Philipp-Florens Lehwalder
Portrait of Philipp-Florens Lehwalder

Philipp-Florens Lehwalder

PhD student in privacy-preserving cryptography

I am a third-year PhD student at the Chair of Applied Cryptography at TU Darmstadt, advised by Prof. Sebastian Faust. My research is in privacy-preserving cryptography, with a focus on anonymous credentials and zero-knowledge proofs for Internet-scale systems. I earned an M.Sc. in IT Security and a B.Sc. in Computer Science from TU Darmstadt. Before starting my PhD, I worked full-time on the European Digital Identity Wallet at Lissi. Currently, I am a Research Engineer Intern at Cloudflare.

Publications

  1. Do You Need a Receipt? Anonymous Credential Revocation at Continental Scale via Private Record Certification
    Kasra Edalatnejad, Sebastian Faust, Jonas Hofmann, Philipp-Florens Lehwalder, Thomas Schneider.
    USENIX Security 2026.
    Summary

    We present a privacy-preserving, real-time revocation system for anonymous credentials with decentralized revocation authorities. It is based on a novel primitive called Private Record Certification, which lets users obtain a certificate for a database record without the servers learning which record was queried. Our prototype scales to over one billion credentials with sub-second latency.

  2. PIRANHAS: PrIvacy-Preserving Remote Attestation in Non-Hierarchical Asynchronous Swarms
    Jonas Hofmann, Philipp-Florens Lehwalder, Shahriar Ebrahimi, Parisa Hassanizadeh, Sebastian Faust.
    NDSS Symposium 2026.
    Summary

    PIRANHAS transforms any traditional remote attestation scheme into a transparent, non-interactive, and anonymous one using zk-SNARKs. It uses recursive zk-SNARKs to aggregate attestations of an entire IoT swarm into one succinct proof, revealing only the number of devices while hiding their identifiers. An open-source Noir and Plonky2 implementation achieves 356 ms aggregation time.

  3. UPPR: Universal Privacy-Preserving Revocation
    Leandro Rometsch, Philipp-Florens Lehwalder, Anh-Tu Hoang, Dominik Kaaser, Stefan Schulte.
    IEEE Blockchain 2025.
    Summary

    We present UPPR, a revocation mechanism for one-show verifiable credentials and anonymous credentials. Credential-specific VRF tokens are stored in a Bloom filter cascade on a blockchain; verifiers check whether a presented token is absent, while holders remain offline at negligible local cost. UPPR builds the revocation artifact for one million one-show credentials in 4.23 s.

  4. BIP32-Compatible Threshold Wallets
    Poulami Das, Andreas Erwig, Sebastian Faust, Philipp-Florens Lehwalder, Julian Loss, Ziyan Qu, Siavash Riahi.
    ACM AsiaCCS 2025.
    Summary

    We present the first threshold blockchain wallet fully compatible with the widely adopted BIP32 standard for hierarchical key derivation. The construction distributes secret keys across devices, avoiding a single point of failure while handling BIP32 derivations efficiently. It outperforms a generic MPC baseline by over 3,000 times.

  5. Poster: Secure and Differentially Private kth Ranked Element
    Gowri R. Chandran, Philipp-Florens Lehwalder, Leandro Rometsch, Thomas Schneider.
    Poster, ACM CCS 2023.
    Summary

    We add differential privacy to a secure multi-party protocol for computing the kth ranked element, protecting information otherwise leaked to a central party with only a minimal impact on accuracy.