where is the encryption key for membership/roles stored?

I have my website on a shared server.  I plan to use the membership/roles classes offered by asp.net but until now I've been using my own code to do the same thing.  My question is this.  Currently, I'm using a key stored in my web.config to do the encryption of my log-in cookies.  When I switch to the role-classes, will the encryption key be somewhere else on the server?  Could another user of the same server be using the same key?

Thanks.