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Universally Composable Almost-Everywhere Secure Computation

Authors: Nishanth Chandran, Pouyan Forghani, Juan Garay, Rafail Ostrovsky, Rutvik Patel, and Vassilis Zikas

Published in: LIPIcs, Volume 230, 3rd Conference on Information-Theoretic Cryptography (ITC 2022)

Most existing work on secure multi-party computation (MPC) ignores a key idiosyncrasy of modern communication networks, that there are a limited number of communication paths between any two nodes, many of which might even be corrupted. The problem becomes particularly acute in the information-theoretic setting, where the lack of trusted setups (and the cryptographic primitives they enable) makes communication over sparse networks more challenging. The work by Garay and Ostrovsky [EUROCRYPT'08] on almost-everywhere MPC (AE-MPC), introduced "best-possible security" properties for MPC over such incomplete networks, where necessarily some of the honest parties may be excluded from the computation. In this work, we provide a universally composable definition of almost-everywhere security, which allows us to automatically and accurately capture the guarantees of AE-MPC (as well as AE-communication, the analogous "best-possible security" version of secure communication) in the Universal Composability (UC) framework of Canetti. Our results offer the first simulation-based treatment of this important but under-investigated problem, along with the first simulation-based proof of AE-MPC. To achieve that goal, we state and prove a general composition theorem, which makes precise the level or "quality" of AE-security that is obtained when a protocol’s hybrids are replaced with almost-everywhere components.

Cite as

Nishanth Chandran, Pouyan Forghani, Juan Garay, Rafail Ostrovsky, Rutvik Patel, and Vassilis Zikas. Universally Composable Almost-Everywhere Secure Computation. In 3rd Conference on Information-Theoretic Cryptography (ITC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 230, pp. 14:1-14:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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  author =	{Chandran, Nishanth and Forghani, Pouyan and Garay, Juan and Ostrovsky, Rafail and Patel, Rutvik and Zikas, Vassilis},
  title =	{{Universally Composable Almost-Everywhere Secure Computation}},
  booktitle =	{3rd Conference on Information-Theoretic Cryptography (ITC 2022)},
  pages =	{14:1--14:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-238-9},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{230},
  editor =	{Dachman-Soled, Dana},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{},
  URN =		{urn:nbn:de:0030-drops-164929},
  doi =		{10.4230/LIPIcs.ITC.2022.14},
  annote =	{Keywords: Secure multi-party computation, universal composability, almost-everywhere secure computation, sparse graphs, secure message transmission}
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