A provable-secure and practical two-party distributed signing protocol for SM2 signature algorithm

Mobile devices are widely used for data access, communications and storage. However, storing a private key for signature and other cryptographic usage on a single mobile device can be challenging, due to its computational limitations. Thus, a number of (t, n) threshold secret sharing schemes designed to minimize private key from leakage have been proposed in the literature. However, existing schemes generally suffer from key reconstruction attack. In this paper, we propose an efficient and secure two-party distributed signing protocol for the SM2 signature algorithm. The latter has been mandated by the Chinese government for all electronic commerce applications. The proposed protocol separates the private key to storage on two devices and can generate a valid signature without the need to reconstruct the entire private key. We prove that our protocol is secure under nonstandard assumption. Then, we implement our protocol using MIRACL Cryptographic SDK to demonstrate that the protocol can be deployed in practice to prevent key disclosure.