3 Search Results for "Ando, Megumi"

Document
DOI: 10.4230/LIPIcs.ITC.2021.9
On the Complexity of Anonymous Communication Through Public Networks

Authors: Megumi Ando, Anna Lysyanskaya, and Eli Upfal

Published in: LIPIcs, Volume 199, 2nd Conference on Information-Theoretic Cryptography (ITC 2021)

Abstract
Onion routing is the most widely used approach to anonymous communication online. The idea is that Alice wraps her message to Bob in layers of encryption to form an "onion" and routes it through a series of intermediaries. Each intermediary’s job is to decrypt ("peel") the onion it receives to obtain instructions for where to send it next. The intuition is that, by the time it gets to Bob, the onion will have mixed with so many other onions that its origin will be hard to trace even for an adversary that observes the entire network and controls a fraction of the participants, possibly including Bob. Despite its widespread use in practice, until now no onion routing protocol was known that simultaneously achieved, in the presence of an active adversary that observes all network traffic and controls a constant fraction of the participants, (a) anonymity; (b) fault-tolerance, where even if a few of the onions are dropped, the protocol still delivers the rest; and (c) reasonable communication and computational complexity as a function of the security parameter and the number of participants. In this paper, we give the first onion routing protocol that meets these goals: our protocol (a) achieves anonymity; (b) tolerates a polylogarithmic (in the security parameter) number of dropped onions and still delivers the rest; and (c) requires a polylogarithmic number of rounds and a polylogarithmic number of onions sent per participant per round. We also show that to achieve anonymity in a fault-tolerant fashion via onion routing, this number of onions and rounds is necessary. Of independent interest, our analysis introduces two new security properties of onion routing - mixing and equalizing - and we show that together they imply anonymity.
Cite as

Megumi Ando, Anna Lysyanskaya, and Eli Upfal. On the Complexity of Anonymous Communication Through Public Networks. In 2nd Conference on Information-Theoretic Cryptography (ITC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 199, pp. 9:1-9:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{ando_et_al:LIPIcs.ITC.2021.9,
  author =	{Ando, Megumi and Lysyanskaya, Anna and Upfal, Eli},
  title =	{{On the Complexity of Anonymous Communication Through Public Networks}},
  booktitle =	{2nd Conference on Information-Theoretic Cryptography (ITC 2021)},
  pages =	{9:1--9:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-197-9},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{199},
  editor =	{Tessaro, Stefano},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ITC.2021.9},
  URN =		{urn:nbn:de:0030-drops-143282},
  doi =		{10.4230/LIPIcs.ITC.2021.9},
  annote =	{Keywords: Anonymity, privacy, onion routing}
}
Document
DOI: 10.4230/LIPIcs.ISAAC.2019.33
The I/O Complexity of Hybrid Algorithms for Square Matrix Multiplication

Authors: Lorenzo De Stefani

Published in: LIPIcs, Volume 149, 30th International Symposium on Algorithms and Computation (ISAAC 2019)

Abstract
Asymptotically tight lower bounds are derived for the I/O complexity of a general class of hybrid algorithms computing the product of n x n square matrices combining "Strassen-like" fast matrix multiplication approach with computational complexity Theta(n^{log_2 7}), and "standard" matrix multiplication algorithms with computational complexity Omega (n^3). We present a novel and tight Omega ((n/max{sqrt M, n_0})^{log_2 7}(max{1,(n_0)/M})^3M) lower bound for the I/O complexity of a class of "uniform, non-stationary" hybrid algorithms when executed in a two-level storage hierarchy with M words of fast memory, where n_0 denotes the threshold size of sub-problems which are computed using standard algorithms with algebraic complexity Omega (n^3). The lower bound is actually derived for the more general class of "non-uniform, non-stationary" hybrid algorithms which allow recursive calls to have a different structure, even when they refer to the multiplication of matrices of the same size and in the same recursive level, although the quantitative expressions become more involved. Our results are the first I/O lower bounds for these classes of hybrid algorithms. All presented lower bounds apply even if the recomputation of partial results is allowed and are asymptotically tight. The proof technique combines the analysis of the Grigoriev’s flow of the matrix multiplication function, combinatorial properties of the encoding functions used by fast Strassen-like algorithms, and an application of the Loomis-Whitney geometric theorem for the analysis of standard matrix multiplication algorithms. Extensions of the lower bounds for a parallel model with P processors are also discussed.
Cite as

Lorenzo De Stefani. The I/O Complexity of Hybrid Algorithms for Square Matrix Multiplication. In 30th International Symposium on Algorithms and Computation (ISAAC 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 149, pp. 33:1-33:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{destefani:LIPIcs.ISAAC.2019.33,
  author =	{De Stefani, Lorenzo},
  title =	{{The I/O Complexity of Hybrid Algorithms for Square Matrix Multiplication}},
  booktitle =	{30th International Symposium on Algorithms and Computation (ISAAC 2019)},
  pages =	{33:1--33:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-130-6},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{149},
  editor =	{Lu, Pinyan and Zhang, Guochuan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2019.33},
  URN =		{urn:nbn:de:0030-drops-115299},
  doi =		{10.4230/LIPIcs.ISAAC.2019.33},
  annote =	{Keywords: I/O complexity, Hybrid Algorithm, Matrix Multiplication, Recomputation}
}
Document
DOI: 10.4230/LIPIcs.ICALP.2018.144
Practical and Provably Secure Onion Routing

Authors: Megumi Ando, Anna Lysyanskaya, and Eli Upfal

Published in: LIPIcs, Volume 107, 45th International Colloquium on Automata, Languages, and Programming (ICALP 2018)

Abstract
In an onion routing protocol, messages travel through several intermediaries before arriving at their destinations; they are wrapped in layers of encryption (hence they are called "onions"). The goal is to make it hard to establish who sent the message. It is a practical and widespread tool for creating anonymous channels. For the standard adversary models - passive and active - we present practical and provably secure onion routing protocols. Akin to Tor, in our protocols each party independently chooses the routing paths for his onions. For security parameter lambda, our differentially private solution for the active adversary takes O(log^2 lambda) rounds and requires every participant to transmit O(log^{4} lambda) onions in every round.
Cite as

Megumi Ando, Anna Lysyanskaya, and Eli Upfal. Practical and Provably Secure Onion Routing. In 45th International Colloquium on Automata, Languages, and Programming (ICALP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 107, pp. 144:1-144:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

Copy BibTex To Clipboard

@InProceedings{ando_et_al:LIPIcs.ICALP.2018.144,
  author =	{Ando, Megumi and Lysyanskaya, Anna and Upfal, Eli},
  title =	{{Practical and Provably Secure Onion Routing}},
  booktitle =	{45th International Colloquium on Automata, Languages, and Programming (ICALP 2018)},
  pages =	{144:1--144:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-076-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{107},
  editor =	{Chatzigiannakis, Ioannis and Kaklamanis, Christos and Marx, D\'{a}niel and Sannella, Donald},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2018.144},
  URN =		{urn:nbn:de:0030-drops-91482},
  doi =		{10.4230/LIPIcs.ICALP.2018.144},
  annote =	{Keywords: Anonymity, traffic analysis, statistical privacy, differential privacy}
}
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