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Documents authored by Brassard, Gilles

Document
DOI: 10.4230/LIPIcs.TQC.2017.3
Provably Secure Key Establishment Against Quantum Adversaries

Authors: Aleksandrs Belovs, Gilles Brassard, Peter Høyer, Marc Kaplan, Sophie Laplante, and Louis Salvail

Published in: LIPIcs, Volume 73, 12th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2017)

Abstract
At Crypto 2011, some of us had proposed a family of cryptographic protocols for key establishment capable of protecting quantum and classical legitimate parties unconditionally against a quantum eavesdropper in the query complexity model. Unfortunately, our security proofs were unsatisfactory from a cryptographically meaningful perspective because they were sound only in a worst-case scenario. Here, we extend our results and prove that for any \eps > 0, there is a classical protocol that allows the legitimate parties to establish a common key after O(N) expected queries to a random oracle, yet any quantum eavesdropper will have a vanishing probability of learning their key after O(N^(1.5-\eps)) queries to the same oracle. The vanishing probability applies to a typical run of the protocol. If we allow the legitimate parties to use a quantum computer as well, their advantage over the quantum eavesdropper becomes arbitrarily close to the quadratic advantage that classical legitimate parties enjoyed over classical eavesdroppers in the seminal 1974 work of Ralph Merkle. Along the way, we develop new tools to give lower bounds on the number of quantum queries required to distinguish two probability distributions. This method in itself could have multiple applications in cryptography. We use it here to study average-case quantum query complexity, for which we develop a new composition theorem of independent interest.
Cite as

Aleksandrs Belovs, Gilles Brassard, Peter Høyer, Marc Kaplan, Sophie Laplante, and Louis Salvail. Provably Secure Key Establishment Against Quantum Adversaries. In 12th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 73, pp. 3:1-3:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{belovs_et_al:LIPIcs.TQC.2017.3,
  author =	{Belovs, Aleksandrs and Brassard, Gilles and H{\o}yer, Peter and Kaplan, Marc and Laplante, Sophie and Salvail, Louis},
  title =	{{Provably Secure Key Establishment Against Quantum Adversaries}},
  booktitle =	{12th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2017)},
  pages =	{3:1--3:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-034-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{73},
  editor =	{Wilde, Mark M.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2017.3},
  URN =		{urn:nbn:de:0030-drops-85816},
  doi =		{10.4230/LIPIcs.TQC.2017.3},
  annote =	{Keywords: Merkle puzzles, Key establishment schemes, Quantum cryptography, Adversary method, Average-case analysis}
}
Document
DOI: 10.4230/LIPIcs.TQC.2014.7
Exact Classical Simulation of the GHZ Distribution

Authors: Gilles Brassard, Luc Devroye, and Claude Gravel

Published in: LIPIcs, Volume 27, 9th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2014)

Abstract
John Bell has shown that the correlations entailed by quantum mechanics cannot be reproduced by a classical process involving non-communicating parties. But can they be simulated with the help of bounded communication? This problem has been studied for more than twenty years and it is now well understood in the case of bipartite entanglement. However, the issue was still widely open for multipartite entanglement, even for the simplest case, which is the tripartite Greenberger-Horne-Zeilinger (GHZ) state. We give an exact simulation of arbitrary independent von Neumann measurements on general n-partite GHZ states. Our protocol requires O(n^2) bits of expected communication between the parties, and O(n*log(n)) expected time is sufficient to carry it out in parallel. Furthermore, we need only an expectation of O(n) independent unbiased random bits, with no need for the generation of continuous real random variables nor prior shared random variables. In the case of equatorial measurements, we improve earlier results with a protocol that needs only O(n*log(n)) bits of communication and O(log^2(n)) parallel time. At the cost of a slight increase in the number of bits communicated, these tasks can be accomplished with a constant expected number of rounds.
Cite as

Gilles Brassard, Luc Devroye, and Claude Gravel. Exact Classical Simulation of the GHZ Distribution. In 9th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2014). Leibniz International Proceedings in Informatics (LIPIcs), Volume 27, pp. 7-23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@InProceedings{brassard_et_al:LIPIcs.TQC.2014.7,
  author =	{Brassard, Gilles and Devroye, Luc and Gravel, Claude},
  title =	{{Exact Classical Simulation of the GHZ Distribution}},
  booktitle =	{9th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2014)},
  pages =	{7--23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-73-6},
  ISSN =	{1868-8969},
  year =	{2014},
  volume =	{27},
  editor =	{Flammia, Steven T. and Harrow, Aram W.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2014.7},
  URN =		{urn:nbn:de:0030-drops-48025},
  doi =		{10.4230/LIPIcs.TQC.2014.7},
  annote =	{Keywords: Entanglement simulation, Greenberger-Horne-Zeilinger (GHZ) state, Multiparty entanglement, von Neumann's rejection algorithm, Knuth-Yao's sampling alg}
}
Document
DOI: 10.4230/DagSemRep.210
Quantum Algorithms (Dagstuhl Seminar 98191)

Authors: Thomas Beth and Gilles Brassard

Published in: Dagstuhl Seminar Reports. Dagstuhl Seminar Reports, Volume 1 (2021)

Abstract
Cite as

Thomas Beth and Gilles Brassard. Quantum Algorithms (Dagstuhl Seminar 98191). Dagstuhl Seminar Report 210, pp. 1-21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (1998)

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@TechReport{beth_et_al:DagSemRep.210,
  author =	{Beth, Thomas and Brassard, Gilles},
  title =	{{Quantum Algorithms (Dagstuhl Seminar 98191)}},
  pages =	{1--21},
  ISSN =	{1619-0203},
  year =	{1998},
  type = 	{Dagstuhl Seminar Report},
  number =	{210},
  institution =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemRep.210},
  URN =		{urn:nbn:de:0030-drops-150966},
  doi =		{10.4230/DagSemRep.210},
}
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