If you do not have a customer certificate key pair, use the options on the Configure > SSL > Custom Certificate Key > Create Custom Certificate Key tab.
Steps
Enter the Key length.
Valid vales are 2048 or 4096.
Enter a Passphrase and then Confirm Passphrase.
Enter a phrase that is 4-40 characters in length. The passphrase and confirm passphrase entries must match.
Click Generate and Deploy Custom Certificate Key.
Be sure to click this option only once. The process may take several seconds.
Content Gateway must be restarted in order to use this new customer key.