DigiCert is one of the market leader in PKI SSL Certificates and other digital security products. We have featured Digicert elsewhere on this website.
What is import to say is it is not recommended to go to digicert.com to buy an SSL Certifcate, go to Digicert.com to inquire on being an Enterprise Client for the PKI infrastructure, Sub-CA or other enterprise solutions.
Digicert SSL brands includes Symantec, RapidSSL, GeoTrust, VeriSign, Norton
Here is a feature and comparison of Digicert SSL prices versus AskSSL.com prices