[Resource Topic] 2017/931: Delayed-Input Non-Malleable Zero Knowledge and Multi-Party Coin Tossing in Four Rounds

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Delayed-Input Non-Malleable Zero Knowledge and Multi-Party Coin Tossing in Four Rounds

Authors: Michele Ciampi, Rafail Ostrovsky, Luisa Siniscalchi, Ivan Visconti


In this work we start from the following two results in the state-of-the art: 1) 4-round non-malleable zero knowledge (NMZK): Goyal et al. in FOCS 2014 showed the first 4-round one-one NMZK argument from one-way functions (OWFs). Their construction requires the prover to know the instance and the witness already at the 2nd round. 2) 4-round multi-party coin tossing (MPCT): Garg et al. in Eurocrypt 2016 showed the first 4-round protocol for MPCT. Their result crucially relies on 3-round 3-robust parallel non-malleable commitments. So far there is no candidate construction for such a commitment scheme under standard polynomial-time hardness assumptions. We improve the state-of-the art on NMZK and MPCT by presenting the following two results: 1) a delayed-input 4-round one-many NMZK argument \Pi_{nmzk} from OWFs; moreover \Pi_{nmzk} is also a delayed-input many-many synchronous NMZK argument. 2) a 4-round MPCT protocol \Pi_{mpcf} from one-to-one OWFs; \Pi_{mpcf} uses \Pi_{nmzk} as subprotocol and exploits the special properties (e.g., delayed input, many-many synchronous) of \Pi_{nmzk}. \Pi_{mpcf} makes use of a special proof of knowledge that offers additional security guarantees when played in parallel with other protocols. The new technique behind such a proof of knowledge is an additional contribution of this work and is of independent interest.

ePrint: https://eprint.iacr.org/2017/931

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