Prof. Dr.-Ing. Tibor Jager

Dr.-Ing. Kai Gellert

Akademischer Rat
(tenured researcher)


Campus Freudenberg
Building FME, Room 2.12

Google Scholar

Short Vita

I work as a tenured researcher (Akademischer Rat) at the chair for IT Security and Cryptography since 2021. Before that I was a research assistant (and PhD student) at Paderborn University from 2017-2019 and at University of Wuppertal from 2019-2021. I completed my PhD with distinction in 2020 at University of Wuppertal under the supervision of Tibor Jager and with Colin Boyd as second examiner. I hold a bachelor's and master's degree in "IT Security and Information Engineering" from Ruhr University Bochum, which I completed from 2012-2015 and 2015-2017 respectively.

My research interests lie at the intersection of theoretical and real-world cryptography, where I enjoy analyzing and improving the security of real-world communication protocols. This includes, e.g., the analysis of complex protocols such as TLS 1.3 in its various handshake modes, developing efficient protocols with tailored security properties, or investigating if certain security properties are possible or even impossible to achieve in practice (and how to potentially overcome those impossibilites).

Honors and Awards

Independent Teaching Experience

During my time at the University of Wuppertal, I have independently taught the following courses:

  • Grundlagen der IT-Sicherheit (WiSe 2022/23, gemeinsam mit Tibor Jager)
  • Moderne Kryptographie (SoSe 2022, SoSe 2023)
  • Effiziente Implementierung kryptographischer Verfahren (WiSe 2020/21, WiSe 2021/22, WiSe 2022/23)
  • Communication Security for Modern Applications (SoSe 2021)

In addition, I have independently supervised and examined > 10 bachelor's and master's theses.

Academic Service

I have served as an external reviewer for the following conferences and journals:

  • 2022: EUROCRYPT, CRYPTO, ESORICS, IEEE Transactions on Dependable and Secure Computing (TDSC), IEEE Transactions on Mobile Computing (TMC)
  • 2021: IEEE S&P, ESORICS, ITC
  • 2020: Journal of Cryptology, ASIACRYPT, ASIACCS, ISC
  • 2018: CCS, ACNS, CT-RSA
  • 2017: PKC, ISC

Peer-Reviewed Publications


  • Gareth T. Davies, Sebastian Faller, Kai Gellert, Tobias Handirk, Julia Hesse, Máté Horvath, Tibor Jager
    Security Analysis of the WhatsApp End-to-End Encrypted Backup Protocol
    43th Annual International Cryptology Conference - CRYPTO 2023
  • Kai Gellert, Kristian Gjøsteen, Håkon Jacobsen, Tibor Jager
    On Optimal Tightness for Key Exchange with Full Forward Secrecy via Key Confirmation
    43th Annual International Cryptology Conference - CRYPTO 2023





Doctoral Dissertation

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