1. Certificate Authority (CA): The entity responsible for issuing and revoking digital certificates. 2. Registration Authority (RA): Verifies the identity of entities requesting digital certificates. 3. Central Directory: A secure location for storing and managing certificates and keys. 4. Certificate Management System: Manages the lifecycle of certificates, including issuance, renewal, and revocation. 5. Client Software: Used by end-users to manage their keys and certificates.