Cybersecurity – Identity Management

The research group Cybersecurity – Identity Management, led by Prof. Dr. Anja Lehmann, develops and analyzes cryptographic protocols with provable security guarantees. A focus is on privacy-preserving technologies, especially for identity management, where users must be authenticated and their data handled securely without sacrificing their privacy.

Provable security is the methodological core of modern cryptography: guarantees rest on formal models that make precise what security and privacy a protocol is meant to provide, and on rigorous proofs that reduce the security of a complex protocol to well-established assumptions about the simpler primitives it is built from. The group both applies these techniques to concrete systems and studies the underlying models and primitives, working from cryptographic foundations to applied protocols for real-world problems. A current example of the latter are the group's contributions to the European Digital Identity (EUDI) Wallet towards enabling the use of privacy-preserving credentials.

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05/26	Our group has new accepted papers at Crypto 2026 and SCN 2026: New Straight-Line Extractable NIZKPs for Cryptographic Group Actions. Andrea Flamini, Federico Pintore, Edoardo Signorini, Giovanni Tognolini. Crypto 2026. Orthus: Practical Sublinear Batch-Verification of Lattice Relations from Standard Assumptions. Madalina Bolboceanu, Jonathan Bootle, Vadim Lyubashevsky, Antonio Merino-Gallardo, and Gregor Seiler. Crypto 2026. Proof-Carrying Data via Holography Accumulation. Nikitas Paslis, Carla Ràfols, Alexandros Zacharakis. SCN 2026. Signatures with Post-Compromise Accountability. Dennis Dayanikli, Johannes Lang, Anja Lehmann. SCN 2026 -- based on Johannes Master's Thesis.
05/26	Busy week at Eurocrypt: Karla, Cavit, Andrea, Alexandros and Anja presented their works at the largest cryptography concerence and affiliated workshops MORE
04/26	We welcome Vera Wesselkamp as new PhD student in our group!
03/26	Our group hosted the 11th edition of the Young Researcher Crypto Seminar, led by PhD students Karla Friedrichs, Cavit Özbay, Andrey Sidorenko, and assistant Mélanie Angoujard. MORE
01/26	Two papers have been accepted at the IACR Eurocrypt conference: "Device-Bound Anonymous Credentials With(out) Trusted Hardware" by Karla Friedrichs, Franklin Harding, Anja Lehmann, Anna Lysyanskaya, and "Putting Multi into Multi-Signatures: Tight Security for Multiple Signers" by Anja Lehmann and Cavit Özbay. Congrats!
01/26	Anja Lehmann gave a keynote presentation on "The wonderful world of cryptographic pseudonyms" at the DSK European Data Privacy Day.
12/25	Awards for excellent master theses: Karla Friedrichs hat won the 1st and Konrad Hanff the 3rd price of the CAST-Award IT-Security 2025 for their master theses. Congratulations!
12/25	Anja Lehmann gave a joint invited talk "EUDI Wallet: Perspectives and Challenges for ZKP and PQC" with Gregor Seiler at the European Conference on PQC Migration in Den Haag.
11/25	The paper "Multi-Party Private Join" by Anja Lehmann, Christian Mouchet and Andrey Sidorenko has been accepted at PETS 2026. The paper is based on Andrey's Master thesis. Congratulations!
11/25	Anja Lehmann participated in the Falling Walls Science Summit, and discussed “Hidden Structures: The Secret Life of your Digital Footprint” together with Felix Naumann.
10/25	Two papers on anonymous credentials have been accepted at the Security Standardisation Research Conference 2025: "SoK: Anonymous Credentials for Digital Identity Wallets" by Christian Bormann and Anja Lehmann, as well as "Vision: A Modular Framework for Anonymous Credential Systems" by Anja Lehmann, Andrey Sidorenko and Alexandros Zacharakis. Both works were done in the context of the EUDI project with SPRIND.
10/25	Anja Lehmann gave a presentation on ZKP Innovation Highlights at the SPRIND Funke conference on EUDI Wallet Prototypes.
10/25	We welcome Dr. Andrea Flamini to our team, who is joining as a Postdoc!
09/25	We support the recent Open Letter against EU's plans for chat control, which has been signed by more than 800 scientists.
08/25	The paper "Game Changer: A Modular Framework for OPRF Security" by Karla Friedrichs, Anja Lehmann and Cavit Özbay has been accepted at IACR Asiacrypt 2025. The paper is based on Karla's Master thesis. Congratulations!
08/25	We welcome Dr. Alexandros Zacharakis to our team, who is joining as a Postdoc!
07/25	Two papers have been accepted at ACM CCS 2025: "Updatable aPAKE: Security Against Bulk Precomputation Attacks" by Dennis Dayanikli and Anja Lehmann; and "Security Analysis of Privately Verifiable Privacy Pass" by Konrad Hanff, Anja Lehmann and Cavit Özbay, based on the Master thesis of Konrad.
07/25	The paper "Accurate and Composable Noise Estimates for CKKS with Application to Exact HE Computation" by Jean-Philippe Bossuat, Anamaria Costache, Christian Mouchet, Lea Nürnberger and Juan Ramón Troncoso-Pastoriza was accepted in the IACR Communications in Cryptology journal.
05/25	Double the Honors: Teaching and Graduation Awards for the Team! Our research group lead Anja Lehmann has been awarded the Teaching Award for outstanding dedication to education! And to top it off, Karla Friedrichs received the Graduation Award. Congratulations! We’re also proud that the team for the lecture „Introduction to Cryptography“ (Anja Lehmann, Dennis Dayanikli, Karla Friedrichs, Andrey Sidorenko, and Ronja Wagner) was nominated for the Teaching Team Award. Congratulations to the awardees and to the team! MORE

