What does a digital certificate system primarily use to validate a user's identity?

A digital certificate system primarily uses third-party Certificate Authorities (CAs) to validate a user's identity. The role of a CA is to issue digital certificates that authenticate the identity of individuals or organizations. When a user applies for a digital certificate, the CA verifies their identity through various means, depending on the level of assurance required. Once verified, the CA issues a certificate that includes the user's public key and other identifying information, ensuring that the public key belongs to the holder of the certificate.

This process enables secure communications over the internet and helps prevent impersonation and man-in-the-middle attacks. By relying on a trusted third-party CA, users and systems can have confidence in the authenticity of certificates they encounter.

In contrast, digital signatures are used for ensuring the integrity and authenticity of a message or document, but they do not themselves validate a user's identity independently. Tokens can also be part of an identity management system, often used for authentication, but they do not replace the role of a CA in issuing digital certificates. Personal correspondence does not provide a reliable or standardized method of verifying identity in a digital context.