International Association
for Cryptologic Research

A multi-signature scheme allows multiple signers to jointly sign a common message. In recent years, two lattice-based two-round multi-signature schemes based on Dilithium-G were proposed: DOTT by Damg{\aa}rd, Orlandi, Takahashi, and Tibouchi (PKC'21) and Musig-L by Boschini, Takahashi, and Tibouchi (CRYPTO'22). In this work, we propose a new lattice-based two-round multi-signature scheme called DualMS. Compared to DOTT, DualMS is likely to significantly reduce signature size, since it replaces an opening to a homomorphic trapdoor commitment with a Dilithium-G response in the signature. Compared to Musig-L, concrete parameters show that DualMS has smaller public keys, signatures, and lower communication, while the first round cannot be preprocessed offline as in Musig-L. The main reason behind such improvements is a trapdoor-free ``dual signing simulation'' of our scheme. Signature simulation of DualMS is virtually the same as the normal signing procedure and does not use lattice trapdoors like DOTT and Musig-L.