What security can we achieve within 4 rounds?

Carmit Hazay, Muthuramakrishnan Venkitasubramaniam

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

1 Scopus citations


Katz and Ostrovsky (Crypto 2004) proved that five rounds are necessary for stand-alone general black-box constructions of secure two-party protocols and at least four rounds are necessary if only one party needs to receive the output. Recently, Ostrovsky, Richelson and Scafuro (Crypto 2015) proved optimality of this result by showing how to realize arbitrary functionalities in four rounds where only one party receives the output via a black-box construction (and an extension to five rounds where both parties receive the output). In this paper we study the question of what security is achievable for stand-alone two-party protocols within four rounds. We first provide a four-round two-party protocol for coin-tossing that achieves 1/p-simulation security (i.e. simulation fails with probability at most 1/p+negl), in the presence of malicious corruptions. Next, we provide a four-round two-party protocol for general functionalities, where both parties receive the output, that achieves 1/p-security in the presence of malicious adversaries corrupting one of the parties, and full security in the presence of non-aborting malicious adversaries corrupting the other party. Next, we provide a three-round oblivious-transfer protocol, that achieves 1/p-simulation security against arbitrary malicious senders, while simultaneously guaranteeing a meaningful notion of privacy against malicious corruptions of either party. Finally, we show that the simulation-based security guarantees for our three-round protocols are optimal by proving that 1/p-simulation security is impossible to achieve against both parties in three rounds or less when requiring some minimal guarantees on the privacy of their inputs.

Original languageEnglish
Title of host publicationSecurity and Cryptography for Networks - 10th International Conference, SCN 2016, Proceedings
EditorsRoberto De Prisco, Vassilis Zikas
PublisherSpringer Verlag
Number of pages20
ISBN (Print)9783319446172
StatePublished - 2016
Event10th International Conference on Security and Cryptography for Networks, SCN 2016 - Amalfi, Italy
Duration: 31 Aug 20162 Sep 2016

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume9841 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference10th International Conference on Security and Cryptography for Networks, SCN 2016

Bibliographical note

Funding Information:
C. Hazay—Research partially supported by a grant from the Israel Ministry of Science and Technology (grant No. 3-10883), by the European Research Council under the ERC consolidators grant agreement n. 615172 (HIPS), and by the BIU Center for Research in Applied Cryptography and Cyber Security in conjunction with the Israel National Cyber Bureau in the Prime Minister’s Office.

Funding Information:
M. Venkitasubramaniam—Research supported by Google Faculty Research Grant and NSF Award CNS-1526377.

Publisher Copyright:
© Springer International Publishing Switzerland 2016.


  • Coin-tossing
  • Oblivious transfer
  • Round complexity
  • Secure computation


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