, bootstrapping schedule, or verification that all intermediate ciphertexts remain below the decryption threshold on the sensor traces, it is impossible to confirm that the homomorphic decisions match the plaintext histogram decisions exactly.
Authors: We will add a dedicated subsection on circuit depth and noise analysis, including the TFHE parameter set, bootstrapping schedule, and explicit verification that noise remains below the decryption threshold for all operations on the sensor traces. revision: yes
-
Referee: [Evaluation section] The robustness claims (noisy sensor data, adversarial attacks, communication failures) are asserted in the abstract and evaluation summary, yet the text does not describe how these perturbations were injected into the encrypted traces or quantify their effect on the encrypted detector's output relative to plaintext.
Authors: We will revise the evaluation section to describe the exact injection methods for each perturbation type and to report quantitative effects on the encrypted detector's outputs relative to the plaintext baseline. revision: yes
Circularity Check
No significant circularity; empirical comparison is self-contained
full rationale
The paper adapts a standard histogram anomaly detection method to TFHE via vectorized operations and reports empirical results showing comparable anomaly decisions on encrypted vs. plaintext IoT sensor data. No equations, parameters, or claims reduce the reported detection performance to a fitted constant, self-citation chain, or definition internal to the paper. The central result rests on direct experimental runs against external sensor traces rather than any construction that forces equivalence by design.
Axiom & Free-Parameter Ledger
free parameters (1)
- threshold frequency for abnormal bucket labeling
axioms (1)
- domain assumption TFHE supports addition, comparison, and limited-depth circuits sufficient for the vectorized bucket and labeling steps
Reference graph
Works this paper leans on
-
[1]
Chatterjee, A., & Ahmed, B. S. (2022). IoT anomaly detection methods and applications: A survey. Internet of Things, 19, 100568
work page 2022
-
[2]
Blázquez-García, A., Conde, A., Mori, U., & Lozano, J. A. (2021). A review on outlier/anomaly detection in time series data. ACM Computing Surveys (CSUR), 54(3), 1-33
work page 2021
-
[3]
Zhang, C., Yin, A., Zuo, W., & Chen, Y . (2020). Privacy preserving anomaly detection based on local density estimation. Mathematical Biosciences and Engineering, 17(4), 3478-3497
work page 2020
-
[4]
Alabdulatif, A., Kumarage, H., Khalil, I., & Yi, X. (2017). Privacy-preserving anomaly detection in cloud with lightweight homomorphic encryption. Journal of Computer and System Sciences, 90, 28-45
work page 2017
-
[5]
Alabdulatif, A., Khalil, I., Kumarage, H., Zomaya, A. Y ., & Yi, X. (2019). Privacy-preserving anomaly detection in the cloud for quality assured decision-making in smart cities. Journal of Parallel and Distributed Computing, 127, 209-223
work page 2019
-
[6]
Chen, S., Susilo, W., Zhang, Y ., Yang, B., & Zhang, M. (2023). Privacy-preserving anomaly counting for time-series data in edge-assisted crowdsensing. Computer Standards & Interfaces, 85, 103707
work page 2023
-
[7]
Song, Y ., Wei, F., Zhu, K., & Zhu, Y . (2022). Anomaly Detection as a Service: An Outsourced Anomaly Detection Scheme for Blockchain in a Privacy-Preserving Manner. IEEE Transactions on Network and Service Management, 19(4), 3794-3809
work page 2022
-
[8]
Lai, S., Yuan, X., Sakzad, A., Salehi, M., Liu, J. K., & Liu, D. (2019). Enabling efficient privacy-assured outlier detection over encrypted incremental data sets. IEEE Internet of Things Journal, 7(4), 2651- 2662
work page 2019
-
[9]
Wen, M., Xie, R., Lu, K., Wang, L., & Zhang, K. (2021). Feddetect: A novel privacy-preserving federated learning framework for energy theft detection in smart grid. IEEE Internet of Things Journal, 9(8), 6069-6080
work page 2021
-
[10]
