How can I extract a key from an SSL certificate?

Question

I have an SSL certificate I purchased in a .pem, .crt, .der format. I was wondering how I get the key file from the certificate. Is there any way of doing this?

Answer 1

You can extract the public key. This has limited usefulness. Perhaps you are going to use the same key with another tool like SSH or PGP that doesn't use certificates.

With OpenSSL:

openssl x509 -pubkey -noout < cert.pem > pubkey.pem

You can't derive the private key from a certificate. That would make the whole thing quite pointless, wouldn't it?