Secure Custom Fields
The Secure Custom Field setting for a custom field applies encryption to the field where personal identification information is required for the input. This setting applies to information that is sensitive, and is only required for special business purposes, such as reporting.
To enable the field, on the Custom Field page, click the
                Secure Custom Field check box. To grant view permission for
            the unencrypted input, select the View Sensitive Data check box
            in the Permissions section for a user. For more information about
            user permissions in a client organization, see Client User Permissions.
    Note: Use of BYOK encryption
                does not change the functionality or permission requirements of secure custom
                fields.