Round-Optimal Threshold Blind Signature from Lattices

Blind signatures are crucial components in many privacy-preserving protocols in which the user will generate a signature on a message chosen by the user without revealing the message. The user is not able to generate more signatures than the number of queries it has made to the signer. Threshold signatures are another important component for privacy-preserving protocols, in which the signer is divided into many partial signers where every partial signer obtains a partial signing key derived from the master signing key. The resulting signature on a message can be generated only after a quorum of signers that includes at least a threshold of t signers jointly sign a message. In this work, we propose the first round-optimal lattice-based threshold blind signature scheme in the random oracle model (ROM). We prove that the one-more unforgeability of our scheme can be reduced to the one-wayness of partial lattice trapdoors introduced in [Albrecht et al. AsiaCrypt’25], which relies on the \(\kappa \) -MSIS (implied by the standard MSIS). In addition, we prove that our scheme satisfies malicious signer blindness under the standard MLWE assumption.