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My Research

I am currently a postdoctoral researcher at the Karlsruhe Institute of Technology (KIT).

My general research interests are Digital Signatures, Building Blocks, Lattice-Based Cryptography, Hardware Assumptions in Cryptography, Card-Based Cryptography, Universal Composability, Algebraic Geometric Codes, Quantum Cryptography.

My current research focus is on Improving Science with Cryptography, Secure Multiparty Computation for the Social Good, Cryptography and Machine Learning, Digital Contact Tracing.

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


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

Peer-Reviewed Conference Papers

  1. Sebastian Faller and Pascal Baumer and Michael Klooß and Alexander Koch and Astrid Ottenhues and Markus Raiber. Black-Box Accumulation Based on Lattices. Accepted for publication in: IMA International Conference on Cryptography and Coding, IMACC 2021. LNCS. Springer, 2021. [Full version].
  2. 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. Accepted for publication in: ASIACRYPT 2021, Proceedings. Ed. by Mehdi Tibouchi and Huaxiong Wang. LNCS 13091. Springer, 2021. [Full version].
  3. 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.
  4. Alexander Koch, Michael Schrempp, and Michael Kirsten. Card-based Cryptography Meets Formal Verification. In: ASIACRYPT 2019, Proceedings, Part I. Ed. by Steven Galbraith and Shiho Moriai. LNCS 11921. Springer, 2019. pp. 488–517. [Full version], [Slides]
  5. 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]
  6. 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, Part III. Ed. by Takagi Tsuyoshi and Thomas Peyrin. LNCS 10626. Springer, 2017, pp. 126–155. [Full version], [Slides, Copy part by D. Miyahara]
  7. 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]
  8. Gunnar Hartung, Björn Kaidel, Alexander Koch, Jessica Koch, and Andy Rupp. Fault-Tolerant Aggregate Signatures. In: PKC 2016, Proceedings, Part I. Ed. by Chen-Mou Cheng et al. LNCS 9614. Springer, 2016. pp. 331–356. [Full version], [Slides by G. Hartung]
  9. Alexander Koch, Stefan Walzer, and Kevin Härtel. Card-based Cryptographic Protocols Using a Minimal Number of Cards. In: ASIACRYPT 2015, Proceedings, Part I. Ed. by Tetsu Iwata und Jung Hee Cheon. LNCS 9452. Springer, 2015. pp. 783–807. [Full version], [Slides]

Peer-Reviewed Journal Articles

  1. Alexander Koch and Stefan Walzer. Private Function Evaluation with Cards. Accepted for publication in: New Generation Computing Special Issue on Card-Based Cryptography 2022. [ePrint version].
  2. Alexander Koch. The Landscape of Optimal Card-based Protocols. Accepted at: Journal of Mathematical Cryptology, Special Issue: Proceedings of MathCrypt 2021 (International Workshop on Mathematical Cryptology). [ePrint-Version], [Slides].
  3. 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. (Extended abstract in: crypto day matters 32.) [Slides by J. Ernst]
  4. 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.
  5. 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]


  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.

Invited Papers

  1. Alexander Koch. The Landscape of Security from Physical Assumptions. To appear in: IEEE Information Theory Workshop, ITW 2021. [Slides]

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. See it-security-map.eu.

Service and Professional Activities


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

See also my page at KIT.

Building 50.34, Room 274,
Am Fasanengarten 5,
76131 Karlsruhe, Germany.

Phone: +49 721 608-44256.
E-Mail: alexander.koch(at)kit.edu (S/MIME certificate).

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