Trout++: Robust Asynchronous Two-Round ECDSA for Arbitrary Thresholds

“Preview Talk” (by Team Trout) @ TCPT2, in reply to the NIST Threshold Call

Abstract: In this talk, we will present Trout++, a two-round threshold ECDSA signing protocol which may be used to achieve a robust, asynchronous protocol for arbitrary thresholds. Our protocol works with no additional prior setup/secure storage, offers a prover with complexity independent to the signing set, and avoids the complexity of the Asynchronous Common Subset problem via the extremely straightforward, yet still efficient, ROAST transformation. Our focus with Trout++ has been an exceptionally practical scheme, with comprehensive coverage of the concerns which are raised when actually deploying a threshold signature scheme, as we will discuss in this talk. We will also discuss our planned future work to ensure Trout++ is a leading candidate for standardization.

Joint work: Luke Parker, Hila Dahari-Garbian, Ariel Nof

[Slides] Suggested readings:

• Preview Writeup (PDF): Trout++: Two-Round Threshold ECDSA Composable with ROAST
• Trout: Two-Round Threshold ECDSA from Class Groups (ia.cr/2025/1666)
• Linearly Homomorphic Encryption from DDH (ia.cr/2015/047)