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Blockchain

Next BlockSem seminar with Yannick Seurin (ANSSI) and Juan Garay (Texas A&M University)

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The next Blocksem seminar, dedicated to Blockchain technologies, will be held on Thursday 22 November at the Inria Saclay Research Centre - Île-de-France (Gilles Kahn room). The speakers for this new session are Yannick Seurin, from the Agence nationale de la sécurité des systèmes d'information , and Juan Garay, from Texas A&M University.

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

Registration is mandatory. To do this, click here

Programme du séminaire

10.30 am

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

12.00 pm

Meals in the lobby of the building
If you do not have a catering badge, please register here to pick up your meal

1.30 pm

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

  

Abstracts

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).
 

The aim of the BlockSem multidisciplinary seminars is to bring together researchers and teacher-researchers around the theme of electronic currencies and blockchains from different angles : distributed algorithms, cryptography, economic modelling, governance and law. While many initiatives and applications are launching into blockchains without a clear basis, this seminar - organized by the Inria Saclay research centre - Île-de-France and the computer laboratory of the École polytechnique / CNRS (LIX) - is very academic and advanced to allow the foundations of these new computer objects to be studied.

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

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