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This paper introduces bPk#, a distributed architecture for electronic identities (eIDs) that enhances privacy and availability compared to the centralized Austrian bPk system. bPk# delegates pseudonym computation rights to users and service providers, minimizing metadata exposure to the central authority and reducing its availability demands. The authors provide a formal framework, a generic construction with security proofs, and a concrete instantiation with a reference implementation demonstrating practical efficiency.
Decentralizing eID pseudonym generation lets users control their data and reduces reliance on a single point of failure, offering a path to more robust and privacy-preserving national identity systems.
Electronic identities (eIDs) are crucial in an increasingly digitalized environment. Pseudonyms, as offered by Austria's governmental sector-specific personal identifiers (bPks), can significantly improve privacy by ensuring that personal data is not universally traceable across public services and private companies. However, the current architecture comes with several challenges regarding availability, privacy, and authenticity, due to a fully centralized design. This paper proposes bPk#, a distributed architecture to address these issues, reducing reliance on the central authority, while still providing all functional requirements to the existing bPk system. In particular, users are delegated the rights to compute their own pseudonyms, thereby minimizing metadata revealed to the central authority, while (subsets of) service providers may receive the right to compute pseudonyms only within their own domain, thereby reducing the availability needs of the central authority. To the best of our knowledge, we provide the first formal framework for such delegatable pseudonym systems, together with a generic construction for which we provide formal security proofs. Furthermore, we propose a concrete instantiation of our construction, together with a reference implementation demonstrating the practical efficiency.