What is a Public Key Infrastructure and what are its components?

A Public Key Infrastructure, or PKI, is the framework of policies, procedures, and technologies that manages digital certificates and public-private key pairs. Core components include the Certificate Authority, or CA, which issues and signs digital certificates; the Registration Authority, or RA, which verifies identity before certificate issuance; the Certificate Revocation List, or CRL, which lists revoked certificates; and the Online Certificate Status Protocol, or OCSP, which provides real-time certificate validity checking.