This paper addresses the challenges of key security protection in the two-party collaborative governance process within blockchain systems by proposing a two-party collaborative signature scheme based on the domestically developed commercial cryptographic algorithm SM2. Although traditional SM2 signatures implemented in software are susceptible to attacks that can lead to key leakage, hardware protection, although feasible, is not suitable for blockchain application scenarios. To overcome these limitations, this study combines zero-knowledge proof and homomorphic encryption technologies to introduce a homomorphic encryption-based two-party multiplication-addition converter (MtoA) design. This enables the realization of a two-party SM2 signature scheme that effectively resolves issues related to the easy leakage of signing private keys and the excessive concentration of the signing authority. In the proposed scheme, multiplication and addition operations are performed through precomputation, resulting in high signature efficiency. Furthermore, the scheme is proven to be secure within a hybrid model under a universally composable framework. The experimental results indicate that the proposed scheme offers advantages in both collaborative signature execution efficiency and bandwidth requirements while ensuring key security. This makes it suitable for practical applications in two-party collaborative governance within blockchain environments. The research presented in this paper provides an effective solution for key security in blockchain two-party collaborative governance, complies with national cryptographic standards, and holds significant application value.