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 CA process of signing and distributing a certificate to a subject - it creates the certificate but does not verify its ongoing trustworthiness.

Certificate validation is the formal PKI process of checking that a certificate chains up to a trusted root CA, has not expired, has not been revoked (via CRL or OCSP), and is appropriate for the intended purpose (e.g., code signing vs. TLS). It is the mechanism that establishes whether a trust relationship is present and whether the certificate can be relied upon for a specific operation.

Certificate cryptography is not a defined PKI process; it is a generic term describing the mathematical operations involved, not a lifecycle management step.

Certificate revocation is the act of invalidating a certificate before its expiration - it is one input into validation, but it is not itself the process of confirming trust and validity.