Abstract: In digital signature algorithms,if the private signing key is leaked,an adversary can arbitrarily forge the signature of a legitimate user,thereby infringing upon the legitimate user’s rights and interests.Two-party threshold signature splits the private signing key into two parts,with each of the two signature participants holding one part and collaboratively generating the digital signature,which effectively enhances the security of the scheme.This paper proposes a new two-party threshold signature algorithm for the domestic SM2 signature algorithm.The new algorithm divides the two-party signature generation process into an offline phase thatdoes not require the message to be signed and an online phase that requires the message to be signed.It applies the existing MtA(Multiplicative-to-Additive) protocol once in the offline phase,thereby achieving high efficiency in the online phase.Analysis and verification show that,compared with other SM2 two-party signature schemes,the proposed scheme only needs to perform simple integer addition,multiplication,and modulo operations in the online phase of collaborative signature,it features extremely high efficiency and extremely low computational overhead,thus exhibiting significant advantages such as high collaborative signature operation efficiency and low bandwidth requirements in all scenarios,especially in low-latency scenarios.

Key words: SM2, Two-party threshold signature, Domestic cryptographic, Homomorphic encryption, Multiplicative-to-Additive protocol