I've a website for a few users, very "confidential", only for certain userid from certain IP address.

I need use also SSL for encrypt the conversations.
Please what is your comment or recommendation for this.

Now the operative is:

1.- end user enter in normal-web.com
2.- host detect the enduser IP and if ok
3.- redirect to firewall IP in DMZ
4.- firewall redirect to the intranet IP AND PORT 6031
5.- show page with login (UserId and PassWord) and use the app

thus: users enter in an normal website using port 80, this redirect to public IP in firewall, and firewall redirect to the machine IP but using Port X.

maybe the Port will be changed, or even we can needed two or three ports for different content.

In this environment...
How can implement SSL ?
I think SSL need to be applied to domain, but I've not domain except the first one but it is only used to redirect.
Can I use the firewalled public IP?
Can I use this independent of the port, or are needed an different certificate for each port?

Thanks very much in advance.