DualMS: Efficient Lattice-Based Two-Round Multi-Signature with Trapdoor-Free Simulation∗

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˚ard, Orlandi, Takahashi, and Tibouchi (PKC’21) and MuSig-L by

Boschini, Takahashi, and Tibouchi (CRYPTO’22).

In this work, we propose a 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 identical the normal signing procedure

and does not use lattice trapdoors like DOTT and MuSig-L.

Keywords. Multi-signature, Dilithium, Fiat-Shamir with aborts, Lattice, Post-quantum