Doreen Riepel
I am a tenure-track faculty member at CISPA Helmholtz Center for Information Security, where I am part of the research area Algorithmic Foundations and Cryptography. My group focuses mainly on provable security. Previously, I was a postdoctoral researcher at UC San Diego working with Mihir Bellare. I received my PhD from Ruhr University Bochum under the supervision of Eike Kiltz.
My research lies at the intersection of cryptography and provable security. I study the theoretical foundations of cryptographic schemes and protocols used in practice, with the goal of obtaining strong and concrete security guarantees. My work combines the analysis of existing cryptographic constructions with the design of new protocols and security models. I am particularly interested in authenticated key exchange, secure messaging, advanced encryption schemes, post-quantum cryptography, and tight security reductions. Recent work includes contributions to group and ratcheted key exchange, updatable and attribute-based encryption, cryptographic group actions and isogeny-based cryptography, and formal models for modern cryptographic protocols.
More broadly, I aim to increase the rigor and reliability of cryptographic research. For example, I am interested in computer-assisted proofs and the formal verification of security arguments, with the goal of bringing provable security closer to techniques from formal methods. I am also interested in strengthening the foundations of isogeny-based cryptography by better aligning provable security techniques with the underlying mathematics..
Publications
Preprints
IACR Cryptology ePrint Archive, 2025
2026
Annual International Cryptology Conference (CRYPTO)
Annual International Conference on the Theory and Applications of Cryptographic Techniques (EUROCRYPT)
Annual International Conference on the Theory and Applications of Cryptographic Techniques (EUROCRYPT)
2025
IACR Transactions on Cryptographic Hardware and Embedded Systems (CHES)
IACR International Conference on Practice and Theory of Public-Key Cryptography (PKC)
IACR International Conference on Practice and Theory of Public-Key Cryptography (PKC)
IEEE Conference on Secure and Trustworthy Machine Learning (SaTML)
2024
International Conference on the Theory and Application of Cryptology and Information Security (ASIACRYPT)
International Conference on the Theory and Application of Cryptology and Information Security (ASIACRYPT)
International Conference on the Theory and Application of Cryptology and Information Security (ASIACRYPT)
ACM Conference on Computer and Communications Security (CCS)
ACM Conference on Computer and Communications Security (CCS)
Annual International Conference on the Theory and Applications of Cryptographic Techniques (EUROCRYPT)
Post-Quantum Cryptography (PQCrypto)
2023
Topics in Cryptology – CT-RSA
IACR International Conference on Practice and Theory of Public-Key Cryptography (PKC)
USENIX Security Symposium
2022
International Conference on the Theory and Application of Cryptology and Information Security (ASIACRYPT)
International Conference on the Theory and Application of Cryptology and Information Security (ASIACRYPT)
ACM Conference on Computer and Communications Security (CCS)
Annual International Cryptology Conference (CRYPTO)
2021
Annual International Cryptology Conference (CRYPTO)
Annual International Conference on the Theory and Applications of Cryptographic Techniques (EUROCRYPT)
Annual International Conference on the Theory and Applications of Cryptographic Techniques (EUROCRYPT)
Projects
Crypto Proof Ladders
The Crypto Proof Ladders project aims to provide a gentle introduction to formal methods for cryptography. The main idea is to present a collection of cryptographic problems with increasing levels of difficulty, formalized both as traditional pen-and-paper proofs and within different proof tools. The project is an initiative that originated from the HACS workshop and brings together cryptographers, cryptography engineers, and formal methods researchers. In this context, Paul Rösler and I contributed game-based definitions and proofs for unilateral authenticated key exchange protocols, available here. An EasyCrypt translation of the proof, mainly driven by François Dupressoir, is currently a work in progress.
Additional tools and resources are listed below.
PELICAN
The PELICAN project is an Équipe Associée with Inria, led by Sabrina Kunzweiler and myself. Funded by Inria, PELICAN focuses on the foundations of provable security for isogeny-based cryptographic protocols, and supports visits between our groups to foster closer collaboration.
PQarrots
I am part of the PQarrots submission to the NIST Threshold Cryptography Call. We propose post-quantum threshold primitives based on isogeny-based group actions, including threshold signatures, public-key encryption, and distributed key generation. A preview is available here. A more detailed version with full specifications, implementation details, and security proofs will follow.
Service
Program Committees
Reviewing
Other
Organization
Resources
Tools for Cryptographers
I am generally interested in tools that support rigorous cryptographic proofs. While I am currently not involved in the development of such tools myself, I am actively supporting this area and am always happy to discuss ideas in this direction. Below are a few tools and resources developed by members of the community that I find particularly interesting:
- ProofFrog is a light-weight and easy-to-learn tool that checks game-hopping proof transitions in reduction-based security proofs.
- Domino is a tool to write and verify cryptographic proofs in the State-Separation Proofs framework. It can manage more tedious aspects, as they often come up in proofs for key exchange protocols.
- EasyCrypt is an interactive framework for machine-checked proofs of cryptographic schemes and protocols in the computational model. It is a very powerful tool, therefore not so easy to learn.
A direction that I find particularly interesting is how cryptographic proofs can be made more readable and interactive. Beyond traditional static LaTeX documents (who does ever read appendices), I believe that future proof presentations could allow structured navigation through games, reductions, and assumptions, making complex arguments easier to follow and verify. Related resources include:
- TeXFrog supports writing game-hopping proofs in LaTeX by automatically generating per-game renderings with highlighted differences.
- The Joy of Cryptography is a free undergraduate-level textbook by Mike Rosulek that introduces the fundamentals of provable security. The new web version is a nice example of presenting cryptographic content in a more structured and interactive way.
Talks