To review a current list of Salesforce supported certificates, you can append /cacerts.jsp to any instance URL.

Syntax:

https://INSTANCE.salesforce.com/cacerts.jsp

Example:

https://cs32.salesforce.com/cacerts.jsp

Note:

Salesforce trusts only root certificate authority (CA) certificates, with few historical exceptions. Salesforce’s certificate trust policy is to require server and client certificate chains to include all intermediate certificates that exist between the server or client certificate and the chain’s root certificate. Salesforce will not honor requests to add intermediate certificates to its trust list. Salesforce trusts many generally trusted root certificates, but not all.