Paper 2021/060 Original: eprint.iacr.org/2021/060 ↗

UC Non-Interactive, Proactive, Threshold ECDSA with Identifiable Aborts

Abstract

We present a distributed ECDSA protocol, for any number of signatories. The protocol improves on that of the authors (CCS'20), which in turn builds on the Gennaro & Goldfeder and Lindell & Nof protocols (CCS '18). Specifically: ** Only the last round of the protocol requires knowledge of the message, and the other rounds can take place in a preprocessing stage, lending to a non-interactive threshold ECDSA protocol. ** The protocol withstands adaptive corruption of signatories. Furthermore, it includes a periodic refresh mechanism and guarantees proactive security. ** The protocol achieves accountability by identifying corrupted signatories in case of failure to generate a valid signature. (Identifiable abort) Furthermore, we formulate a distributed signature ideal functionality within the UC framework that guarantees unforgeability, proactive security, and identifiable abort, and show that the protocol realizes this functionality in the global random oracle model, assuming Strong RSA, DDH, semantic security of the Paillier encryption, and a somewhat enhanced variant of existential unforgeability of ECDSA. This combination of properties (low latency, compatibility with cold-wallet architectures, proactive security, identifiable abort and universally composable security) make our protocol a good fit for threshold wallets for ECDSA-based cryptocurrencies.