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**2020/162**

**Title:**

A Secret-Sharing Based MPC Protocol for Boolean Circuits with Good Amortized Complexity

**Authors:**
Ignacio Cascudo, Jaron Skovsted Gundersen

**Abstract:**

We present a new secure multiparty computation protocol in the preprocessing model that allows for the evaluation of a number of instances of a boolean circuit in parallel, with a small online communication complexity per instance of 10 bits per party and multiplication gate. Our protocol is secure against an active dishonest majority, and can be also transformed, via known techniques, into a protocol for the evaluation of a single “well-formed” boolean circuit with the same complexity per multiplication gate at the cost of some overhead that depends on the topology of the circuit. Our protocol uses an approach introduced recently in the setting of honest majority and information-theoretical security which, using an algebraic notion called reverse multiplication friendly embeddings, essentially transforms a batch of evaluations of an arithmetic circuit over a small field into one evaluation of another arithmetic circuit over a larger field. To obtain security against a dishonest majority we combine this approach with the well-known SPDZ protocol that operates over a large field. Structurally our protocol is most similar to MiniMAC, a protocol which bases its security on the use of error-correcting codes, but our protocol has a communication complexity which is half of that of MiniMAC when the best available binary codes are used. This makes it fully compatible with the technique from MiniMAC that allows to adapt the protocol for the computation of a well-formed boolean circuit. With respect to certain variant of MiniMAC that utilizes codes over large fields, our communication complexity is slightly worse; however, that variant of MiniMAC needs a much larger preprocessing than ours. We also show that our protocol also has smaller amortized communication complexity than Committed MPC, a protocol for general fields based on homomorphic commitments, if we use the best available constructions for those commitments. Finally, we construct a preprocessing phase from oblivious transfer based on ideas from MASCOT and Committed MPC.

**ePrint:**
https://eprint.iacr.org/2020/162

**Talk: **https://www.youtube.com/watch?v=lHC1ik8iTAU

**Slides: **https://iacr.org/submit/files/slides/2020/tcc/tcc2020/217/slides.pdf

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