Certificate Key Matcher — Verify SSL Cert & Private Key

Certificate Key Matcher

Verify that your SSL certificate matches its private key or CSR by comparing modulus hashes — an essential step before installing SSL on your server.

100% Free Modulus Hash Matching Cert + Key + CSR
Select what you want to match
Certificate + Private KeyMost common — verify key matches cert
Certificate + CSRVerify cert was issued for your CSR
CSR + Private KeyVerify CSR was made from your key
Modulus MatchingCryptographically accurate check
3-Way MatchCert, key, or CSR combos
Nothing StoredKeys never logged
Instant ResultMatch check in milliseconds

About Certificate Key Matcher

The Certificate Key Matcher is a free online security tool that verifies whether an SSL certificate and a private key are a matching pair. Before deploying SSL on your server, it is critical to confirm that your certificate and private key correspond to each other — a mismatch will prevent HTTPS from working and cause server errors.

This tool compares the modulus of the certificate and the private key. If they match, you have the correct key for that certificate. If they do not match, you have either the wrong private key or a wrong certificate file.

How to Check Certificate and Key Match

  • Paste your PEM certificate (-----BEGIN CERTIFICATE-----) in the first field
  • Paste your PEM private key (-----BEGIN PRIVATE KEY----- or RSA PRIVATE KEY) in the second field
  • Click Check Match
  • The tool confirms "Match" or "No Match" with the modulus values for comparison

When to Use This Tool

  • After generating a new CSR and receiving your SSL certificate
  • After renewing a certificate to verify the keys still match
  • When migrating SSL between servers to verify file integrity
  • Troubleshooting "SSL handshake failed" errors

Your private key data is processed only in your browser session and is never stored or transmitted. Free, secure, no login required.

Frequently Asked Questions

Why does certificate/key matching matter?
When installing SSL on a server, you must provide the certificate and its corresponding private key. If they don't match, the server will refuse to start or throw an SSL handshake error. This tool lets you verify they match before attempting installation.
How does modulus matching work?
RSA certificates, private keys, and CSRs each contain a modulus — the product of two prime numbers used in RSA cryptography. If the modulus of a certificate equals the modulus of its private key, they are a matching pair. We compare MD5 hashes of the modulus for a quick check.
Is it safe to paste my private key here?
The key is sent over HTTPS and never stored or logged. That said, for maximum security, you can use OpenSSL locally: openssl rsa -noout -modulus -in key.pem | md5sum and compare with openssl x509 -noout -modulus -in cert.pem | md5sum.
What if the certificate and key don't match?
You have the wrong key for your certificate. Common causes: you generated a new CSR+key after already submitting the original CSR to the CA, or you have multiple key files. Check which key file was used when you originally generated the CSR, or reissue the certificate with a new CSR+key pair.

100+ Free SEO Tools — No Signup Needed

Keyword research, backlink checker, plagiarism detector, meta tags & more. All free, all instant.

Explore All Tools