This is the homepage of the research group “Cryptography and Complexity Theory” (Cryptoplexity). The group has been established in July 2011 at the Technische Universität Darmstadt as a Heisenberg-Professorship of the German Research Foundation DFG and has been supported through that program till June 2016 (see Projects->Heisenberg for more information).

Research Area

Our research area is complexity-based cryptography which investigates the relationship of (abstract or concrete) cryptographic problems, such as the security of complex cryptographic protocols built out of more fundamental cryptographic primitives. Our security proofs for the protocols of the new German identity card are a concrete example for our work.

Central to our research are the question of modelling (what does it mean to be secure?) and the notion of a reduction, originating from complexity theory and nowadays forming the common technique to conduct security proofs. We are interested in both the applications of these notions as well as the notions as a research topic themselves. This requires vivid interaction with related areas like complexity theory, IT security, number theory, or algorithmics.


We view ourselves as a research-oriented group which, in collaboration with national and international partners from research, industry and the public sector, enhances the areas of cryptography and IT security. Our actions are based on the Rules of Good Scientific Practice, as described for example by the German Research Foundation (DFG). And we're fun.


  • 2020/01/22

    IACR Board of Directors

    Marc Fischlin has been appointed to the IACR Board of Directors for 2020 and 2021.

  • 2020/01/16

    We're moving.

    Picture: pixabay / congerdesign

    From 10.02.2020 new address: Pankratiusstraße 2, 64289 Darmstadt (S2|20).

  • 2019/11/13

    Dr. Felix Günther mit ACM SIGSAC Doctoral Dissertation Award ausgezeichnet

    Dr. Felix Günther bei der Verleihung des Doctoral Dissertation Award

    Preis für herausragende Dissertationen in IT-Sicherheit

    Im Rahmen der diesjährigen Top-Security-Konferenz ACM CCS 2019 in London wurde Dr. Felix Günther am 13. November 2019 mit dem ACM SIGSAC Doctoral Dissertation Award ausgezeichnet. Der hochkompetitive Preis ehrt international exzellente Promotionsarbeiten im Bereich Computer- und IT-Sicherheit und ist mit 1.500 US-Dollar dotiert.

  • 2019/10/22

    Best Paper Award for CYSEC researchers

    CYSEC researchers Felix Günther and Jacqueline Brendel, Picutre: Chi Cheng

    For their paper about the Breakdown Resilience model the CYSEC researchers Jacqueline Brendel, Marc Fischlin, and Felix Günther won the Best Paper Award at the ESORICS Symposium 2019 in Luxembourg.