Abstract: Aimed at the problem of private key protection in the open environment of existing terminals, a cooperative signature and cooperative decryption scheme C-SM2 is designed based on the standard SM2 cryptographic algorithm. Both parties independently generated the child private key, and cooperated to generate the public key. When the private key signature or decryption operation was performed on the data, both parties needed to cooperate to complete the operation. Neither party could obtain the complete private key, and thus could not forge the signature or decrypt the data, which fully ensured the security of the SM2 algorithm in the open environment. The scheme was applicable to protect the storage security and operation security of SM2 private key in the software cryptographic module, and was also applicable to other scenarios requiring collaborative signature and collaborative operation.