Technical Implementation of Certificates in HTTPS

When a browser connects to an HTTPS server, the certificate enables the secure connection through the TLS handshake process. The server presents its certificate during the handshake, allowing the browser to verify the server's identity and extract the public key for secure communication. This verification includes checking the certificate signature, validity period, domain matching, and revocation status. Any failure in these checks results in browser warnings or connection termination.

Certificate chain verification ensures trust from the server certificate to a known root. Browsers maintain stores of trusted root certificates, updated through operating system or browser updates. The server must provide intermediate certificates to complete the chain, as browsers typically don't cache these. Proper chain configuration prevents validation failures that would otherwise block user access despite valid certificates.

Session establishment uses the certificate's public key to securely exchange or derive symmetric encryption keys. In RSA key exchange, the client encrypts a pre-master secret with the server's public key. In Diffie-Hellman exchanges, the certificate authenticates the server's key exchange parameters. Modern forward secrecy schemes generate ephemeral keys for each session, with certificates providing authentication rather than encryption keys.

Revocation checking ensures certificates remain valid throughout their lifetime. Online Certificate Status Protocol (OCSP) allows browsers to check certificate status with the CA in real-time. OCSP stapling improves performance by having servers fetch and cache OCSP responses, including them in the TLS handshake. Certificate Revocation Lists (CRLs) provide an alternative mechanism, though their size and update frequency make them less practical for modern use.