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  • Author: Peeter Laud x
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Parallel Oblivious Array Access for Secure Multiparty Computation and Privacy-Preserving Minimum Spanning Trees

Abstract

In this paper, we describe efficient protocols to perform in parallel many reads and writes in private arrays according to private indices. The protocol is implemented on top of the Arithmetic Black Box (ABB) and can be freely composed to build larger privacypreserving applications. For a large class of secure multiparty computation (SMC) protocols, our technique has better practical and asymptotic performance than any previous ORAM technique that has been adapted for use in SMC.

Our ORAM technique opens up a large class of parallel algorithms for adoption to run on SMC platforms. In this paper, we demonstrate how the minimum spanning tree (MST) finding algorithm by Awerbuch and Shiloach can be executed without revealing any details about the underlying graph (beside its size). The data accesses of this algorithm heavily depend on the location and weight of edges (which are private) and our ORAM technique is instrumental in their execution. Our implementation is the first-ever realization of a privacypreserving MST algorithm with sublinear round complexity.

Open access
Preprocessing Based Verification of Multiparty Protocols with Honest Majority

Abstract

This paper presents a generic “GMW-style” method for turning passively secure protocols into protocols secure against covert attacks, adding relatively cheap offline preprocessing and post-execution verification phases. Our construction performs best with a small number of parties, and its main benefit is the total cost of the online and the offline phases. In the preprocessing phase, each party generates and shares a sufficient amount of verified multiplication triples that will be later used to assist that party’s proof. The execution phase, after which the computed result is already available to the parties, has only negligible overhead that comes from signatures on sent messages. In the postprocessing phase, the verifiers repeat the computation of the prover in secret-shared manner, checking that they obtain the same messages that the prover sent out during execution. The verification preserves the privacy guarantees of the original protocol. It is applicable to protocols doing computations over finite rings, even if the same protocol performs its computation over several distinct rings. We apply our verification method to the Sharemind platform for secure multiparty computations (SMC), evaluate its performance and compare it to other existing SMC platforms offering security against stronger than passive attackers.

Open access