Certificate Key Matcher | Check SSL Key Pair

Certificate key matcher that checks whether an SSL certificate or CSR matches its private key. RSA, EC and Ed25519 PEM keys, compared in your browser. Free. Designed specifically for developers and professionals, this free online validator runs entirely in your browser to process tasks quickly and securely. Enjoy unlimited usage with no data tracking and no registration required.

Also known as: certificate key matcher · check if certificate matches private key · ssl certificate key matcher · verify certificate and private key match · csr private key match · ssl key matcher online · openssl check private key matches certificate · key values mismatch · rsa modulus match checker · private key mismatch checker

ssl and security tools

encryption tools

validators

Certificate and Key Input

Certificate, chain or CSR (PEM)

Private key (PEM)The key is checked in this tab. It is never uploaded, and never saved, even with Pro auto-save.

Match Result

Paste a certificate and its private key, then click Check Match. The result shows here.

About Certificate Key Matcher

A certificate key matcher tells you whether a private key belongs to an SSL/TLS certificate or CSR before you install the pair on nginx, Apache, HAProxy or a load balancer. It rebuilds the public key from the private key, compares it with the public key inside the certificate, and shows both SHA-256 fingerprints with the OpenSSL commands that print the same values. Nothing is uploaded.

Key Features

Compares RSA, RSA-PSS, EC (P-256, P-384, P-521) and Ed25519 keys against certificates, CSRs and public keys
Reads PKCS #8 (BEGIN PRIVATE KEY), PKCS #1 (BEGIN RSA PRIVATE KEY) and SEC 1 (BEGIN EC PRIVATE KEY) keys, as PEM text or DER uploads
Checks every certificate in a fullchain.pem bundle and tells you when the matching one is not first
Shows the SPKI SHA-256 fingerprint of both sides plus the two OpenSSL commands that reproduce them
Lists the certificate's SANs, expiration date and days remaining while it checks the key
Runs in your browser: the private key is never uploaded and never saved to local storage

Use Cases

Fixing an nginx key values mismatch error after a certificate renewal
Finding which of several .key files on a server belongs to the new certificate from your CA
Confirming a CSR was generated from the key you kept before you order an OV or EV certificate
Catching a fullchain.pem where the intermediate certificate ended up before the server certificate
Checking a pair before you import it into AWS Certificate Manager, Cloudflare or a Kubernetes TLS secret

Supported Formats

PEM

DER

X.509 certificate

PKCS #10 CSR

PKCS #8

PKCS #1

SEC 1

Related Keywords

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check if certificate matches private key

ssl certificate key matcher

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csr private key match

ssl key matcher online

openssl check private key matches certificate

key values mismatch

rsa modulus match checker

private key mismatch checker

What does "key values mismatch" mean?

OpenSSL 3 prints error:05800074:x509 certificate routines::key values mismatch when the configured private key does not belong to the certificate, and servers built on OpenSSL, such as nginx, log the same error. Python reports it as KEY_VALUES_MISMATCH and Node.js as ERR_OSSL_X509_KEY_VALUES_MISMATCH. The usual causes are a key left over from an older CSR, or a bundle with the intermediate certificate placed before the server certificate. This tool tells you which of the two you have.

Privacy & Security

All processing happens locally in your browser. Your data never leaves your computer, ensuring complete privacy and security.

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Frequently asked questions

What is Certificate Key Matcher used for?

Certificate key matcher that checks whether an SSL certificate or CSR matches its private key. RSA, EC and Ed25519 PEM keys, compared in your browser. Free.

Is Certificate Key Matcher free to use?

Yes. Certificate Key Matcher is completely free with no usage limits, and there is no paid tier required to use it.

Do I need an account to use Certificate Key Matcher?

No. Certificate Key Matcher works immediately in your browser with no signup, login, or email address required.

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