Enrique Larraia

Practical Covertly Secure MPC for Dishonest Majority – Or: Breaking the SPDZ Limits

SPDZ (pronounced “Speedz”) is the nickname of the MPC protocol of Damgard et al. from Crypto 2012. In this paper we both resolve a number of open problems with SPDZ; and present several theoretical and practical improvements to the protocol. In detail, we start by designing and implementing a covertly secure key generation protocol for obtaining a BGV public key and a shared associated secret key. We then construct both a covertly and actively secure preprocessing phase, both of which compare favourably with previous work in terms of efficiency and provable security.

Dishonest Majority Multi-Party Computation for Binary Circuits

We extend the Tiny-OT two party protocol of Nielsen et al (CRYPTO 2012) to the case of n parties in the dishonest majority setting. This is done by presenting a novel way of transferring pairwise authentications into global authentications. As a by product we obtain a more efficient manner of producing globally authenticated shares, in the random oracle model, which in turn leads to a more efficient two party protocol than that of Nielsen et al.

Implementing AES via an actively/covertly secure dishonest-majority MPC protocol

We describe an implementation of the protocol of Damgard, Pastro, Smart and Zakarias (SPDZ/Speedz) for multi-party computation in the presence of a dishonest majority of active adversaries. We present a number of modifications to the protocol; the first reduces the security to covert security, but produces significant performance enhancements; the second enables us to perform bit-wise operations in characteristic two fields. As a bench mark application we present the evaluation of the AES cipher, a now standard bench marking example for multi-party computation. We need examine two different implementation techniques, which are distinct from prior MPC work in this area due to the use of MACs within the SPDZ protocol. We then examine two implementation choices for the finite fields; one based on finite fields of size 28 and one based on embedding the AES field into a larger finite field of size 240.

Multilinear Maps from Obfuscation

We provide constructions of multilinear groups equipped with natural hard problems from indistinguishability obfuscation, homomorphic encryption, and NIZKs. This complements known results on the constructions of indistinguishability obfuscators from multilinear maps in the reverse direction. n nWe provide two distinct, but closely related constructions and show that multilinear analogues of the

Extending Oblivious Transfer Efficiently

mathrm {DDH}

High Performance Multi-Party Computation for Binary Circuits Based on Oblivious Transfer.

assumption hold for them. Our first construction is symmetric and comes with a

Multilinear Maps from Obfuscation.

kappa