SSL/TLS certificates issued by a PKI enable encrypted communications, providing confidentiality and integrity, and also authenticate the server's identity. This ensures that clients are communicating with the genuine server and not an imposter. Self-signed certificates might offer encryption, but they do not provide third-party validation of server identity. SSH keys are used primarily for securing remote logins, not for encrypting web traffic. Symmetric key encryption does not provide authentication of the server to clients, as the same key is used for both encryption and decryption.