Most e-commerce vendors use this method to secure the information being transmitted. The protocol begins with a handshake phase that negotiates an encryption algorithm and keys and authenticates the server to the client. Once the handshake is complete and transmission of application data begins, all data is encrypted using the session keys negotiated during the handshake. In plain English, this means that when your browser connects to a secure web site, the web server and your browser establish a formula that will be used to encrypt the transmissions that follow. Encryption means that all information relating to you and your account is scrambled and locked with a mathematical key during the electronic transfer.
Most browsers have an icon such as a key or a lock to represent an encrypted mode or session.
A broken key , open lock , or no lock indicates that the session or mode is not encrypted. For example, if you are about to send your credit-card number to an unsecure site, Internet Explorer can warn you that the site is not secure. If the site claims to be secure but its security credentials are suspect, Internet Explorer can warn you that the site might have been tampered with or might be misrepresenting itself. It ensures that no other Web site can assume the identity of the original secure site. Web site certificates are also dated when they are issued.