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IOS Press eBooks

Verifiable Computation in Multiparty Protocols with Honest Majority

Alisa Pankova, Peeter Laud

Published Jan 1, 2015• 0 citations
Publisher

Abstract

We present a generic method for turning passively secure protocols into protocols secure against covert attacks. This method adds to the protocol a post-execution verification phase that allows a misbehaving party to escape detection only with negligible probability. The execution phase, after which the computed protocol result is already available to the parties, has only negligible overhead added by our method.

DOI
10.3233/978-1-61499-532-6-165

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We present a generic method for turning passively secure protocols into protocols secure against covert attacks. This method adds to the protocol a post-execution verification phase that allows a misbehaving party to escape detection only with negligible probability. The execution phase, after which the computed protocol result is already available to the parties, has only negligible overhead added by our method.
Abstract. This paper presents a generic method for turning passively secure protocols into protocols secure against covert attacks, adding an offline preprocessing and a cheap post-execution verification phase. The execution phase, after which the computed result is already available to the parties, has only negligible overhead. Our method uses shared verification based on precomputed multiplica-tion triples. Such triples are often used to make the protocol execution itself faster, but in this work we make use of these triples especially for verification. The verification preserves the privacy guarantees of the original protocol, and it can be straightforwardly applied to protocols over finite rings, even if the same protocol performs its computation over several distinct rings at once.
Multiparty computation protocols (MPC) are said to be secure against covert adversaries if the honest parties are guaranteed to detect any misbehavior by the malicious parties with a constant probability. Protocols that, upon detecting a cheating attempt, additionally allow the honest parties to compute certificates, which enable third parties to be convinced of the malicious behavior of the accused parties, are called publicly verifiable. In this work, we make several contributions to the domain of MPC with security against covert adversaries. We identify a subtle flaw in a protocol of Goyal, Mohassel, and Smith (Eurocrypt 2008), meaning that their protocol does not allow to identify a cheating party, and show how to fix their original construction to obtain security against covert adversaries. We present generic compilers that transform arbitrary passively secure preprocessing protocols, i.e. protocols where the parties have no private inputs, into protocols that are secure against covert adversaries and publicly verifiable. Using our compiler, we construct the first efficient variants of the BMR and the SPDZ protocols that are secure and publicly verifiable against a covert adversary that corrupts all but one party, and also construct variants with covert security and identifiable abort. We observe that an existing impossibility result by Ishai, Ostrovsky, and Seyalioglu (TCC 2012) can be used to show that there exist certain functionalities that cannot be realized by parties, that have oracle-access to broadcast and arbitrary two-party functionalities, with information-theoretic security against a covert adversary.
We present improved protocols for the conversion of secret-shared bit-vectors into secret-shared integers and vice versa, for the use as subroutines in secure multiparty computation (SMC) protocols and for protocols verifying the adherence of parties to prescribed SMC protocols. The protocols are primarily designed for three-party computation with honest majority. We evaluate our protocols as part of the Sharemind three-party protocol set and see a general reduction of verification overheads, thereby increasing the practicality of covertly or actively secure Sharemind protocols.
We introduce the notion of covert security with public verifiability, building on the covert security model introduced by Aumann and Lindell (TCC 2007). Protocols that satisfy covert security guarantee that the honest parties involved in the protocol will notice any cheating attempt with some constant probability ɛ. The idea behind the model is that the fear of being caught cheating will be enough of a deterrent to prevent any cheating attempt. However, in the basic covert security model, the honest parties are not able to persuade any third party (say, a judge) that a cheating occurred. We propose (and formally define) an extension of the model where, when an honest party detects cheating, it also receives a certificate that can be published and used to persuade other parties, without revealing any information about the honest party’s input. In addition, malicious parties cannot create fake certificates in the attempt of framing innocents. Finally, we construct a secure two-party computation protocol for any functionality f that satisfies our definition, and our protocol is almost as efficient as the one of Aumann and Lindell. We believe that the fear of a public humiliation or even legal consequences vastly exceeds the
This work studies compilation of honest-majority semi-honest secure multi-party protocols secure up to additive attacks to maliciously secure computation with abort. Prior work concentrated on arithmetic circuits composed of addition and multiplication gates, while many practical protocols rely on additional types of elementary operations or gates to achieve good performance. In this work we revisit the notion of security up to additive attacks in the presence of additional gates such as random element generation and opening. This requires re-evaluation of functions that can be securely evaluated, extending the notion of protocols secure up to additive attacks, and re-visiting the notion of delayed verification that points to weaknesses in its prior use and designing a mitigation strategy. We transform the computation using dual execution to achieve security in the malicious model with abort and experimentally evaluate the difference in performance of semi-honest and malicious protocols to demonstrate the low cost.