HTTPS (HTTP over SSL or HTTP Secure) is the use of Secure Socket Layer (SSL) or Transport Layer Security (TLS) as a sublayer under regular HTTP application layering. HTTPS encrypts and decrypts user page requests as well as the pages that are returned by the Web server. The use of HTTPS protects against eavesdropping and

man-in-the-middle attacks. HTTPS was developed by Netscape.
HTTPS and SSL support the use of X.509 digital certificates from the server so that, if necessary, a user can authenticate the sender. Unless a different port is specified, HTTPS uses port 443 instead of HTTP port 80 in its interactions with the lower layer, TCP/IP.

Suppose you visit a Web site to view their online catalog. When you’re ready to order, you will be given a Web page order form with a Uniform Resource Locator (URL) that starts with https://. When you click “Send,” to send the page back to the catalog retailer, your browser’s HTTPS layer will encrypt it. The acknowledgement you receive from the server will also travel in encrypted form, arrive with an https:// URL, and be decrypted for you by your browser’s HTTPS sublayer.