Compare an MD5 hash of the modulus using these commands:
Certificate: openssl x509 -noout -modulus -in server.crt | openssl md5
Private Key: openssl rsa -noout -modulus -in server.key | openssl md5
CSR: openssl req -noout -modulus -in server.csr | openssl md5
If the hashes match, then those two files go together.
reference link:
http://stackoverflow.com/questions/274560/how-do-you-test-a-public-private-keypair
