Cryptology ePrint Archive: Report 2019/253

Founding Secure Computation on Blockchains

Arka Rai Choudhuri and 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.

Category / Keywords: cryptographic protocols /

Original Publication (with major differences): IACR-EUROCRYPT-2019

Date: received 28 Feb 2019

Contact author: achoud at cs jhu edu,goyal@cs cmu edu,abhishek@cs jhu edu

Available format(s): PDF | BibTeX Citation

Version: 20190228:204310 (All versions of this report)

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