Trout: Two-Round Threshold ECDSA from Class Groups

We present Trout (Two-ROUnd Threshold), the first distributed two-round ECDSA signing protocol for arbitrary thresholds. Trout has constant upload bandwidth per-party and processing time linear in the amount of participants. Moreover, Trout achieves the Identifiable Abort (IA) property, which means that if the protocol cannot terminate due to a failure, parties can attribute the failure to a specific party. We achieve this without a trusted setup.