Questions that a PKI wants to answer:

• Is this public key really the key for this website?
• Was the key used to sign valid at the time it signed?
• Who owns the bits of the public key?
• For what purpose can/should the key be used?

A public key infrastructure (PKI) is a set of roles, policies, hardware, software and procedures needed to create, manage, distribute, use, store and revoke digital certificates and manage public-key encryption.

CA: Certificate Authority

VA: Validation Authority

RA: Registration Authority