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

SPDZ (pronounced “Speedz”) is the nickname of the MPC protocol of Damg˚ard et al. from Crypto 2012. SPDZ provided various efficiency innovations on both the theoretical and practical sides compared to previous work in the preprocessing model. 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. In prior work this was assumed to be provided by a given setup functionality. Protocols for generating such shared BGV secret keys are likely to be of wider applicability than to the SPDZ protocol alone. 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. We also build a new online phase, which solves a major problem of the S...

• Type: Journal
• Year: 2013
• Where: ESORICS
• Authors: Ivan Damgård, Marcel Keller, Enrique Larraia, Valerio Pastro, Peter Scholl, Nigel P. Smart
• Keywords: ESORICS 2013, Security Privacy