Li, R., Ishimaki, Y ., & Yamana, H. (2019, June). Fully homomorphic encryption with table lookup for privacy-preserving smart grid. In 2019 IEEE International Conference on Smart Computing (SMARTCOMP) (pp. 19-24). IEEE
work page 2019
-
[11]
Li, R., Bhattacharjee, S., Das, S. K., & Yamana, H. (2022, June). Look-Up Table based FHE System for Privacy Preserving Anomaly Detection in Smart Grids. In 2022 IEEE International Conference on Smart Computing (SMARTCOMP) (pp. 108-115). IEEE
work page 2022
-
[12]
Itokazu, K., Wang, L., & Ozawa, S. (2021, July). Outlier Detection by Privacy-Preserving Ensemble Decision Tree U sing Homomorphic Encryption. In 2021 International Joint Conference on Neural Networks (IJCNN) (pp. 1-7). IEEE
work page 2021
-
[13]
Mehnaz, S., & Bertino, E. (2020, April). Privacy-preserving real-time anomaly detection using edge computing. In 2020 IEEE 36th International Conference on Data Engineering (ICDE) (pp. 469-480). IEEE
work page 2020
-
[14]
Shen, M., Tang, X., Zhu, L., Du, X., & Guizani, M. (2019). Privacy-preserving support vector machine training over blockchain-based encrypted IoT data in smart cities. IEEE Internet of Things Journal, 6(5), 7702-7712
work page 2019
-
[15]
Alexandru, A. B., Burbano, L., Çeliktuğ, M. F., Gomez, J., Cardenas, A. A., Kantarcioglu, M., & Katz, J. (2022, December). Private Anomaly Detection in Linear Controllers: Garbled Circuits vs. Homomorphic Encryption. In 2022 IEEE 61st Conference on Decision and Control (CDC) (pp. 7746- 7753). IEEE
work page 2022
-
[16]
Cui, L., Qu, Y ., Xie, G., Zeng, D., Li, R., Shen, S., & Yu, S. (2021). Security and privacy-enhanced federated learning for anomaly detection in IoT infrastructures. IEEE Transactions on Industrial Informatics, 18(5), 3492-3500
work page 2021
-
[17]
L., Bernal-Bernabe, J., & Skarmeta, A
Ruzafa-Alcázar, P ., Fernández-Saura, P ., Mármol-Campos, E., González-Vidal, A., Hernández-Ramos, J. L., Bernal-Bernabe, J., & Skarmeta, A. F. (2021). Intrusion detection based on privacy-preserving federated learning for the industrial IoT. IEEE Transactions on Industrial Informatics, 19(2), 1145- 1154
work page 2021
-
[18]
Truex, S., Liu, L., Chow, K. H., Gursoy, M. E., & Wei, W. (2020, April). LDP-Fed: Federated learning with local differential privacy. In Proceedings of the Third ACM International Workshop on Edge Systems, Analytics and Networking (pp. 61-66)
work page 2020
-
[19]
Liu, Y ., Garg, S., Nie, J., Zhang, Y ., Xiong, Z., Kang, J., & Hossain, M. S. (2020). Deep anomaly detection for time-series data in industrial IoT: A communication-efficient on-device federated learning approach. IEEE Internet of Things Journal, 8(8), 6348-6358
work page 2020
-
[20]
Arazzi, M., Nicolazzo, S., & Nocera, A. (2023). A Fully Privacy -Preserving Solution for Anomaly Detection in IoT using Federated Learning and Homomorphic Encryption. Information Systems Frontiers, 1-24
work page 2023
-
[21]
Concrete, What is Concrete?, https://docs.zama.ai/concrete/, [accessed February, 2024]
work page 2024
-
[22]
2021 electricity and heat demand data for a city district (Belgium)
De Mulder, C., “2021 electricity and heat demand data for a city district (Belgium)”. Zenodo, Jan. 20,
work page 2021
-
[23]
doi: 10.5281/zenodo.5155659
-
[24]
Concrete, Depth and complexity of circuit , https://community.zama.ai/t/depth-and-complexity-of- circuit/485 [accessed February, 2024]
work page 2024
-
[25]
Diraco, G.; Rescio, G.; Caroppo, A.; Manni, A.; Leone, A. Human Action Recognition in Smart Living Services and Applications: Context Awareness, Data Availability, Personalization, and Privacy. Sensors 2023, 23, 6040. https://doi.org/10.3390/s23136040
-
[26]
Farrokhi, A., Farahbakhsh, R., Rezazadeh, J., & Minerva, R. (2021). Application of Internet of Things and artificial intelligence for smart fitness: A survey. Computer Networks, 189, 107859
work page 2021
-
[27]
Soori, M., Arezoo, B., & Dastres, R. (2023). Internet of things for smart factories in industry 4.0, a review. Internet of Things and Cyber-Physical Systems
