Privacy-Preserving Self-Sovereign Identity Systems with Key Recovery (CYD Doctoral Fellowship)

National digital identity systems, namely Swiss e-ID and EUDI, are going live in 2027. For such a system to be usable, it must provide account recovery, accountability, and uniqueness, without sacrificing user privacy. Cryptographic solutions to each have existed for decades, but they fail in deployment. The work in this fellowship hence co-designs cryptographic protocols with systems techniques to achieve these three properties with maximal privacy: Apollo recovers a vault from a user who remembers nothing, the cryptographic forensic trail makes credential misuse accountable under a search warrant, and Tutella deduplicates biometric enrollments while ensuring both query and database privacy with sublinear costs. The fellowship further aims to study Apollo’s usability and extend the above-mentioned three works under different threat models. Thus, the fellowship aims to provide three concrete building blocks for a digital identity system that can be potentially used for Swiss e-ID and EUDI.