What Is Port 443? HTTPS, TLS & Web Security Explained

Why Does HTTPS Use Port 443?

Port numbers are assigned by the Internet Assigned Numbers Authority (IANA) to distinguish different network services running on the same server. Port 443 was officially assigned to HTTPS by IANA in RFC 2818.

When you visit https://example.com, your browser automatically connects to port 443 on the web server. If port 443 is blocked by a firewall or the server isn't listening, the connection fails with a 'Connection Refused' or 'ERR_CONNECTION_TIMED_OUT' error.

Port 80 is for unencrypted HTTP. The industry standard is to have your server redirect all port 80 traffic to port 443 using a permanent 301 redirect.

How TLS Encryption Works on Port 443

TLS (Transport Layer Security) is the cryptographic protocol that makes HTTPS secure. When a browser connects to port 443, a TLS handshake occurs before any HTTP data is transmitted:

1. Client Hello: The browser sends supported TLS versions and cipher suites.

2. Server Hello: The server selects the strongest mutual cipher suite and sends its SSL/TLS certificate.

3. Certificate Verification: The browser verifies the certificate is signed by a trusted Certificate Authority (CA) like Let's Encrypt or DigiCert.

4. Key Exchange: Both parties generate a session key using asymmetric cryptography (RSA or ECDH).

5. Encrypted Channel: All subsequent HTTP data is encrypted symmetrically with AES-256 or ChaCha20.

Browser              Web Server (Port 443)
   |--- ClientHello  ------>  |
   |<-- ServerHello + Cert -- |
   |--- Verify Cert + Key --> |
   |<-- Finished (Encrypted)  |
   |=== HTTPS Data (AES) ====>|

How to Check If Port 443 Is Open on Your Server

Use our free Open Port Checker tool to verify port 443 is publicly reachable from the internet — paste your server's IP address or domain name and test port 443.

From the command line, use: curl -v https://yourdomain.com (checks full TLS handshake) or openssl s_client -connect yourdomain.com:443 (shows certificate details and TLS version).

Common reasons port 443 fails: SSL certificate expired or misconfigured, Nginx/Apache not listening on 443, cloud firewall (AWS Security Group) blocking inbound TCP 443, or server IP mismatch in A record.