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Niklas Medinger

Ph.D. Student
CISPA – Helmholtz Center for Information
nik (dot) medinger (at) gmail (dot) com


About Me

I am a Ph.D. student at Saarbrücken Graduate School of Computer Science supervised by Prof. Dr. Cas Cremers at CISPA Helmholtz Center for Information Security. Before starting my Ph.D., I finished a Bachelor’s degree in Cybersecurity at Saarland University under Prof. Dr. Cas Cremers and Dr. Robert Künnemann. I expect to submit my dissertation in November 2026.

Together with Matthias Cosler, Cas Cremers, Bernd Finkbeiner, and Mohamed Ghanem, I have developed a reinforcement learning framework for the Tamarin Prover. Inspired by AlphaZero and AlphaProof, it guides Tamarin’s proof search with a learned neural heuristic, solving more lemmas with shorter proofs than Tamarin’s built-in heuristics. This work will appear at ACM CCS 2026.

Together with Aurora Naska and Cas Cremers, I have formally proven that modern messaging apps like Signal, iMessage, and WhatsApp cannot achieve full post-compromise security for end-users while being resistant against state loss that is caused by, for instance, an end-user losing their device.

Together with Alexander Dax and Cas Cremers, I have proposed novel security notions for key encapsulation mechanisms (KEMs) in the computational model of cryptography, created new, more realistic models for KEMs in the symbolic model of cryptography, and introduced a methodology to analyze protocols that use KEMs using the Tamarin Prover. This work received the 2025 Cybersecurity Award for the Best Theoretical Research Paper.

From August to November 2023, I have worked as an Applied Science Intern in the Automated Reasoning Group at Amazon Web Services, Santa Clara. There, I was supervised by Dimitra Giannakopoulou, Zvonimir Rakamaric, and Niloofar Razavi.

Together with Benjamin Kiesl-Reiter and Cas Cremers, I have created and proven secure an extensive formal model of IEEE’s 802.11 WPA2 protocol.

Research Interests

Publications

  1. ACM CCS 2026
    Less Effort, Shorter Proofs: Reinforcement Learning for Security Protocol Analysis in Tamarin
    Matthias Cosler, Cas Cremers, Bernd Finkbeiner, Mohamed Ghanem, and Niklas Medinger
    ACM Conference on Computer and Communications Security, 2026 (to appear).
    PDF Code BibTex

  2. S&P 2025
    Impossibility Results for Post-Compromise Security in Real-World Communication Systems
    Cas Cremers, Niklas Medinger, and Aurora Naska
    IEEE Symposium on Security and Privacy 2025
    PDF Code BibTex

  3. ACM CCS 2024
    Keeping Up with the KEMs: Stronger Security Notions for KEMs and automated analysis of KEM-based protocols
    Cas Cremers, Alexander Dax, and Niklas Medinger
    ACM Conference on Computer and Communications Security, 2024.
    PDF Code BibTex
    Distinguished Artifact Award, Cybersecurity Award 2025 (Best Theoretical Research Paper)

  4. USENIX Security 2020
    A Formal Analysis of IEEE 802.11's WPA2: Countering the Kracks Caused by Cracking the Counters
    Cas Cremers, Benjamin Kiesl-Reiter, and Niklas Medinger
    29th USENIX Security Symposium, 2020.
    PDF Code BibTex

Teaching