Cryptology ePrint Archive: Report 2019/017

CHURP: Dynamic-Committee Proactive Secret Sharing

Sai Krishna Deepak Maram and Fan Zhang and Lun Wang and Andrew Low and Yupeng Zhang and Ari Juels and Dawn Song

Abstract: We introduce CHURP (CHUrn-Robust Proactive secret sharing). CHURP enables secure secret-sharing in dynamic settings, where the committee of nodes storing a secret changes over time. Designed for blockchains, CHURP has lower communication complexity than previous schemes: $O(n)$ on-chain and $O(n^2)$ off-chain in the optimistic case of no node failures.

CHURP includes several technical innovations: An efficient new proactivization scheme of independent interest, a technique (using asymmetric bivariate polynomials) for efficiently changing secret-sharing thresholds, and a hedge against setup failures in an efficient polynomial commitment scheme. We also introduce a general new technique for inexpensive off-chain communication across the peer-to-peer networks of permissionless blockchains.

We formally prove the security of CHURP, report on an implementation, and present performance measurements.

Category / Keywords: cryptographic protocols / secret sharing, threshold cryptography, blockchains

Date: received 6 Jan 2019, last revised 16 May 2019

Contact author: sm2686 at cornell edu

Available format(s): PDF | BibTeX Citation

Note: Clarified communication model differences between different paths of CHURP.

Version: 20190516:160237 (All versions of this report)

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