Picture of Award Acceptation — Ronja Wagner, Andrey Sidorenko, and Karla Friedrichs accept the Teaching Award on behalf of Prof. Anja Lehmann. (Photo: Nicole Krüger/HPI)

05/25	We welcome Andrey Sidorenko, starting his PhD, in our group!
04/25	We welcome Karla Friedrichs, starting her PhD, in our group!
03/25	Anja Lehmann gave a talk on "EU Digital Identity & Anonymous Credentials: A Happy End?" at Real-World Crypto 2025, the video is available here.
02/25	Three papers got accepted at PKC 2025: "Commit-and-Prove System for Vectors and Applications to Threshold Signing" by Anja Lehmann and Cavit Özbay "Privacy-Preserving Multi-Signatures: Generic Techniques and Constructions Without Pairings" by Calvin Abou Haidar (NTT), Dipayan Das (NTT), Anja Lehmann, Cavit Özbay and Octavio Perez Kempner (NTT) "Efficient Verifiable Mixnets from Lattices, Revisited" by Jonathan Bootle (IBM Research), Vadim Lyubashevsky (IBM Research) and Antonio Merino-Gallardo (IBM Research & University of Potsdam)
02/25	The paper "Stronger Security for Threshold Blind Signatures" by Anja Lehmann, Phillip Nazarian (UCI) and Cavit Özbay was accepted at Eurocrypt 2025.
02/25	Dennis Dayanikli is presenting our works on the security of the SRP protocol and stronger aPAKE models at the PAKE'25 workshop.
12/24	Anja Lehmann gave a joint presentation with Thomas Lohninger on "EU's Digital Identity Systems - Reality Check and Techniques for Better Privacy" at the 38c3.
12/24	Eric Ackermann has won the CAST Award for his master thesis "SEKA: Secretless Key Exchange and Authentication in LiFi Networks". Congratulations!
12/24	The paper "OPPID: Single Sign-On with Oblivious Pairwise Pseudonyms" by Maximilian Kroschewski, Anja Lehmann and Cavit Özbay has been accepted at PETS 2025.
11/24	Cordian Daniluk presented his paper "Zeros Are Heroes: NSEC3 Parameter Settings in the Wild" at the ACM IMC 2024 conference.
10/24	Christian Mouchet presented his works "Helium: Scalable MPC among Lightweight Participants and under Churn" and "Multiparty Private Set Intersection from Multiparty Homomorphic Encryption" at ACM CCS 2024. For Helium, he also won the Distinguished Artifact Award. Congrats!
09/24	We support the Open Letter against the EU's plans to impose chat control on encrypted communication.

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