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My Research

I am currently a CNRS postdoctoral researcher at the Institut de Recherche en Informatique Fondamentale (IRIF) of Université Paris Cité, in the team of Geoffroy Couteau. Previously, I was pre- and postdoctoral researcher at the Karlsruhe Institute of Technology (KIT).

My general research interests are Digital Signatures, Lattice-Based Cryptography, Private Stream Aggregation and Privacy Notions, Hardware Assumptions in Cryptography, Card-Based Cryptography, Universal Composability, Algebraic Geometric Codes, Privacy-Preserving Contact Tracing and Statistics.

My current research focus is on Secure Multiparty Computation with Low Interaction from Pseudorandom Correlation Functions (PCFs), Post-Quantum Cryptography, Improving Science with Cryptography, Privacy-Enhancing Technologies, Secure Multiparty Computation for the Social Good.

The title of my dissertation is Cryptographic Protocols from Physical Assumptions.

Publications

See also my pages at DBLP, ORCID, Google Scholar.

Peer-Reviewed Conference Papers

  1. Geoffroy Couteau, Lalita Devadas, Srinivas Devadas, Alexander Koch, and Sacha Servan-Schreiber. QuietOT: Lightweight Oblivious Transfer with a Public-Key Setup. Accepted at: ASIACRYPT 2024. [Full version].
  2. Johannes Ottenhues and Alexander Koch. LaPSuS – A Lattice-Based Private Stream Aggregation Scheme under Scrutiny. In: SCN 2024. Ed. by Clemente Galdi and Duong Hieu Phan. LNCS 14974. Springer, 2024. pp. 228 – 248. [Full version], [Slides]
  3. Robin Berger, Felix Dörre and Alexander Koch. Two-Party Decision Tree Training from Updatable Order-Revealing Encryption. In: ACNS 2024, Proceedings. Ed. by Lejla Batina and Christina Pöpper. LNCS 14583. Springer, 2024. pp. 288–317. [Submission version], [Slides by R. Berger]
  4. Samuel Hand, Alexander Koch, Pascal Lafourcade, Daiki Miyahara and Léo Robert. Check Alternating Patterns: A Physical Zero-Knowledge Proof for Moon-or-Sun. In: International Workshop on Security, IWSEC 2023. Ed. by Junji Shikata and Hiroki Kuzuno. LNCS 14128. Springer, 2023. pp. 255–272. [ePrint version]
  5. Sebastian Faller, Pascal Baumer, Michael Klooß, Alexander Koch, Astrid Ottenhues and Markus Raiber. Black-Box Accumulation Based on Lattices. In: IMA International Conference on Cryptography and Coding, IMACC 2021. Ed. by M. B. Paterson. LNCS 13129. Springer, 2021. pp. 220–246. [Full version], [Slides by S. Faller].
  6. Wasilij Beskorovajnov, Felix Dörre, Gunnar Hartung, Alexander Koch, Jörn Müller-Quade and Thorsten Strufe. ConTra Corona: Contact Tracing against the Coronavirus by Bridging the Centralized–Decentralized Divide for Stronger Privacy. In: ASIACRYPT 2021, Proceedings. Ed. by Mehdi Tibouchi and Huaxiong Wang. LNCS 13091. Springer, 2021. pp. 665–695. [Full version], [Slides].
  7. Alexander Koch and Stefan Walzer. Foundations for Actively Secure Card-based Cryptography. In: Fun with Algorithms, FUN 2021. Ed. by Martin Farach-Colton, Giuseppe Prencipe, and Ryuhei Uehara. Vol. 157. LIPIcs. Schloss Dagstuhl – Leibniz-Zentrum für Informatik, 2020, 17:1–17:23. [ePrint version], [Slides]
  8. Alexander Koch, Michael Schrempp, and Michael Kirsten. Card-based Cryptography Meets Formal Verification. In: ASIACRYPT 2019, Proceedings. Ed. by Steven Galbraith and Shiho Moriai. LNCS 11921. Springer, 2019. pp. 488–517. [Full version], [Slides]
  9. Dirk Achenbach, Roland Gröll, Timon Hackenjos, Alexander Koch, Bernhard Löwe, Jeremias Mechler, Jörn Müller-Quade and Jochen Rill. Your Money or Your Life—Modeling and Analyzing the Security of Electronic Payment in the UC Framework. In: Financial Cryptography and Data Security 2019, Revised Selected Papers. Ed. by Ian Goldberg and Tyler Moore. LNCS 11598. Springer, 2019. pp. 243–261. [IFCA version]
  10. Julia Kastner, Alexander Koch, Stefan Walzer, Daiki Miyahara, Yu-ichi Hayashi, Takaaki Mizuki, and Hideaki Sone. The Minimum Number of Cards in Practical Card-based Protocols. In: ASIACRYPT 2017, Proceedings. Ed. by Takagi Tsuyoshi and Thomas Peyrin. LNCS 10626. Springer, 2017, pp. 126–155. [Full version], [Slides, Copy part by D. Miyahara]
  11. Gunnar Hartung, Björn Kaidel, Alexander Koch, Jessica Koch, and Dominik Hartmann. Practical and Robust Secure Logging from Fault-Tolerant Sequential Aggregate Signatures. In: ProvSec 2017, Proceedings. Ed. by Tatsuaki Okamoto et al. LNCS 10592. Springer, 2017. pp. 87–106. [Full version], [Slides]
  12. Gunnar Hartung, Björn Kaidel, Alexander Koch, Jessica Koch, and Andy Rupp. Fault-Tolerant Aggregate Signatures. In: PKC 2016, Proceedings. Ed. by Chen-Mou Cheng et al. LNCS 9614. Springer, 2016. pp. 331–356. [Full version], [Slides by G. Hartung]
  13. Alexander Koch, Stefan Walzer, and Kevin Härtel. Card-based Cryptographic Protocols Using a Minimal Number of Cards. In: ASIACRYPT 2015, Proceedings. Ed. by Tetsu Iwata und Jung Hee Cheon. LNCS 9452. Springer, 2015. pp. 783–807. [Full version], [Slides]

