How do I match a certificate file to a key file?
Compare the modulus of the files.
Check the public key like this:
openssl x509 -in /path/to/cert.crt -noout -text
And check the private keys like this:
openssl rsa -in /path/to/cert.key -noout -text
Compare the "modulus" data (a big block of numbers) between the certificate and the potentially matching keys. If they match, then the key and certificate are a pair.