Best of Both Worlds: Revisiting the Spymasters Double Agent Problem

Anasuya Acharya, Carmit Hazay, Oxana Poburinnaya, Muthuramakrishnan Venkitasubramaniam

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

Abstract

This work introduces the notion of secure multiparty computation: MPC with fall-back security. Fall-back security for an n-party protocol is defined with respect to an adversary structure Z wherein security is guaranteed in the presence of both a computationally unbounded adversary with adversary structure Z, and a computationally bounded adversary corrupting an arbitrarily large subset of the parties. This notion was considered in the work of Chaum (Crypto 89) via the Spymaster’s double agent problem where he showed a semi-honest secure protocol for the honest majority adversary structure. Our first main result is a compiler that can transform any n-party protocol that is semi-honestly secure with statistical security tolerating an adversary structure Z to one that (additionally) provides semi-honest fall-back security w.r.t Z. The resulting protocol has optimal round complexity, up to a constant factor, and is optimal in assumptions and the adversary structure. Our second result fully characterizes when malicious fall-back security is feasible. More precisely, we show that malicious fallback secure protocol w.r.t Z exists if and only if Z admits unconditional MPC against a semi-honest adversary (namely, iff Z∈ Q2 ).

Original languageEnglish
Title of host publicationAdvances in Cryptology – CRYPTO 2023 - 43rd Annual International Cryptology Conference, CRYPTO 2023, Proceedings
EditorsHelena Handschuh, Anna Lysyanskaya
PublisherSpringer Science and Business Media Deutschland GmbH
Pages328-359
Number of pages32
ISBN (Print)9783031385568
DOIs
StatePublished - 2023
EventAdvances in Cryptology – CRYPTO 2023 - 43rd Annual International Cryptology Conference, CRYPTO 2023, Proceedings - Santa Barbara, United States
Duration: 20 Aug 202324 Aug 2023

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume14081 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349

Conference

ConferenceAdvances in Cryptology – CRYPTO 2023 - 43rd Annual International Cryptology Conference, CRYPTO 2023, Proceedings
Country/TerritoryUnited States
CitySanta Barbara
Period20/08/2324/08/23

Bibliographical note

Publisher Copyright:
© 2023, International Association for Cryptologic Research.

Keywords

  • Best of Both Worlds
  • MPC Protocols Compiler
  • MPC with Fall-back Security

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