Since I wasn't familiar with generating keys and certificates, I had some testing to do at the time. Now I feel that a certain pair might have been mixed up.
I have one RSA Private key file:
-----BEGIN RSA PRIVATE KEY-----
...
-----END RSA PRIVATE KEY-----
and the certificate signing request file sent to the other party:
-----BEGIN CERTIFICATE REQUEST-----
...
-----END CERTIFICATE REQUEST-----
Whilst trying to check the match, with information found on the Web, it might be worth noting that the following:
openssl x509 -noout -modulus -in cert.csr | openssl md5
Gives the following error:
unable to load certificate
4980:error:0906D06C:PEM routines:PEM_read_bio:no start line:.\crypto\pem\pem_lib.c:650:Expecting: TRUSTED CERTIFICATE
Although it still gives me and md5 hash. Running a similar command on the private key produces another md5. Since these don't match, can I assume now, that the csr was not generated from the key?
I was able to check the stored values in the csr with the following command:
openssl req -in cert.csr -noout -text
I tried generating a new one with the same values. This did not give me the exact same result - only the first three lines were the same.
Is there a way to check if the csr and pem files really match or there has been a mixup?
Okay, so I figured it out, since I didn't find a suitable answer on the web myself and in case anyone else needs it... Might not be the best way, but at least gave the desired result.
I ran two commands. This one on the private key file:
openssl rsa -noout -modulus -in key.pem
The following on the certificate:
openssl req -noout -modulus -in cert.csr
If the outputs matched, the key and certificate matched.
Found the correct private key and was able to restore the correct one from the repository.