I have an application that communicates via SSL, however, Port 443 is already in use by an IIS instance on that same server. Can I use another port other than 443 for SSL communication?
SSL is in no way tied to a single port value; in fact, as a protocol, it can be used over any transport medium, as long as that medium provides a bidirectional stream for arbitrary bytes.
In a Web context, you can use any port other than 443, provided that you specify it in the URL:
Note that there are some networks (especially some free WiFi access points) that don't allow traffic over other ports than 443 or 80; which means that using a port other than 443, though perfectly standard and supported, may imply some practical usage restrictions.
You can use (nearly) every port, which is not used, for SSL communication. The question is: Did you mean that someone enters
https://... and your service is not on port 443? Than it is not directly possible. Modern browsers use the prefix
https:// to connect to
serveraddress:443 (if no port is present). Similar to
http:// which connects to
On Apache you can do this on the same port: http://www.digicert.com/ssl-support/apache-multiple-ssl-certificates-using-sni.htm