Generate Private Key for Existing SSL Certificate

Question

I have been provided with a Comodo SSL certificate to deploy with Apache/ModSSL on Ubuntu 14.04. All I got was an email with links like this. I was not provided with a private key. It appears the enrolment process can be done entirely from Comodo's website.

Comodo support tells me I have to generate the private key and CSR separately. I get "mismatch" errors when I use a newly generated private key as SSLCertificateKeyFile:

SSL Library Error: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch

How can I deploy the certificate?

Solution

This is not how certificates work. You can't generate a private key for an existing SSL certificate. First you generate the key pair (private + public), then you generate a CSR (containing your public key) that you forward to the CA (Comodo in this case) which will provide you with the certificate to install on your server.

Perhaps the private key is still somewhere in your system -- it should be a .key file. Which command did you use to make the CSR? Note that if you don't have the private key anymore then this certificate is useless and you'll need to request a new one.

Edit: possible duplicate of Apache - Generate private key from an existing .crt file