As is obvious from the name SSL VPN, the Secure Sockets Layer protocol (SSL) is a key element of SSL VPN technology. As such, a basic understanding of SSL will help us understand the workings of SSL VPNs.
Web pages are delivered using the Hypertext Transfer Protocol (HTTP) .
HTTP in itself does not offer encryption or any other substantial protection of data transmitted between users and web servers. With the advent of the World Wide Web in the early 1990s and the goal of extending Web usage to actual business activity involving the transmission of confidential information over the Internet came the need to eliminate eavesdropping by unauthorized parties on web communications between computers over the Internet.