Subject Alternative Names (SAN) is a feature available on select SSL Certificates which allows for multiple domain names to be protected under the one certificate.
Purpose of a SAN certificate
The purpose of a SAN Certificate ( also named Multi Domain Certificate )is the same as an SSL Certificate: to authenticate the identity of the website and allow a secure connection to be established. However, SAN SSL Certificates are able to secure more then one domain name with a single certificate.
How does it work?
A list of host names to be protected under a single SSL are specified in the management tool. Thereby protecting those listed domains with the one certificate.
Why use it?
SAN SSL Certificates are powerful tools for creating a cost effective solution for customers with multiple domains that require security. There is no requirement for the domains to be related.
Save money by avoiding purchasing multiple SSL certificates, and save time by managing all the domains under one certificate in the one location.
Example:
A website is set up with the following domains:
http:// www.domain.com
http:// domain.com
Both of these websites have different DNS (Domain Name System) name spaces and if the administrator wanted to create a secure site (https://) for both of them, then two SSL certificate would need to be purchased (one for each domain) since an SSL certificate does not recognise that the domains are related due to the different DNS name spaces. The downside to purchasing two separate SSL certificates is the cost and increase in management.
A better alternative is the SAN SSL Certificate, which will allow the administrator to secure both websites (even though they are using different DNS namespaces) with the one certificate and manage the certificate of both sites in the one location.