Free SSL Tools
Inspect live HTTPS servers, generate 2048/4096-bit CSRs, decode X.509 PEM certificates, and verify Private Key modulus matching.
Live HTTPS / SSL Server Inspector
Enter any hostname to inspect its active SSL certificate, issuer chain, and expiration countdown.
Understanding SSL/TLS Diagnostics, CSR Generation & X.509 Certificate Verification
Properly configuring Transport Layer Security (TLS 1.2 and TLS 1.3) requires accurate cryptographic key pairs, complete intermediate Certificate Authority (CA) chains, and timely certificate renewals. Below is a comprehensive engineering breakdown of how each diagnostic utility in our suite works.
1. How the Live Port 443 SSL Checker Works
Our Live SSL Server Checker initiates a real-time TLS handshake with your target hostname on port 443 using Server Name Indication (SNI). It extracts the X.509 peer certificate and intermediate chain, measures handshake latency in milliseconds, verifies the Common Name (CN) and Subject Alternative Names (SANs), and calculates the exact number of days remaining before expiration.
2. What is a Certificate Signing Request (CSR) & RSA Private Key?
A Certificate Signing Request (CSR) is an ASN.1 PKCS#10 block encoded in PEM format containing your domain Distinguished Name (DN) fields and your Public Key. When you generate a 2048-bit or 4096-bit RSA key pair using our generator, the Private Key must be stored securely on your web server, while the CSR is submitted to the Certificate Authority (CA).
3. Why Decode X.509 PEM Certificates & CSRsBefore Deployment?
Before deploying a newly issued ".crt" or ".pem" file to production Apache or Nginx servers, administrators use the X.509 Decoder to verify that all required Subject Alternative Names (including both root apex and *.wildcard entries) are present, and to inspect the SHA-256 thumbprint and issuer chain.
4. Preventing nginx/Apache "Key Values Mismatch" Errors
One of the most frequent web server startup failures during SSL renewal is "SSL_CTX_check_private_key: key values mismatch". Our Key Matcher computes and compares the SHA-256 digest of the public key modulus inside both your Certificate and Private Key so you can confirm they belong to the exact same key pair.