A Certificate Authority (CA) is an entity that issues digital certificates, which are used to verify the identity of a user or organization. A digital certificate is an electronic document that contains the public key of an entity, along with other information such as the identity of the entity, the digital signature of the CA, and the period of validity.
For example, VeriSign is a popular certificate authority that issues digital certificates for websites. VeriSign’s digital certificates are used to verify the identity of the website and to encrypt the data sent between the website and the user’s browser.