Shared SSL certificates, also known as wildcard or server-wide certificates, are used to service multiple third level domains.
Thawte determines a wildcard certificate as "a single certificate, with a wildcard character in the domain name field. This allows the certificate to secure multiple hosts within the same domain. For example, a certificate for ' *.domain.com ', could be used for www.domain.com, www1.domain.com, www2.domain.com, in fact, any host in the domain.com domain. When a client checks the host name in this certificate it uses a shell expansion procedure to see if it matches."
According to VeriSign, a shared SSL certificate "enables Internet Service Providers (ISPs) to provide SSL (Secure Sockets Layer) encryption and business authentication to Web business customers, but without the need to issue unique digital certificates to each hosted customer. The service offers ISPs the convenience and streamlined management of a single specially licensed SSL digital certificate to share among multiple hosted web sites".
Shared SSL certificates work only within one domain level. For example, if you get a domain name for *.domain.com, it will work for www.domain.com and subdomain.domain.com. But it won't work for www.subdomain.domain.com or http://domain.com, and visitors' browsers will show a warning message: "The name on the security certificate does not match the name of the site".
Parallels H-Sphere Shared SSL is based on shared IPs and wildcard SSL certificates and is bound to a particular service DNS zone. Since different servers use different shared IPs, Shared SSL is associated with a certain shared IP tag, which identifies these IPs on each server. When you install a wildcard certificate, it is set up on all web servers. Just make sure that shared IPs on the web servers have the same shared IP tag.
Wildcard certificates can be purchased, for instance, at Comodo Ca.
The cost of a shared SSL certificate usually depends on the number of subdomains that it covers and varies depending on the certificate authority.
Important: when obtaining SSL certificate, make sure it is generated for Apache regardless of whether you inted to install it on windows or unix box.
To install a shared SSL certificate:
That will list all your DNS zones that you can provide secure hosting on:
If you have created a temporary wildcard certificate, you can request a permanent wildcard certificate in the future from a trusted certificate authority. To install the SSL certificate, click the Edit icon next to the domain name and enter the certificate key and certificate file. Then click the Upload button.
Sometimes, you may have to use a Certificate Authority File provided with the Certificate by your Certificate Authority (e.g. Comodo Ca, Geotrust, Equifax, etc.). To use the Certificate Authority File, you have to add a line to the apache config of each virtual host that uses shared SSL. Parallels H-Sphere can do this for you: enter the file in the Certificate Authority File text box and click the Upload button.
Note: If you are using more than one shared IP, each of them must have a unique shared IP tag. You can't create more than one certificate on one shared IP tag.
Besides, you can create 'reseller dedicated' DNS zone domain, secure it with your shared SSL and allow resellers to secure their end user third-level domains (registered on this domain) with your own shared SSL.