Description
Digital signatures were introduced to guarantee the authenticity and integrity of the underlying messages. However, and in situations where the signed data is commercially or personally sensitive, the universal verification of digital signatures is undesirable, and needs to be limited or controlled. Therefore, mechanisms which share most properties with digital signatures except the universal verification were invented to respond to the aforementioned need; we call such mechanisms ``opaque signatures''. In this talk, we study confirmer signatures where the verification cannot be achieved without the cooperation of a specific entity, i.e. the confirmer, via the so-called confirmation/denial protocols. Generic constructions of designated confirmer signatures follow one of the following two strategies; either produce a digital signature on the message to be signed, then encrypt the resulting signature, or produce a commitment on the message, encrypt the string used to generate the commitment, and finally sign the latter. In this talk, we revisit both methods and establish the minimal and sufficient assumptions on the building blocks in order to attain secure confirmer signatures. Our study concludes that both paradigms, when used in their basic form, cannot allow a class of encryption schemes which is vital for the efficiency of the confirmation/denial protocols. Next, we propose a variation of both paradigms which thrives on very cheap encryption and consequently leads to efficient confirmer signatures. Indeed, the resulting constructions do not only compete with the dedicated realizations of confirmer/undeniable signatures proposed recently, e.g. \citep{LeTrieuKurosawaOgata2009b,SchuldtMatsuura2010}, but also serve for analyzing the early schemes that have a speculative security.<br/> The contents of this talk are parts of the speaker's PhD thesis.
Prochains exposés
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La crypto-graphie et les crypto-monnaies
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SoK: Security of the Ascon Modes
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The Ascon authenticated encryption scheme and hash function of Dobraunig et al (Journal of Cryptology 2021) were recently selected as winner of the NIST lightweight cryptography competition. The mode underlying Ascon authenticated encryption (Ascon-AE) resembles ideas of SpongeWrap, but not quite, and various works have investigated the generic security of Ascon-AE, all covering different attack[…] -
Comprehensive Modelling of Power Noise via Gaussian Processes with Applications to True Random Number Generators
Orateur : Maciej Skorski - Laboratoire Hubert Curien
The talk examines power noise modelling through Gaussian Processes for secure True Random Number Generators. While revisiting one-sided fractional Brownian motion, we obtain novel contributions by quantifying posterior uncertainty in exact analytical form, establishing quasi-stationary properties, and developing rigorous time-frequency analysis. These results are applied to model oscillator[…]-
Cryptography
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TRNG
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CryptoVerif: a computationally-sound security protocol verifier
Orateur : Bruno Blanchet - Inria
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Cryptography
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