How Credit Cards Work

Smart Cards

­The "smart" credit card is an innovative application that involves all aspects of cryptography (secret codes), not just the authentication we described in the last section. A smart card has a microprocessor built into the card itself. Cryptography is essential to the functioning of these cards in several ways:

  • The user must corroborate his identity to the card each time a transaction is made, in much the same way that a PIN is used with an ATM.
  • The card and the card reader execute a sequence of encrypted sign/countersign-like exchanges to verify that each is dealing with a legitimate counterpart.
  • Once this has been established, the transaction itself is carried out in encrypted form to prevent anyone, including the cardholder or the merchant whose card reader is involved, from "eavesdropping" on the exchange and later impersonating either party to defraud the system.

­This elaborate protocol is conducted in such a way that it is invisible to the user, except for the necessity of entering a PIN to begin the transaction.


Smart cards first saw general use in France in 1984. They are now hot commodities that are expected to replace the simple plastic cards most of us use now. Visa and MasterCard are leading the way in the United States with their smart card technologies.

The chips in these cards are capable of many kinds of transactions. For example, you could make purchases from your credit account, debit account or from a stored account value that's reloadable. The enhanced memory and processing capacity of the smart card is many times that of traditional magnetic-stripe cards and can accommodate several different applications on a single card. It can also hold identification information, keep track of your participation in an affinity (loyalty) program or provide access to your office. This means no more shuffling through cards in your wallet to find the right one -- the smart card will be the only one you need!

Experts say that internationally accepted smart cards will be increasingly available over the next several years. Many parts of the world already use them, but their reach is limited. The smart card will eventually be available to anyone who wants one, but for now, it's available mostly to those participating in special programs.

For more information on one particular type of smart card, check out How Blink Technology Works.