Søren Eller Thomsen

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About Me

/portrait_aarhus.jpg I am a Senior Cryptographic Engineer at Partisia, where I work on applied cryptography - primarily identity systems, multi-party computation, and blockchain protocols. Recently I have become increasingly interested in digital identity: how people can prove things about themselves, share credentials, and interact with institutions without giving up more information than strictly necessary. This has drawn me into self-sovereign identity systems and the technical standards being developed for the EU Digital Identity Wallet.

Before joining Partisia, I worked at the Alexandra Institute, where I was involved in designing privacy-enhancing systems and carrying out security analyses.

I completed my PhD in computer science at Aarhus University, supervised by Jesper Buus Nielsen, where I also did my undergraduate studies. My research focused on the security of peer-to-peer networks and consensus protocols in the blockchain setting.

Manuscripts and Publications

Peer-to-peer Networks

  • Optimistic Message Dissemination
    Chen-Da Liu-Zhang, Christian Matt, and Søren Eller Thomsen.
    Advances in Financial Technologies (AFT) 2025.
    PDF - BibTeX
  • Asymptotically Optimal Message Dissemination with Applications to Blockchains
    Chen-Da Liu-Zhang, Christian Matt, and Søren Eller Thomsen.
    Advances in Cryptology - EUROCRYPT 2024.
    PDF - BibTeX - Slides
  • Practical Provably Secure Flooding for Blockchains
    Chen-Da Liu-Zhang, Christian Matt, Ueli Maurer, Guilherme Rito, and Søren Eller Thomsen.
    Advances in Cryptology - ASIACRYPT 2022.
    PDF - BibTeX - Slides - GitHub - Trailer - Video
  • Formalizing Delayed Adaptive Corruptions and the Security of Flooding Networks
    Christian Matt, Jesper Buus Nielsen, and Søren Eller Thomsen.
    Advances in Cryptology - CRYPTO 2022.
    PDF - BibTeX - Slides - Trailer - Video

Consensus

  • Enig: Player Replaceable Finality Layers with Optimal Validity
    Simon Holmgaard Kamp, Jesper Buus Nielsen, Søren Eller Thomsen, and Daniel Tschudi. 2022.
    PDF - BibTeX
  • Weight-Based Nakamoto-Style Blockchains
    Simon Holmgaard Kamp, Bernardo Magri, Christian Matt, Jesper Buus Nielsen, Søren Eller Thomsen, and Daniel Tschudi.
    Progress in Cryptology - LATINCRYPT 2021.
    PDF - BibTeX - Slides - Trailer - Video
  • Formalizing Nakamoto-Style Proof of Stake
    Søren Eller Thomsen and Bas Spitters.
    IEEE 34th Computer Security Foundations Symposium (CSF), 2021.
    PDF - BibTeX - Slides - GitHub - Video

Misc.

  • A Dependently Typed Library for Static Information-Flow Control in Idris
    Simon Gregersen, Søren Eller Thomsen, and Aslan Askarov.
    Principles of Security and Trust (POST), 2019.
    PDF - BibTeX - GitHub

PhD Thesis