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Item type:Publication, Access status: without files , Non-interactive threshold BBS+ from pseudorandom correlations(Springer, 2025-04); ; ; ; The BBS+ signature scheme is one of the most prominent solutions for realizing anonymous credentials. Its prominence is due to properties like selective disclosure and efficient protocols for creating and showing possession of credentials. Traditionally, a single credential issuer produces BBS+ signatures, which poses significant risks due to a single point of failure.I n this work, we address this threat via a novel t-out-of-n threshold BBS+ protocol. Our protocol supports an arbitrary security threshold t≤n and works in the so-called preprocessing setting. In this setting, we achieve non-interactive signing in the online phase and sublinear communication complexity in the number of signatures in the offline phase, which, as we show in this work, are important features from a practical point of view. As it stands today, none of the widely studied signature schemes, such as threshold ECDSA and threshold Schnorr, achieve both properties simultaneously. In this work, we make the observation that presignatures can be directly computed from pseudorandom correlations which allows servers to create signatures shares without additional cross-server communication. Both our offline and online protocols are actively secure in the Universal Composability model. Finally, we evaluate the concrete efficiency of our protocol, including an implementation of the online phase and the expansion algorithm of the pseudorandom correlation generator (PCG) used during the offline phase. The online protocol without network latency takes less than 14 ms for t≤30 and credentials sizes up to 10. Further, our results indicate that the influence of t on the online signing is insignificant, ≤6% for t≤30, and the overhead of the thresholdization occurs almost exclusively in the offline phase. Our implementation of the PCG expansion shows that even for a committee size of 10 servers, each server can expand a correlation of up to 217 presignatures in less than 100 ms per presignature.Publicationtype: Conference Paper30 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Combined fault and leakage resilience : composability, constructions and compiler(Springer, 2023-08-09); ; ; ; Real-world cryptographic implementations nowadays are not only attacked via classical cryptanalysis but also via implementation attacks, including passive attacks (observing side-channel information about the inner computation) and active attacks (inserting faults into the computation). While countermeasures exist for each type of attack, countermeasures against combined attacks have only been considered recently. Masking is a standard technique for protecting against passive side-channel attacks, but protecting against active attacks with additive masking is challenging. Previous approaches include running multiple copies of a masked computation, requiring a large amount of randomness or being vulnerable to horizontal attacks. An alternative approach is polynomial masking, which is inherently fault-resistant. This work presents a compiler based on polynomial masking that achieves linear computational complexity for affine functions and cubic complexity for non-linear functions. The resulting compiler is secure against attackers using region probes and adaptive faults. In addition, the notion of fault-invariance is introduced to improve security against combined attacks without the need to consider all possible fault combinations. Our approach has the best-known asymptotic efficiency among all known approaches.Publicationtype: Conference Paper19