Setting up SSL for subdomains, IP address how do

If you use one certificate, it will have to be valid for any hostname you want to use with it. In this case, kickassapp.com, www.kickassapp.com, and hi.kickassapp.com. Some certificate authorities will do this in one certificate, using the Certificate Subject Alternative Name field.

You might be able to optimize this a bit if you use just one hostname for SSL traffic. Most folks aren't going to do https://hi.kickassapp.com/; rather, they're going to go to hi.kickassapp.com and then you're going to redirect to https. What I would do is get a certificate for kickassapp.com (and www.kickassapp.com, if they'll throw it in for free), and redirect hi.kickassapp.com to https://kickassapp.com/hi/. This will throw a cert error if someone goes to https://hi.kickassapp.com/, but it is usually an obvious and self-explanatory error.

Multiple certificates are also a possibility. It is no longer the case that you must have a separate IP address for each SSL certificate (see here for why). BUT! – and this is a big but, I cannot lie -- it is not supported by all browsers/operating systems yet. Notably, Windows XP and Android 2.x lack support for it.

To summarize: SSL is a mess, certificates are a mess, IPv4 is a mess, Windows XP is a mess, and you'll probably want to present one certificate per IP/port, and that certificate better recognize the hostname the browser is connecting to. Or adopt a "IPv6, SNI, or GTFO" policy and tell XP users without IPv6 to get with the program :-)