Tweed: Adaptively Secure Lattice-Based Two-Round Threshold Signatures

This paper gives the first lattice-based two-round threshold signature scheme that tolerates the adaptive corruption of up to $T -1$ out of $N$ signers. Our construction is based on the MLWE and MSIS assumptions. We substantially improve upon the only existing adaptively secure lattice-based construction, recently given by Katsumata, Reichle, and Takemure (CRYPTO '24), which requires five rounds.