Installing Intermediate Certificates and Chain Configuration

Intermediate certificates form crucial links in the certificate chain of trust, connecting server certificates to trusted root certificates in browsers. Failure to properly install intermediate certificates results in browser warnings about untrusted certificates, even when the server certificate itself is valid. This common misconfiguration frustrates users and damages credibility, yet remains easily preventable through proper chain configuration.

Certificate authorities provide intermediate certificates along with server certificates, typically as separate files or bundled packages. The installation process requires concatenating certificates in the correct order: server certificate first, followed by intermediate certificates in order from the issuing intermediate to the root. This ordering allows browsers to build the complete chain from server to trusted root. Some platforms handle this automatically, while others require manual chain construction.

Testing certificate chains prevents deployment of incomplete configurations. Tools like OpenSSL's s_client command verify complete chains from server certificates to trusted roots. Online SSL testing services like SSL Labs' SSL Test provide comprehensive analysis of certificate chains, protocols, and cipher configurations. These tools identify missing intermediate certificates, incorrect ordering, and other chain-related issues before they impact users.

Modern approaches to chain configuration include OCSP stapling and CT logs. OCSP stapling attaches certificate revocation status to the handshake, eliminating browser OCSP lookup delays. Certificate Transparency logs provide public records of certificate issuance, helping detect misissued certificates. Implementing these features enhances security and performance while demonstrating commitment to best practices.