Cryptology ePrint Archive: Report 2020/1197

Black-Box Non-Interactive Non-Malleable Commitments

Rachit Garg and Dakshita Khurana and George Lu and Brent Waters

Abstract: There has been recent exciting progress on building non-interactive non-malleable commitments from judicious assumptions. All proposed approaches proceed in two steps. First, obtain simple "base'' commitment schemes for very small tag/identity spaces based on a various sub-exponential hardness assumptions. Next, assuming sub-exponential non-interactive witness indistinguishable proofs (NIWIs), and variants of keyless collision resistant hash functions, construct non-interactive compilers that convert tag-based non-malleable commitments for a small tag space into tag-based non-malleable commitments for a larger tag space. We propose the first black-box construction of non-interactive non-malleable commitments. Our key technical contribution is a novel way of implementing the non-interactive proof of consistency required by the tag amplification process. Prior to our work, the only known approach to tag amplification without setup and with black-box use of the base scheme (Goyal, Lee, Ostrovsky and Visconti, FOCS 2012) added multiple rounds of interaction. Our construction satisfies the strongest known definition of non-malleability, i.e., CCA (chosen commitment attack) security. In addition to being black-box, our approach dispenses with the need for sub-exponential NIWIs, that was common to all prior work. Instead of NIWIs, we rely on sub-exponential hinting PRGs which can be obtained based on a broad set of assumptions such as sub-exponential CDH or LWE.

Category / Keywords: cryptographic protocols / non malleable commitments, non-interactive

Date: received 1 Oct 2020

Contact author: rachit0596 at gmail com, dakshkhurana@gmail com, georgelu97@gmail com, bwaters@cs utexas edu

Available format(s): PDF | BibTeX Citation

Version: 20201006:093246 (All versions of this report)

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