How does the comparison work?

It extracts the RSA modulus (the core value of the public key) from both the certificate (or CSR) and the private key, then checks whether the two values match.

Are both PKCS#1 and PKCS#8 private keys supported?

Yes. It recognizes both -----BEGIN RSA PRIVATE KEY----- (PKCS#1) and -----BEGIN PRIVATE KEY----- (PKCS#8) formats.

🤝 SSL Certificate & Private Key Matcher

Compare the RSA modulus of a certificate and a private key (PKCS#1/PKCS#8) to check whether they're a matching pair.

⚠️ Currently only RSA keys are supported (EC keys not supported)

Certificate PEM (or CSR PEM)

Private Key PEM

How to use

Enter the certificate (or CSR) PEM.
Enter the private key PEM.
Click "Compare" to check whether they match.

🎯 Use Cases

Confirm the certificate and private key are a matching pair before deploying to a server
Find the correct private key among several certificate files
Verify a key file swap after certificate renewal

Example

Input

Certificate PEM:
-----BEGIN CERTIFICATE-----
MIIDDTCCAfWgAwIBAgIUe/13kqiwei2z7puPaEtsEewQs/Mw…
-----END CERTIFICATE-----

Private Key PEM:
-----BEGIN PRIVATE KEY-----
MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIB…
-----END PRIVATE KEY-----

Output

✅ The certificate and private key match (same key pair)

Given a self-signed certificate for example.com and its own private key, the RSA modulus extracted from each side is identical, so they are reported as the same key pair. Mismatched keys would instead show "❌ different key pairs".

FAQ

How does the comparison work?: It extracts the RSA modulus (the core value of the public key) from both the certificate (or CSR) and the private key, then checks whether the two values match.
Are both PKCS#1 and PKCS#8 private keys supported?: Yes. It recognizes both -----BEGIN RSA PRIVATE KEY-----(PKCS#1) and -----BEGIN PRIVATE KEY-----(PKCS#8) formats.
Are EC (elliptic curve) keys supported?: Currently only RSA keys are supported.