Final answer:
The entity used to issue and revoke certificates in a PKI is B) CA, which stands for Certificate Authority. It is a trusted entity responsible for managing digital certificates, whereas options like WPA, RADIUS, and Diffie-Hellman serve different purposes and are not involved with certificates in the context of PKI.
Step-by-step explanation:
To address the question of which of these is used to issue and revoke certificates in a PKI (Public Key Infrastructure), the correct answer is B) CA, which stands for Certificate Authority. A Certificate Authority is a trusted entity in a PKI that issues digital certificates to organizations or individuals after verifying their identity. It's also responsible for revoking certificates when needed, such as in the case of a security breach or when a certificate is no longer valid.
Other options provided, such as A) WPA (Wi-Fi Protected Access), C) RADIUS (Remote Authentication Dial-In User Service), and D) Diffie-Hellman, are not associated with the issuance and revocation of certificates. WPA is a security protocol for wireless networks, RADIUS is a networking protocol that provides centralized Authentication, Authorization, and Accounting management for users who connect and use a network service, and Diffie-Hellman is a method of securely exchanging cryptographic keys over a public channel.