Verify whether a Certificate (.crt) or CSR (.csr) matches your Private Key (.key) before server deployment. Avoid web server downtime and SSL startup errors with instant, 100% client-side cryptographic modulus checking.
Your Private Key stays 100% inside your browser memory. No private keys or certs are ever transmitted or stored.
Match Certificate vs Private Key, CSR vs Private Key, or verify Certificate vs CSR with automatic format detection.
Calculates exact MD5 & SHA-256 modulus hashes identical to 'openssl x509 -noout -modulus | openssl md5'.
Paste your Certificate / CSR and Private Key below to check their cryptographic compatibility.
| Modulus MD5 Hash |
Item 1:
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Item 2:
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✔ Matches |
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| Modulus SHA-256 Hash |
Item 1:
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Item 2:
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✔ Matches |
Prevent web server startup failures and understand the underlying mathematics of public-key cryptography.
When Apache, Nginx, or IIS starts, it verifies that the SSL certificate matches the private key directive. If there is a mismatch, the server will abort restart with fatal errors, causing sudden website downtime.
In RSA asymmetric cryptography, both the public certificate and private key contain the exact same mathematical Modulus (N). By hashing this modulus, we can prove a 100% match without exposing private key secrets.
If your private key does not match your certificate, you cannot decrypt TLS traffic. Simply generate a fresh CSR & Key using our CSR Generator, then submit a free Reissue in your RenewalSSL control panel.
Everything you need to know about key matching, OpenSSL parity, and troubleshooting.
RenewalSSL provides free, unlimited reissues and expert 24/7 technical support for Sectigo, DigiCert, and GeoTrust SSL certificates.
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