How to compare X509 certificate object with another .pem extension certificate

Question

I have two .pem files(certificate and RSA private key) of a certificate. And I am fetching a X509 openSSL certificate object from server. How should I compare this two certificate to make sure they are same or different?

Answer 1

One way to do this is to extract each PEM to text and comapre the texts:

$ openssl x509 -in a.crt -text -noout > a.crt.txt
$ openssl x509 -in b.crt -text -noout > b.crt.txt
$ diff a.crt.txt a.crt.txt

or, as a single command

$ diff <(openssl x509 -in a.crt -text -noout) <(openssl x509 -in b.crt -text -noout)

I found myself in the curious position of having two different PEM representations of the same certificate. Comparing PEMs failed but the above confirmed them to be the same.