109 research outputs found

    MoniPoly---An Expressive qq-SDH-Based Anonymous Attribute-Based Credential System

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    Modern attribute-based anonymous credential (ABC) systems benefit from special encodings that yield expressive and highly efficient show proofs on logical statements. The technique was first proposed by Camenisch and Groß, who constructed an SRSA-based ABC system with prime-encoded attributes that offers efficient AND, OR and NOT proofs. While other ABC frameworks have adopted constructions in the same vein, the Camenisch-Groß ABC has been the most expressive and asymptotically most efficient proof system to date, even if it was constrained by the requirement of a trusted message-space setup and an inherent restriction to finite-set attributes encoded as primes. In this paper, combining a new set commitment scheme and a SDH-based signature scheme, we present a provably secure ABC system that supports show proofs for complex statements. This construction is not only more expressive than existing approaches, it is also highly efficient under unrestricted attribute space due to its ECC protocols only requiring a constant number of bilinear pairings by the verifier; none by the prover. Furthermore, we introduce strong security models for impersonation and unlinkability under adaptive active and concurrent attacks to allow for the expressiveness of our ABC as well as for a systematic comparison to existing schemes. Given this foundation, we are the first to comprehensively formally prove the security of an ABC with expressive show proofs. Specifically, we prove the security against impersonation under the qq-(co-)SDH assumption with a tight reduction. Besides the set commitment scheme, which may be of independent interest, our security models can serve as a foundation for the design of future ABC systems

    Early Steroid Withdrawal Compared With Standard Immunosuppression in Kidney Transplantation - Interim Analysis of the Amsterdam-Leiden-Groningen Randomized Controlled Trial

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    BACKGROUND: The optimal immunosuppressive regimen in kidney transplant recipients, delivering maximum efficacy with minimal toxicity, is unknown. METHODS: The Amsterdam, LEiden, GROningen trial is a randomized, multicenter, investigator-driven, noninferiority, open-label trial in 305 kidney transplant recipients, in which 2 immunosuppression minimization strategies-one consisting of early steroid withdrawal, the other of tacrolimus minimization 6 months after transplantation-were compared with standard immunosuppression with basiliximab, corticosteroids, tacrolimus, and mycophenolic acid. The primary endpoint was kidney function. Secondary endpoints included death, primary nonfunction, graft failure, rejection, discontinuation of study medication, and a combined endpoint of treatment failure. An interim analysis was scheduled at 6 months, that is, just before tacrolimus minimization. RESULTS: This interim analysis revealed no significant differences in Modification of Diet in Renal Disease between the early steroid withdrawal group and the standard immunosuppression groups (43.2 mL/min per 1.73 m2 vs 45.0 mL/min per 1.73 m2, P = 0.408). There were also no significant differences in the secondary endpoints of death (1.0% vs 1.5%; P = 0.737), primary nonfunction (4.1% vs 1.5%, P = 0.159), graft failure (3.1% vs 1.5%, P = 0.370), rejection (18.6% vs 13.6%, P = 0.289), and discontinuation of study medication (19.6% vs 12.6%, P = 0.348). Treatment failure, defined as a composite endpoint of these individual secondary endpoints, was more common in the early steroid withdrawal group (P = 0.027), but this group had fewer serious adverse events and a more favorable cardiovascular risk profile. CONCLUSIONS: Based on these interim results, early steroid withdrawal is a safe short-term immunosuppressive strategy. Long-term outcomes, including a comparison with tacrolimus minimization after 6 months, will be reported in the final 2-year analysis

    On Linkability and Malleability in Self-blindable Credentials

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    Contains fulltext : 147332.pdf (preprint version ) (Open Access)13 p

    An Efficient Self-blindable Attribute-Based Credential Scheme

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