Paper 2020/023

Threshold Multi-Signature with an Offline Recovery Party

Riccardo Longo and Alessio Meneghetti and Massimiliano Sala

Abstract

Key custody is a sensitive aspect of cryptocurrencies. The employment of a custodian service together with threshold-multi-party signatures helps to manage secret keys more safely and effectively, e.g. allowing the recovery of crypto-assets when users lose their own keys. Advancing from a protocol by Gennaro et al. we propose a protocol with two main properties. First it allows the recovery party to remain offline during the enrollment of any user, solving a real-life problem of maintaining online only one trusted third party. Second our multi-party signature is compatible with a deterministic derivation of public and private keys.