Digital signature is an electronic password composed of a series of symbols and codes generated by public key cryptography and other cryptographic algorithms, which is used to replace handwritten signatures and seals. This kind of electronic signature can also be technically verified, and its verification accuracy is incomparable with manual signature and physical drawings. This signature method can be used for authentication in a large number of trusted PKI domains or cross authentication in multiple trusted PKI domains, especially for security authentication and transmission on the Internet and WAN.