Trusted CA
Click Security > Certificates > Trusted CA to open the following screen. This screen displays a summary list of certificates of the certification authorities that you have set the Zyxel Device to accept as trusted. The Zyxel Device accepts any valid certificate signed by a certification authority on this list as being trustworthy, which means you do not need to import any certificate that is signed by one of these certification authorities.
*A maximum of ten certificates can be added.
Security > Certificates > Trusted CA
The following table describes the labels in this screen.
Security > Certificates > Trusted CA 
Import Certificate
Click this to open a screen where you can save the certificate of a certification authority that you trust to the Zyxel Device.
This is the index number of the entry.
This field displays the name used to identify this certificate.
This field displays information that identifies the owner of the certificate, such as Common Name (CN), OU (Organizational Unit or department), Organization (O), State (ST) and Country (C). It is recommended that each certificate have a unique subject information.
This field displays general information about the certificate. ca means that a Certification Authority signed the certificate.
Click the View icon to open a screen with an in-depth list of information about the certificate (or certification request).
Click the Remove icon to delete the certificate (or certification request). You cannot delete a certificate that one or more features is configured to use.