Paper 2025/240

Robust Non-Interactive Zero-Knowledge Combiners

Abstract

A $t$-out-of-$n$ robust non-interactive zero-knowledge (NIZK) combiner is a construction that, given access to $n$ candidate instantiations of a NIZK for some language, itself implements a NIZK for the same language. Moreover, the combiner is secure, assuming at least $$ of the given candidates are secure. In this work, we provide the first definition of combiners for NIZK, and prove that no robust NIZK combiner exists assuming $$ (unless the polynomial hierarchy collapses). On the positive side, we provide different constructions of robust NIZK combiners for $$. In particular, we show how to obtain: 1) A black-box combiner working for a special class of {\em homomorphic} languages where $$ are polynomial and $$. 2) A non-black-box combiner working for any language, where $$ are constant and $$. 3) A non-black-box combiner working for any language, where $$ are polynomial and $$.