Target audience that doesn't understand openssl

You're often too literal, especially given your audience is going to be largely people that find it too complex to do it manually themselves. People don't think of "common names", they think "url" or "hostname".
Again on the literal front, you've copied the OpenSSL descriptions of OU and stuff and expect the user to know what it is. Fill in sample data or placeholder so that it helps the user figure out what they want, should they want to customize it. Consider removing fields if no one cares.
Do you even need the second screen? You could just put "domain name" and "secret key passphrase" on the front page and go straight to the download after that

dimastopel / certdepot