A certificate is an attestation that a particular Public Key belongs to a particular person, company or entity. They are meant to help discourage someone from using a counterfeit key in order to impersonate someone else. A certificates commonly contains the name of a person, company or entity as well as the public key associated with them and information about the organization that issued the certificate. The whole certificate itself is then digitally signed by the certificate issuer to prove that it is genuine and has not been altered by anyone else.

Examples of popular certificate issuers are VeriSign and Thawte.