If you are putting your SCADA facing the Internet, you may further enhance your SCADA security by applying HTTPS secure connection. HTTPS is a more secure way for a browser and a web server to communicate. This is done by using Secure Sockets Layer (SSL) which is the standard security technology for establishing an encrypted link between a web server and a browser.
With this link, you can be sure that the data being sent between web browser and server stays private without the ability of interception by a third party. This is the similar high security approach like online banking or credit card transaction. An SSL certificate is needed by the server to identify itself and send a public key for the browser to use to establish the encrypted link.