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 he or she abuses any one service. Our solution does not rely on key escrow: each 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. In applications where users hook pseudonyms up to legacy identifiers or legacy accounts at service providers, our system guarantees that service providers (even if they collude with the pseudonym issuer) do not gain any correlation powers over users. Our solution involves two novel ingredients: a technique for invisibly chaining all of a user's pseudonyms in a manner that permits the revocation of all of them 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 number is not on a blacklist without revealing additional information about the number. Our solution is highly practical. CR AbstractWe 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 he or she abuses any one service. Our solution does not rely on key escrow: each 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. In applications where users hook pseudonyms up to legacy identifiers or legacy accounts at service providers, our system guarantees that service providers (even if they collude with the pseudonym issuer) do not gain any correlation powers over users. Our solution involves two novel ingredients: a technique for invisibly chaining all of a user's pseudonyms in a manner that permits the revocation of all of them 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 number is not on a blacklist without revealing additional information about the number. Our solution is highly practical.

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Abstract. Real world healthcare systems are generally large and overly complex systems. Designing privacy-friendly protocols for such systems is a challenging task. In this paper we present a privacy-preserving protocol for the Belgian healthcare system. The proposed protocol protects the patients' privacy throughout the prescription handling process, while complying with most aspects of the current Belgian healthcare practise. The presented protocol relies on standard privacy-preserving credential systems, and verifiable public key cryptography, which makes it readily fit for implementation.

Abstract.In an increasing information-driven society, preserving privacy is essential. Anonymous credentials promise a solution to protect the user's privacy. However, to ensure accountability, efficient revocation mechanisms are essential. Having classified existing revocation strategies, we implemented one variant for each. In this paper we describe our classification and compare our implementations. Finally, we present a detailed analysis and pragmatic evaluation of the strategies.

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