work page 2023
-
[28]
Ahmad, T., Zhu, H., Zhang, D., Tariq, R., Bassam, A., Ullah, F., ... & Alshamrani, S. S. (2022). Energetics Systems and artificial intelligence: Applications of industry 4.0. Energy Reports, 8, 334-361
work page 2022
-
[29]
Villegas-Ch, W., Govea, J., & Jaramillo-Alcazar, A. (2023). IoT Anomaly Detection to Strengthen Cybersecurity in the Critical Infrastructure of Smart Cities. Applied Sciences, 13(19), 10977
work page 2023
-
[30]
V., Anwar, A., Nasirian, A., & Olani, G
Diro, A., Kaisar, S., Vasilakos, A. V., Anwar, A., Nasirian, A., & Olani, G. (2024). Anomaly detection for space information networks: A survey of challenges, techniques, and future directions. Computers & Security, 139, 103705
work page 2024
-
[31]
Li, C., Wang, J., Wang, S., & Zhang, Y . (2023). A review of IoT applications in healthcare. Neurocomputing, 127017
work page 2023
-
[32]
H., Lu, R., Xiong, P ., & Iqbal, S
Sasi, T., Lashkari, A. H., Lu, R., Xiong, P ., & Iqbal, S. (2023). A Comprehensive Survey on IoT Attacks: Taxonomy, Detection Mechanisms and Challenges. Journal of Information and Intelligence
work page 2023
-
[33]
Bourse, F., Sanders, O., & Traoré, J. (2020, February). Improved secure integer comparison via homomorphic encryption. In Cryptographers’ Track at the RSA Conference (pp. 391 -416). Cham: Springer International Publishing
work page 2020
-
[34]
Babenko, M., & Golimblevskaia, E. (2021, January). Euclidean division method for the homomorphic scheme ckks. In 2021 IEEE Conference of Russian Young Researchers in Electrical and Electronic Engineering (ElConRus) (pp. 217-220). IEEE
work page 2021
-
[35]
Shrestha, R., & Kim, S. (2019). Integration of IoT with blockchain and homomorphic encryption: Challenging issues and opportunities. In Advances in computers (Vol. 115, pp. 293-331). Elsevier
work page 2019
-
[36]
Zhang, L., Li, C., Hu, Q., Lang, J., Huang, S., Hu, L., ... & Lv, C. (2023). Enhancing Privacy in Large Language Model with Homomorphic Encryption and Sparse Attention. Applied Sciences, 13(24), 13146
work page 2023
-
[37]
Craig, G., A fully homomorphic encryption scheme. Diss. Stanford University, 2009
work page 2009
-
[38]
Concrete, Basics of FHE programs , https://docs.zama.ai/concrete/getting-started/fhe_basics, [accessed February, 2024]
work page 2024
-
[39]
Ames, S., Venkitasubramaniam, M., Page, A., Kocabas, O., & Soyata, T. (2015). Secure health monitoring in the cloud using homomorphic encryption: A branching -program formulation. In Enabling Real-Time Mobile Cloud Computing through Emerging Technologies (pp. 116-152). IGI Global
work page 2015
-
[40]
Microsoft SEAL, https://github.com/microsoft/SEAL?tab=readme-ov-file, [accessed February, 2024]
work page 2024
-
[41]
Chillotti, I., Gama, N., Georgieva, M., & Izabachène, M. (2020). TFHE: fast fully homomorphic encryption over the torus. Journal of Cryptology, 33(1), 34-91
work page 2020
-
[42]
Brakerski, Z., Gentry, C., & Vaikuntanathan, V. (2014). (Leveled) fully homomorphic encryption without bootstrapping. ACM Transactions on Computation Theory (TOCT), 6(3), 1-36
work page 2014
-
[43]
H., Kim, A., Kim, M., & Song, Y
Cheon, J. H., Kim, A., Kim, M., & Song, Y . (2017). Homomorphic encryption for arithmetic of approximate numbers. In Advances in Cryptology–ASIACRYPT 2017: 23rd International Conference on the Theory and Applications of Cryptology and Information Security, Hong Kong, China, December 3- 7, 2017, Proceedings, Part I 23 (pp. 409-437). Springer International ...
work page 2017
-
[44]
Fan, J., & Vercauteren, F. (2012). Somewhat practical fully homomorphic encryption. Cryptology ePrint Archive
work page 2012
-
[45]
Concrete, Composition, https://docs.zama.ai/concrete/tutorials/composition, [accessed February, 2024]
work page 2024
-
[46]
Concrete, Floating Points, https://docs.zama.ai/concrete/tutorials/floating_points, [accessed February, 2024]
work page 2024
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.