### Founding Secure Computation on Blockchains

Arka Rai Choudhuri, Vipul Goyal, and Abhishek Jain

##### Abstract

We study the foundations of secure computation in the blockchain-hybrid model, where a blockchain -- modeled as a global functionality -- is available as an Oracle to all the participants of a cryptographic protocol. We demonstrate both destructive and constructive applications of blockchains: - We show that classical rewinding-based simulation techniques used in many security proofs fail against blockchain-active adversaries that have read and post access to a global blockchain. In particular, we show that zero-knowledge (ZK) proofs with black-box simulation are impossible against blockchain-active adversaries. - Nevertheless, we show that achieving security against blockchain-active adversaries is possible if the honest parties are also blockchain active. We construct an $\omega(1)$-round ZK protocol with black-box simulation. We show that this result is tight by proving the impossibility of constant-round ZK with black-box simulation. - Finally, we demonstrate a novel application of blockchains to overcome the known impossibility results for concurrent secure computation in the plain model. We construct a concurrent self-composable secure computation protocol for general functionalities in the blockchain-hybrid model based on standard cryptographic assumptions. We develop a suite of techniques for constructing secure protocols in the blockchain-hybrid model that we hope will find applications to future research in this area.

Available format(s)
Category
Cryptographic protocols
Publication info
A major revision of an IACR publication in EUROCRYPT 2019
Contact author(s)
achoud @ cs jhu edu
goyal @ cs cmu edu
abhishek @ cs jhu edu
History
Short URL
https://ia.cr/2019/253

CC BY

BibTeX

@misc{cryptoeprint:2019/253,
author = {Arka Rai Choudhuri and Vipul Goyal and Abhishek Jain},
title = {Founding Secure Computation on Blockchains},
howpublished = {Cryptology ePrint Archive, Paper 2019/253},
year = {2019},
note = {\url{https://eprint.iacr.org/2019/253}},
url = {https://eprint.iacr.org/2019/253}
}

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