On Round-Efficient Non-Malleable Protocols

The round complexity of non-malleable commitments and non-malleable zero knowledge arguments has been an open question for long time. Very recent results of Pass [TCC 2013] and of Goyal et al. [FOCS 2014, STOC 2016], gave almost definitive answers. In this work we show how to construct round-efficient non-malleable protocols via compilers. Starting from protocols enjoying limited non-malleability features, our compilers obtain fullfledged non-malleability without penalizing the round complexity. By instantiating our compilers with known candidate constructions, the resulting schemes improve the current state of the art in light of subtleties that revisit the analysis of previous work. Additionally, our compilers give a non-malleable zero-knowledge argument of knowledge that features delayed-input completeness. This property is satisfied by the proof of knowledge of Lapidot and Shamir [CRYPTO 1990] and has recently been used to improve the round complexity of several cryptographic protocols.