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Prochain séminaire BlockSem avec Yannick Seurin (ANSSI) et Juan Garay (Texas A&M University)

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Le prochain séminaire Blocksem, dédié aux technologies blockchains, se tiendra le jeudi 22 novembre au centre de recherche Inria Saclay - Île-de-France (salle Gilles Kahn). Les intervenants de cette nouvelle session sont Yannick Seurin, de l'Agence nationale de la sécurité des systèmes d'information, et Juan Garay, de Texas A&M University.

  • Date : 22/11/2018
  • Lieu : Centre de recherche Inria Saclay - Île-de-France, Bâtiment Alan Turing, 1 rue Honoré d'Estienne d'Orves - 91120 Palaiseau (Salle Gilles Kahn)
  • Intervenant(s) : Juan Garay (Texas A&M University) & Yannick Seurin (Agence nationale de la sécurité des systèmes d'information)

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Programme du séminaire


Yannick Seurin, Agence nationale de la sécurité des systèmes d'information
More Schnorr Tricks for Bitcoin (résumé ci-après)


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Juan Garay, Texas A&M University
Foundational Aspects of Blockchain Protocols (résumé ci-après)

Résumés des exposés

Yannick Seurin, ANSSI
More Schnorr Tricks for Bitcoin
This will be a follow-up to the previous talk "Efficiency and Privacy Improvements for Bitcoin with Schnorr Signatures" from September 20. We will continue to explore the possibilities offered by the foreseen deployment of Schnorr signatures in Bitcoin. We will present three recent proposals building on Schnorr signatures:

  • Taproot, proposed by Greg Maxwell,
  • Scriptless scripts, proposed by Andrew Poelstra,
  • Discreet Log Contracts, proposed by Thaddeus Dryja.

Juan Garay, Texas A&M University
Foundational Aspects of Blockchain Protocols
Decentralized cryptocurrencies such as Bitcoin have ignited much excitement, not only for their novel realization of  central bank-free financial instruments, but also as an alternative approach to classical distributed computing problems, such as reaching agreement distributedly in the presence of misbehaving parties, as well as to numerous other applications - contracts, reputation systems, name services, etc. The soundness and security of these applications, however, hinge on the thorough understanding of the fundamental properties of their underlying blockchain data structure, which parties (“miners”) maintain and try to extend by generating proofs of various kinds, “proofs of work” (PoW, aka “cryptographic puzzle”) perhaps being the most interesting ones.
In this talk we formulate such fundamental properties of the blockchain - "common prefix," "chain quality," "chain growth" - and show how applications such as consensus and a robust public transaction ledger can be built "on top'' of them, assuming the adversary’s hashing power is strictly less than ½. The above properties hold assuming that all parties - honest and adversarial - ”wake up” and start computing at the same time, or, alternatively, that they compute on a common random string (the “genesis” block) only made available at the exact time when the protocol execution is to begin. We also address the question of whether such a trusted setup/behavioral assumption is necessary, answering it in the negative by presenting a Bitcoin-like blockchain protocol that is provably secure without trusted setup.  A direct consequence of this last construction is that consensus can be solved directly by a blockchain protocol without trusted setup assuming an honest majority (in terms of computational power), in contrast to what is shown in the classical distributed computing literature, an apparent contradiction that we also explain.
Most of this talk is based on joint work with Aggelos Kiayias (U. of Edinburgh), Nikos Leonardos (U. of Athens) and Giorgios Panagiotakos (U. of Edinburgh).

Le but des séminaires pluridisciplinaires BlockSem est de réunir les chercheurs et enseignants-chercheurs autour de la thématique des monnaies électroniques et des blockchains vues sous différents angles : algorithmique distribuée, cryptographie, modélisation économique, gouvernance et droit. Alors que beaucoup d'initiatives et d'applications se lancent dans les blockchains sans bases claires, ce séminaire - organisé par le centre de recherche Inria Saclay - Île-de-France et le laboratoire d’informatique de l’École polytechnique / CNRS (LIX) - se veut très académique et avancé pour permettre d’étudier les fondements de ces nouveaux objets informatiques.

Mots-clés : École polytechnique Inria Saclay - Île-de-France LIX Blockchain Séminaire BlockSem

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