Everyone has a variety of identification, such as ID card, driver's license, passport, etc. These certificates are stamped and certified by the corresponding issuing authority, which has high credibility and is difficult to forge. With the development of science and technology, you can also authenticate your identity through biometric features such as fingerprints and retina. Digital certificate, also known as electronic certificate, is similar to ID card in daily life, and it is also another form of identity authentication, which is used to identify users in the network. Digital certificate integrates a variety of encryption algorithms. The certificate itself has public key information, which can complete the corresponding encryption and decryption operations. At the same time, it also has a digital signature of its own information, which can identify the issuing authority of the certificate and the integrity of the certificate content. Because the certificate itself contains the user's authentication information, it can be used as the basis for user identification. Usually, a digital certificate will contain the following contents: the name of the object (person, server, organization); Expiration time of the certificate; The issuing authority of the certificate (who guarantees the certificate); The certificate information is digitally signed by the certificate issuing authority; Signature algorithm; The public key of the object. The name of the object refers to the user represented by the certificate, which can be an individual, a server, an organization, etc. The expiration time of the certificate is used to determine whether the certificate is still valid. The issuing authority will guarantee the authenticity and validity of the certificate and ensure that the information contained in the certificate is verified. Digital signature is used to identify the issuing authority of the certificate and whether the content of the certificate is complete. The issuing authority signs the certificate with the private key, and the verifier decrypts the signature with the public key of the issuing authority. By comparing with the abstract generated by the abstract algorithm, it can be verified whether the certificate is issued by the organization and whether the information is complete. Encrypt the information with the public key of the object, and transmit the information to the receiver, and the receiver will decrypt it with the private key corresponding to the public key.