Digital signatures
To authenticate the identity of the sender
To ensure the original content of e-message is unchanged
Digital certificates and Certificate Authorities (CAs)
They verify that the holder of a public and/or private key is who they claim to be
Third parties called certificate authorities (CAs) issue digital certificates that contain things such as the holder’s name, validity period, public key information, and a signed hash of the certificate data
Example: the third-party CAs: Verisign.com