I believe RDP uses RC4 with a maximum of 128 bit encryption
. Thats pretty secure if you ask me. It will take quite a bit of effort to break that. Incase you must use RDP
because you have Windows
servers in your environment I'd recommend you use a tool called SecureRDP
which can limit the IP addresses that can access your Windows servers.
This ofcourse is a third party tool and its up to you to whether you want to trust it or not.
p.s..... Lastly this is a Linux forum and RDP is a Windows based technology so you'd get much more help on a Windows forum somewhere on the Internet.