“How Credit Cards Work”As we had earlier on said, the initial credit card system was licensed in USA starting in 1966, and was renamed Visa in 1976. Other major bank cards followed, including MasterCard, formerly Master Charge. In order to offer expanded services, such as meals and lodging, many smaller banks that earlier offered credit cards on a local or regional basis formed relationships with large national or international banks. The first digit in your credit-card number signifies the system: 3 - travel/entertainment cards (such as American Express and Diners Club) 4 – Visa, 5 – MasterCard, 6 - Discover Card. The structure of the card number varies by system. For example, American Express card numbers start with 37; Carte Blanche and Diners Club with 38. American Express - Digits three and four are type and currency, digits five through 11 are the account number, digits 12 through 14 are the card number within the account and digit 15 is a check digit. Visa - Digits two through six are the bank number, digits seven through 12 or seven through 15 are the account number and digit 13 or 16 is a check digit. MasterCard - Digits two and three, two through four, two through five or two through six are the bank number (depending on whether digit two is a 1, 2, 3 or other). The digits after the bank number up through digit 15 are the account number, and digit 16 is a check digit. In addition to the digits, there is also Stripe on a Credit Card; the stripe on the back of a credit card is a magnetic stripe, often called a magstripe. The magstripe is made up of tiny based magnetic particles in a plastic-like film. Each particle is really a tiny bar magnet about 20-millionths of an inch long. The magstripe can be “written” because the tiny bar magnets can be magnetized in either a north or South Pole direction. The magstripe on the back of the card is very similar to a piece of cassette tape (see How Cassette Tapes Work for details). A magstripe reader can understand the information on the three-track stripe. If the ATM isn’t accepting your card, your problem is probably either: a dirty or scratched magstripe or an erased magstripe (The most common causes for erased magstripes are exposure to magnets, like the small ones used to hold notes and pictures on the refrigerator, and exposure to a store’s electronic article surveillance (EAS) tag demagnetizer.) There are three tracks on the magstripe. Each track is about one-tenth of an inch wide. The ISO/IEC standard 7811, which is used by banks, specifies; Track one is 210 bits per inch (bpi), and holds 79 6-bit plus parity bit read-only characters. Track two is 75 bpi, and holds 40 4-bit plus parity bit characters. Track three is 210 bpi, and holds 107 4-bit plus parity bit characters. Your credit card typically uses only tracks one and two. Track three is a read/write track (which includes an encrypted PIN, country code, currency units and amount authorized), but its usage is not standardized among banks. Smart Cards; these are yet another innovation; 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.
