PGP uses what sort of system to verify the identity of the certificate holder?

PGP, or Pretty Good Privacy, uses a Web of Trust system to verify the identity of certificate holders. This approach allows individuals to own keys that validate the authenticity of their digital signatures based on their trust in other users' keys rather than relying on a central authority. Each user can sign the public keys of other users they know and trust, creating a decentralized and distributed network of trust relationships.

In contrast, other systems like Public Key Infrastructure (PKI) rely on centralized authorities to issue and manage digital certificates, which differs fundamentally from the trust model used in PGP. The Centralized Trust Model and Direct Trust Model also do not align with the decentralized nature of PGP's Web of Trust, which empowers users to determine whom they trust based on personal interactions and relationships rather than a top-down approach. This decentralized trust approach fosters a more democratic and flexible model for validating identities in a variety of scenarios.