Domain-Specific Pseudonymous Signatures Revisited

Domain-Specific Pseudonymous Signature schemes were recently proposed for privacy preserving authentication of digital identity documents by the BSI, German Federal Office for Information Security. The crucial property of domain-specific pseudonymous signatures is that a signer may derive unique pseudonyms within a so called domain. Now, the signer’s true identity is hidden behind his domain pseudonyms and these pseudonyms are unlinkable, i.e. it is infeasible to correlate two pseudonyms from distinct domains with the identity of a single signer. In this paper we take a critical look at the security definitions and constructions of domain-specific pseudonymous signatures proposed by far. We review two articles which propose “sound and clean” security definitions and point out some issues present in these models. Some of the issues we present may have a strong practical impact on constructions “provably secure” in this models. Additionally, we point out some worrisome facts about the proposed schemes and their security analysis.