A wildcard SSL certificate enables you to secure a website’s domain and an unlimited number of its subdomains. For example, a single wildcard certificate could secure both www.yourcompany.com, anddeals.yourcompany.com.
Note: Extended Validation (EV) certificates do not support the concept of a wildcard, but they do work with Subject Alternative Names (SANs), which enable the use of extra fully-qualified domain names and subdomain names.
Wildcard certificates enable the securing all of the subdomains at the level specified when you submit your certificate request. Add an asterisk (*) in the subdomain part of the common name (CN) where you want to use the wildcard.
If you configure *.yourcompany.com, you can secure www.yourcompany.com, deals.yourcompany.com, info.yourcompany.com, etc.
If you configure *.www.yourcompany.com, you can secure mail.www.yourcompany.com, deals.www.yourcompany.com, info.www.yourcompany.com, etc.
Note: A wildcard certificate secures only the level of subdomain you specify. So, if a certificate is configured for*.www.yourcompany.com, it will not secure www.yourcompany.com.
Wildcard certificates secure websites the same way as a regular SSL certificate, and requests are processed using the same validation methods. However, some web servers may require a unique IP address for each subdomain on the wildcard certificate.
EV certificates do not support the concept of a wildcard, but they do work with SANs, which enable the use of extra fully-qualified domain names and subdomain names.