To back up your Public Certificates and My Certificates lists:
On the Settings page - SSL Manager tab, select Backup in the SSL Manager Tasks panel. The Save window appears.
On the Save window, navigate to the folder where you want to save the backup.
In the File Name field, enter a name for the certificate backup file.
In the Files of Type field, ensure that the Mirth Key Store (*.mks) format is selected, then select Save. The backup should be saved as a special .mks file.