Elliptic curve digital signature algorithm

Résumé

Elliptic Curve Digital Signature Algorithm (ECDSA) est un algorithme de signature numérique à clé publique, variante de DSA. Il fait appel à la cryptographie sur les courbes elliptiques. Introduction L’algorithme a été proposé en 1992 par Scott Vanstone, en réponse à un appel d'offres pour les signatures numériques du National Institute of Standards and Technology (NIST). Vanstone fonda la société Certicom en 1985, et son entreprise détient la plupart des brevets des algorithmes à base de courbes elliptiques. Les avantages de ECDSA sur DSA et RSA sont des longueurs de clés plus courtes et des opérations de signature et de chiffrement plus rapides. ECDSA est défini par le standard ANSI X9.62-1998, Public Key Cryptography For The Financial Services Industry: The Elliptic Curve Digital Signature Algorithm (ECDSA). Algorithme Soit une courbe de formule y^2 = x^3 + ax + b. C'est une courbe elliptique sur un corps d'entiers fini modulo p avec p un nombre

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present several optimizations to SPHINCS, a stateless hash-based signature scheme proposed by Bernstein et al. in (2015): PORS, a more secure variant of the HORS few-time signature scheme used in SPHINCS; secret key caching, to speed-up signing and reduce signature size; batch signing, to amortize signature time and reduce signature size when signing multiple messages at once; mask-less constructions to reduce the key size and simplify the scheme; and Octopus, a technique to eliminate redundancies from authentication paths in Merkle trees. Based on a refined analysis of the subset resilience problem, we show that SPHINCS' parameters can be modified to reduce the signature size while retaining a similar security level and computation time. We then propose Gravity-SPHINCS, our variant of SPHINCS embodying the aforementioned tricks. Gravity-SPHINCS has shorter keys (32 and 64 bytes instead of approximate to 1 KB), shorter signatures (approximate to 30 KB instead of 41KB), and faster signing and verification for the same security level as SPHINCS.

SPRINGER INTERNATIONAL PUBLISHING AG2018

Chargement

Forgery-Resilience for Digital Signature Schemes

Atefeh Mashatan, Khaled Ouafi

We introduce the notion of forgery-resilience for digital signature schemes, a new paradigm for digital signature schemes exhibiting desirable legislative properties. It evolves around the idea that, for any message, there can only be a unique valid signature, and exponentially many acceptable signatures, all but one of them being spurious. This primitive enables a judge to verify whether an alleged forged signature is indeed a forgery. In particular, the scheme considers an adversary who has access to a signing oracle and an oracle that solves a “hard” problem, and who tries to produce a signature that appears to be acceptable from a verifier’s point of view. However, a judge can tell apart such a spurious signature from a signature that is produced by an honest signer. This property is referred to as validatibility. Moreover, the scheme provides undeniability against malicious signers who try to fabricate spurious signatures and deny them later by showing that they are not valid. Last but not least, trustability refers to the inability of a malicious judge trying to forge a valid signature. This notion for signature schemes improves upon the notion of fail-stop signatures in different ways. For example, it is possible to sign more than one messages with forgery-resilient signatures and once a forgery is found, the credibility of a previously signed signature is not under question. A concrete instance of a forgery-resilient signature scheme is constructed based on the hardness of extracting roots of higher residues, which we show to be equivalent to the factoring assumption. In particular, using collision-free accumulators, we present a tight reduction from malicious signers to adversaries against the factoring problem. Meanwhile, a secure pseudorandom function ensures that no polynomially-bounded cheating verifier, who can still solve hard problems, is able to forge valid signatures. Security against malicious judges is based on the RSA assumption.

2012

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MATHICSE Technical Report : Analytical and numerical study of a modified cell problem for the numerical homogenization of multiscale random fields

Assyr Abdulle, Doghonay Arjmand, Edoardo Paganoni

A central question in numerical homogenization of partial differential equations with multiscale coefficients is the accurate computation of effective quantities, such as the homogenized coefficients. Computing homogenized coefficients requires solving local corrector problems followed by upscaling relevant local data. The most naive way of computing homogenized coefficients is by solving a local elliptic problem, which is known to suffer from the so-called resonance error dominating all other errors inherent in multiscale computations. A far more efficient modelling strategy, based on adding an exponential correction term to the standard local elliptic problem, has recently been proved to result in exponentially decaying error bounds with respect to the size of the local geometry. The ques- tions in relation with the accuracy and computational efficiency of this approach has been previously addressed in the context of periodic homogenization. The present article concerns the extension of mathematical and numerical study of this modified elliptic corrector problem to stochastic homog- enization problems. In particular, we assume a stationary, ergodic micro-structure and i) establish the well-posedness of the corrector equation, ii) analyse the bias (or the systematic error) originat- ing from additional exponential correction term in the model. Numerical results corroborating our theoretical findings are presented.

EPFL2020

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Forgery-Resilience for Digital Signature Schemes

Atefeh Mashatan, Khaled Ouafi

2012