Threshold ECDSA with an Offline Recovery Party
This addresses the need for secure distributed signing in scenarios like cryptocurrency wallets where participants may be offline, offering an incremental improvement over existing threshold schemes.
The paper tackles the problem of enabling threshold ECDSA signatures with an offline participant during key generation, presenting a protocol that achieves this without a trusted third party and proves security against adaptive malicious adversaries.
A $(t,n)-$ threshold signature scheme enables distributed signing among $n$ players such that any subgroup of size $t$ can sign, whereas any group with fewer players cannot. Our goal is to produce signatures that are compatible with an existing centralized signature scheme: the key generation and signature algorithm are replaced by a communication protocol between the parties, but the verification algorithm remains identical to that of a signature issued using the centralized algorithm. Starting from the threshold schemes for the ECDSA signature due to R. Gennaro and S. Goldfeder, we present the first protocol that supports multiparty signatures with an offline participant during the Key Generation Phase, without relying on a trusted third party. Following well-established approaches, we prove our scheme secure against adaptive malicious adversaries.