Explanation:
Public key infrastructure (PKI) combines public key encryption with a trusted third party to publish and revoke digital certificates that contain the public key of the sender. Senders can digitally sign a message with their private key and attach their digital certificate (provided by the trusted third party). These characteristics allow senders to provide authentication, integrity validation and nonrepudiation. Symmetric cryptography provides confidentiality. Mashing can provide integrity and confidentiality. Message authentication codes provide integrity.