Peer-Reviewed Journal Articles

  1. Samuel Hand, Alexander Koch, Pascal Lafourcade, Daiki Miyahara and Léo Robert. Efficient Card-Based ZKP for Single Loop Condition and Its Application to Moon-or-Sun. New Generation Computing 42, Special Issue on Card-Based Cryptography 3, pp. 449–477 (2024).
  2. Alexander Koch and Stefan Walzer. Private Function Evaluation with Cards. New Generation Computing 40, Special Issue on Card-Based Cryptography 2022, pp. 115–147 (2022). [ePrint version].
  3. Alexander Koch. The Landscape of Optimal Card-based Protocols. Mathematical Cryptology, Special Issue: Proceedings of MathCrypt 2021 (International Workshop on Mathematical Cryptology), 1(2), pp. 115–131 (2022). [ePrint-Version], [Slides].
  4. Johannes Ernst and Alexander Koch. Private Stream Aggregation with Labels in the Standard Model. Proceedings on Privacy Enhancing Technologies, PETS 2021 (4), pp. 117–138 (2021). (Extended abstract in: crypto day matters 32.) [Slides by J. Ottenhues]
  5. Brandon Broadnax, Alexander Koch, Jeremias Mechler, Tobias Müller, Jörn Müller-Quade and Matthias Nagel. Fortified Multi-Party Computation: Taking Advantage of Simple Secure Hardware Modules. Proceedings on Privacy Enhancing Technologies, PETS 2021 (4), pp. 312–338 (2021).
  6. Alexander Koch, Michael Schrempp and Michael Kirsten. Card-based Cryptography Meets Formal Verification. New Generation Computing 39, Special Issue on Card-Based Cryptography 2021, pp. 115–158 (2021). [Author's Accepted Version]

Invited Papers

  1. Alexander Koch. The Landscape of Security from Physical Assumptions. In: IEEE Information Theory Workshop, ITW 2021. [Full version], [Slides]

Theses

  1. Alexander Koch. Cryptographic Protocols from Physical Assumptions. Dissertation. Karlsruhe Institute of Technology (KIT), 2019. Supervision by Prof. Dr. Jörn Müller-Quade.
  2. Alexander Koch. Computational Arithmetic Secret Sharing and Secure Multiparty Computation. Diploma thesis. Karlsruhe Institute of Technology (KIT), 2014. Supervision by Prof. Dr. Dennis Hofheinz and PD Dr. Stefan Kühnlein.
  3. Alexander Koch. Representations of Graphs by Outside Obstacles. Study thesis. Karlsruhe Institute of Technology (KIT), 2012. Supervision by Dr. Marcus Krug, Prof. Dr. Ignaz Rutter and Prof. Dr. Takeshi Tokuyama.

Manuscripts in Preparation & Working Papers

  1. Alexander Koch, Marcus Krug, and Ignaz Rutter. Graphs with Plane Outside-Obstacle Representations. In: ArXiv e-prints (2013). ID: 1306.2978 [cs.CG].

Third-Party Funded Projects

I worked on the following projects (acquise by others).

KASTEL: Competence Center for Applied Security Technology.
KASTEL is one of the large IT security research centers in Germany, and recently morphed from a BMBF-funded long-term project to a Helmholtz-funded permanent institute.
SeReMo: Secure Remote Monitoring.
The project develops techniques for anonymized processing and monitoring of sensor data. To this aim, we consider encryption schemes that allow for performing specific computations and/or comparisons on encrypted data.
secUnity: Supporting the Security Community.
This cooperative project is funded by the Federal Ministry of Education and Research (BMBF) with the aim of strengthening European IT security research in Germany. For this aim, seven research groups at five locations collaborate closely.

Service, Professional Activities and Fellowships

Teaching

After successfully completing various courses in didactics for higher education, I was awarded the Baden-Württemberg Certificate for Teaching and Learning at University Level in 2017. Some links below go to the Web Archive.

Contact Information

E-Mail: alexander.koch(at)irif.fr.

You may also take a look at my former page at KIT.

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