protected function generatePrivateKey($path, $passphrase)
    {
        if ($passphrase) {
            $processArgs = sprintf('genrsa -out %s/private.pem -aes256 -passout pass:%s 4096', $path, $passphrase);
        } else {
            $processArgs = sprintf('genrsa -out %s/private.pem 4096', $path);
        }

        $this->generateKey($processArgs);
    }