Cash value is carried on the card itself, so the need for central processing is eliminated. Transactions of a few dollars or even cents become viable, and the need to fumble around for loose change is eliminated. Cards can be programmed with a security, ensuring that only the owner can use it, another advantage over cash. They can be used and have value added by using a special card reader, which can even be attached to a PC for purchases over the Internet. The largest smart card system is from Mondex , run by MasterCard.
None are yet official, but each is supported by various web browsers and sites.
SSL stands for secure socket layer, and is widely implemented. SSL is in use when the address of the site you are visiting begins with https. SET is a fourth protocol, especially supported by the credit card companies. It is currently under consideration to be the universal standard, and it will likely become dominant in the future. All are secure means of shopping online.