Optimization of 2-Party ECDSA Protocol

Jina Han, Yulim Shin, Hyung Tae Lee, Sungwook Kim

Abstract: 2-party ECDSA enables two parties to collaboratively generate signatures while keeping their signing key shares and the full signing key hidden throughout the process. With the rapid growth of blockchain and cryptocurrency systems, such protocols have become increasingly important for securing digital assets. A widely adopted design separates the signing phase into an offline phase for message-independent computations and an online phase for efficient signature generation. At ACM CCS 2021, Xue et al. proposed a two-party ECDSA protocol that requires only a single invocation of the Multiplicative-to-Additive (MtA) conversion in the offline phase and achieves optimality in the online phase. However, their key-resharing technique incurs additional computational and communication overhead. In this paper, we present a further optimization that bypasses key-resharing, hence leading to the elimination of redundant computational and communication costs. Excluding MtA, our protocol reduces elliptic curve scalar multiplications by four (a 25% reduction) and removes the transmission of one elliptic curve point and two field elements (a 27% reduction) compared with Xue et al. Our Rust implementation demonstrates that, although overall improvements are incremental once MtA costs are included, meaningful performance gains are observed, especially in signing time, when combined with a MtA based on oblivious transfer.

External IDs:dblp:journals/access/HanSLK25