Gadgets for Threshold AES: Correlation Robust Hash and Authenticated Garbling

Abstract. In this talk, we present two gadgets in general-purpose MPC for threshold symmetric-key primitives: correlation robust hash functions for better concrete security and authenticated garbling schemes for better concrete efficiency. Firstly, we show the construction of a tweakable circular correlation robust hash (TCCRH) function with high concrete security. It is useful in popular garbling schemes and also for converting correlated OT to standard OT. We show an efficient instantiation of TCCRH based solely on AES modeled as an ideal cipher. The integration of TCCRH and half-gates garbling achieves optimal security. Secondly, we introduce the basic authenticated garbling gadget and explain how it enables active security without relying on generic and “heavy” machinery like cut-and-choose. We also briefly mention our recent progress that further improves the asymptotic efficiency of this gadget, bringing communication close to its semi-honest counterpart.

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