Description
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, 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 report on the functionality and implementation of CHURP, and present performance improvements.