What is an SSL certificate?

First of all, SSL (Secure Sockets Layer, Secure Sockets Layer) is a security protocol, the purpose is to provide security and data integrity guarantee for Internet communication. The SSL certificate follows the SSL protocol and can be installed on the server to encrypt data transmission.
CA (Digital Certificate Authority, Certificate Authority) is a third-party authority that undertakes public key legality verification. It is responsible for specifying policies and procedures to verify the identity of users, and signing SSL certificates to ensure the identity and integrity of the certificate holder. Ownership of the public key. The CA authority issues an SSL certificate for each user who uses the public key. The role of the SSL certificate is to prove that the individual/enterprise listed in the certificate legally owns the public key listed in the certificate. The digital signature of the CA makes it impossible for attackers to forge and tamper with the certificate.
The SSL certificate is actually the authentication of the user's public key by the CA, and the content includes the information of the electronic visa authority, public key user information, public key, the signature and validity period of the authority, etc.