A Practical System for Globally Revoking the Unlinkable Pseudonyms of Unknown Users

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Abstract

We propose the first single sign-on system in which a user can access services using unlinkable digital pseudonyms that can all be revoked in case she abuses any one service. Our solution does not rely on key escrow: a user needs to trust only her own computing device with following our protocols in order to be assured of the unconditional untraceability and unlinkability of her pseudonyms. Our solution involves two novel ingredients: a technique for invisibly chaining the user’s pseudonyms such that all of them can be revoked on the basis of any one of them (without knowing the user’s identity with the issuer) and a sublinear-time proof that a committed value is not on a list without revealing additional information about the value. Our solution is highly practical.