Which of the following processes of PKI (Public Key Infrastructure) ensures that a trust relationship exists and that a certificate is still valid for specific operations?

Certificate issuance is the process by which a CA signs and distributes a certificate to a subject, which occurs before the trust-checking process.

Certificate validation involves verifying the digital signature on the certificate against a trusted Certificate Authority (CA), checking that the certificate is within its validity period, and confirming it has not been revoked via CRL or OCSP. This end-to-end trust verification process is what ensures a certificate can be legitimately used for operations such as authentication, signing, or encryption.

Certificate cryptography is not a defined PKI process - it describes the underlying mathematical mechanisms, not a procedural PKI function.

Certificate revocation is the process of invalidating a certificate before its expiration date, and is one input into the validation process rather than the validation process itself.