The client uses the CA certificate to authenticate the CA signature on the server certificate, as part of the authorizations before launching a secure connection.Usually, client software—for example, browsers—include a set of trusted CA certificates.Browsers and other clients of sorts characteristically allow users to add or do away with CA certificates at will.
The techniques used for domain validation vary between CAs, but in general domain validation techniques are meant to prove that the certificate applicant controls a given domain name, not any information about the applicant's identity.
Many Certificate Authorities also offer Extended Validation (EV) certificates as a more rigorous alternative to domain validated certificates.
The format of these certificates is specified by the X.509 standard.
One particularly common use for certificate authorities is to sign certificates used in HTTPS, the secure browsing protocol for the World Wide Web.
This is because many uses of digital certificates, such as for legally binding digital signatures, are linked to local law, regulations, and accreditation schemes for certificate authorities.
However, the market for globally trusted TLS/SSL server certificates is largely held by a small number of multinational companies.
In cryptography, a certificate authority or certification authority (CA) is an entity that issues digital certificates.
A digital certificate certifies the ownership of a public key by the named subject of the certificate.
This allows others (relying parties) to rely upon signatures or on assertions made about the private key that corresponds to the certified public key.