I'm a researcher studying the security of machine learning and the machine learning of security. My goal is to better understand machine learning and intelligent systems, in order to improve their safety and broaden their utility. I mainly have expertise in machine learning and deep learning, cyber security and trust, and secure systems and protocols.
Publications
- C. Lewis, V. Varadharajan, N. Noman, U. Tupakula, and K. K. Karmakar, "Achieving robustness and dropout fairness with hierarchical federated learning in smart grid infrastructures," ACM Transactions on Cyber-Physical Systems, vol. 9, no. 4, 2025, issn: 2378-962X. doi: 10.1145/3771547. [pdf] [code]
- C. Wang, J. Xu, J. Chen, V. Varadharajan, and C. Lewis, "PrivESD: A Privacy-Preserving Cloud-Edge Collaborative Logistic Regression Model over Encrypted Streaming Data," in IEEE Transactions on Dependable and Secure Computing, doi: 10.1109/TDSC.2025.3617797. [pdf]
- C. Lewis, V. Varadharajan, N. Noman, U. Tupakula, and N. Li, "Mitigation of gradient inversion attacks in federated learning with private adaptive optimization," in IEEE 44th International Conference on Distributed Computing Systems (ICDCS), 2024, pp. 833–845. doi: 10.1109/ICDCS60910.2024.00082. [pdf] [code]
- C. Lewis, V. Varadharajan, N. Noman, and U. Tupakula, "Ensuring fairness and gradient privacy in personalized heterogeneous federated learning," ACM Transactions on Intelligent Systems and Technology, vol. 15, no. 3, 2024, issn: 2157-6904. doi: 10.1145/3652613. [pdf] [code]
- C. Lewis, V. Varadharajan, and N. Noman, "Attacks against federated learning defense systems and their mitigation," Journal of Machine Learning Research, vol. 24, no. 30, pp. 1–50, 2023. [pdf] [code]
- C. Lewis, N. Li, and V. Varadharajan, "Targeted context based attacks on trust management systems in IoT," IEEE Internet of Things Journal, vol. 10, no. 14, pp. 12 186–12 203, 2023. doi: 10.1109/JIOT.2023.3245605. [pdf] [code]
Teaching
Goethe Universität Frankfurt am Main, Germany
- Seminar: The Security of Machine Learning – Creation, Co-ordination, Teaching, and Marking – 2026
The University of Newcastle, Australia
- Cloud Computing – Marking – 2025
- Network and Distributed Computing – Teaching Assistance and Marking – 2023
- Engineering Statistics – Teaching Assistance and Marking – 2023
- Data Wrangling and Visualisation – Teaching Assistance, Marking, and Course Content Development – 2023-2024
- Data Security – Teaching Assistance and Marking – 2023-2024
- Advanced Database – Teaching Assistance and Marking – 2021-2023
- Programming Languages and Paradigms – Teaching Assistance – 2022
- Introduction to Object Oriented Programming – Teaching Assistance and Marking, 2020-2023
- System and Network Security – Teaching Assistance and Marking – 2019-2024
- Data Security – Course Content Development – 2019