SSL certificate for Website behind a closed sonicwall? -

i'm trying understand if need ssl cert website have on hosted box accessible allowed list setup on our sonicwall.

so have client , ip ip address access through our sonicwall on port 80 web server. other ip's blocked @ sonicwall. ip setup within iis in "ip address , domain restrictions". other ip's , set deny. need ssl cert web site?

thanks

restriction ip address helps restrict can access site not secure data transfer itself. means passive data sniffing still possible.