The correct answer is If the root certificate is installed because trust errors in SSL/TLS deployments most commonly occur when the certificate chain cannot be validated back to a trusted root certificate authority. In the Security+ SY0-701 cryptography and PKI objectives, trust is established through a chain of trust, beginning with a trusted root CA, followed by any intermediate CAs, and ending with the server’s certificate.
In this scenario, the administrator has already confirmed that the certificate was issued by a legitimate CA and that the private key is valid. This eliminates common issues related to key mismatch or improper issuance. The next logical step is to verify that the system (or the client systems connecting to it) trusts the CA that issued the certificate. If the root certificate—or required intermediate certificates—are missing from the trust store, clients will flag the certificate as untrusted even though it is otherwise valid.
Option A, checking wildcard configuration, is not relevant unless the certificate is being used for multiple subdomains, which is not indicated. Option B, validating the certificate signing request, would be unnecessary because the CA successfully issued the certificate. Option D, verifying the public key, is incorrect because the public key is embedded in the certificate and would already be validated as part of successful issuance.
The SY0-701 study guide highlights that certificate trust failures are frequently caused by incomplete certificate chains, missing root or intermediate certificates, or misconfigured trust stores. Ensuring that the correct root CA certificate is installed allows systems to verify the certificate’s authenticity and establish secure communications.
In summary, when an SSL certificate is valid but not trusted, the most likely cause is a missing trusted root certificate, making option C the correct answer.
