Security Against Covert Adversaries: Efficient Protocols for Realistic Adversaries |
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Authors: | Yonatan Aumann Yehuda Lindell |
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Affiliation: | 1. Department of Computer Science, Bar-Ilan University, Ramat Gan, Israel
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Abstract: | In the setting of secure multiparty computation, a set of mutually distrustful parties wish to securely compute some joint
function of their private inputs. The computation should be carried out in a secure way, meaning that no coalition of corrupted
parties should be able to learn more than specified or somehow cause the result to be “incorrect.” Typically, corrupted parties
are either assumed to be semi-honest (meaning that they follow the protocol specification) or malicious (meaning that they
may deviate arbitrarily from the protocol). However, in many settings, the assumption regarding semi-honest behavior does
not suffice and security in the presence of malicious adversaries is excessive and expensive to achieve.
In this paper, we introduce the notion of covert adversaries, which we believe faithfully models the adversarial behavior in many commercial, political, and social settings. Covert adversaries
have the property that they may deviate arbitrarily from the protocol specification in an attempt to cheat, but do not wish
to be “caught” doing so. We provide a definition of security for covert adversaries and show that it is possible to obtain
highly efficient protocols that are secure against such adversaries. We stress that in our definition, we quantify over all
(possibly malicious) adversaries and do not assume that the adversary behaves in any particular way. Rather, we guarantee
that if an adversary deviates from the protocol in a way that would enable it to “cheat” (meaning that it can achieve something
that is impossible in an ideal model where a trusted party is used to compute the function), then the honest parties are guaranteed
to detect this cheating with good probability. We argue that this level of security is sufficient in many settings. |
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