Credit cards

 

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.

 
 
 
 
 
 

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 iron-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.

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:

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.

The information on track one is contained in two formats: A, which is reserved for proprietary use of the card issuer, and B, which includes the following:

• Start sentinel - one character
• Format code="B" - one character (alpha only)
• Primary account number - up to 19 characters
• Separator - one character
• Country code - three characters
• Name - two to 26 characters
• Separator - one character
• Expiration date or separator - four characters or one character
• Discretionary data - enough characters to fill out maximum record length (79 characters total)
• End sentinel - one character
• Longitudinal redundancy check (LRC) - one character LRC is a form of computed check character.

 

The format for track two, developed by the banking industry, is as follows:

• Start sentinel - one character
• Primary account number - up to 19 characters
• Separator - one character
• Country code - three characters
• Expiration date or separator - four characters or one character
• Discretionary data - enough characters to fill out maximum record length (40 characters total)
• LRC - one character

 

There are three basic methods for determining whether your credit card will pay for what you're charging:

• Merchants with few transactions each month do voice authentication using a touch-tone phone.
• Electronic data capture (EDC) magstripe-card swipe terminals are becoming more common -- so is swiping your own card at the checkout.
• Virtual terminals on the Internet

 

This is how it works: After you or the cashier swipes your credit card through a reader, the EDC software at the point-of-sale (POS) terminal dials a stored telephone number (using a modem) to call an acquirer. An acquirer is an organization that collects credit-authentication requests from merchants and provides the merchants with a payment guarantee.

When the acquirer company gets the credit-card authentication request, it checks the transaction for validity and the record on the magstripe for:

• Merchant ID
• Valid card number
• Expiration date
• Credit-card limit
• Card usage

 

Single dial-up transactions are processed at 1,200 to 2,400 bits per second (bps), while direct Internet attachment uses much higher speeds via this protocol. In this system, the cardholder enters a personal identification number (PIN) using a keypad.

The PIN is not on the card -- it is encrypted (hidden in code) in a database. (For example, before you get cash from an ATM, the ATM encrypts the PIN and sends it to the database to see if there is a match.) The PIN can be either in the bank's computers in an encrypted form (as a cipher) or encrypted on the card itself. The transformation used in this type of cryptography is called one-way. This means that it's easy to compute a cipher given the bank's key and the customer's PIN, but not computationally feasible to obtain the plain-text PIN from the cipher, even if the key is known.

This feature was designed to protect the cardholder from being impersonated by someone who has access to the bank's computer files.

Likewise, the communications between the ATM and the bank's central computer are encrypted to prevent would-be thieves from tapping into the phone lines, recording the signals sent to the ATM to authorize the dispensing of cash and then feeding the same signals to the ATM to trick it into unauthorized dispensing of cash. 

"Smart" credit card

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. 
 
 
 
 

Interest charges 

Credit card issuers usually waive interest charges if the balance is paid in full each month, but typically will charge full interest on the entire outstanding balance from the date of each purchase if the total balance is not paid.

For example, if a user had a $1,000 transaction and repaid it in full within this grace period, there would be no interest charged. If, however, even $1.00 of the total amount remained unpaid, interest would be charged on the $1,000 from the date of purchase until the payment is received. The precise manner in which interest is charged is usually detailed in a cardholder agreement which may be summarized on the back of the monthly statement. The general calculation formula most financial institutions use to determine the amount of interest to be charged is APR/100 x ADB/365 x number of days revolved. Take the annual percentage rate (APR) and divide by 100 then multiply to the amount of the average daily balance (ADB) divided by 365 and then take this total and multiply by the total number of days the amount revolved before payment was made on the account. Financial institutions refer to interest charged back to the original time of the transaction and up to the time a payment was made, if not in full, as RRFC or residual retail finance charge. Thus after an amount has revolved and a payment has been made, the user of the card will still receive interest charges on their statement after paying the next statement in full (in fact the statement may only have a charge for interest that collected up until the date the full balance was paid, i.e. when the balance stopped revolving).

The credit card may simply serve as a form of revolving credit, or it may become a complicated financial instrument with multiple balance segments each at a different interest rate, possibly with a single umbrella credit limit, or with separate credit limits applicable to the various balance segments. Usually this compartmentalization is the result of special incentive offers from the issuing bank, to encourage balance transfers from cards of other issuers. In the event that several interest rates apply to various balance segments, payment allocation is generally at the discretion of the issuing bank, and payments will therefore usually be allocated towards the lowest rate balances until paid in full before any money is paid towards higher rate balances. Interest rates can vary considerably from card to card, and the interest rate on a particular card may jump dramatically if the card user is late with a payment on that card or any other credit instrument, or even if the issuing bank decides to raise its revenue. 
 

Benefits to customers 

The main benefit to each customer is convenience. Compared to debit cards and cheques, a credit card allows small short-term loans to be quickly made to a customer who need not calculate a balance remaining before every transaction, provided the total charges do not exceed the maximum credit line for the card. Credit cards also provide more fraud protection than debit cards. In the UK for example, the bank is jointly liable with the merchant for purchases of defective products over £100.

Many credit cards offer rewards and benefits packages, such as offering enhanced product warranties at no cost, free loss/damage coverage on new purchases, and points which may be redeemed for cash, products, or airline tickets. Additionally, carrying a credit card may be a convenience to some customers as it eliminates the need to carry any cash for most purposes. 

Detriments to customers 

High interest and bankruptcy

Low introductory credit card rates are limited to a fixed term, usually between 6 and 12 months, after which a higher rate is charged. As all credit cards charge fees and interest, some customers become so indebted to their credit card provider that they are driven to bankruptcy. Some credit cards often levy a rate of 20 to 30 percent after a payment is missed; in other cases a fixed charge is levied without change to the interest rate. In some cases universal default may apply: the high default rate is applied to a card in good standing by missing a payment on an unrelated account from the same provider. This can lead to a snowball effect in which the consumer is drowned by unexpectedly high interest rates. Further, most card holder agreements enable the issuer to arbitrarily raise the interest rate for any reason they see fit. As of December 2009, First Premier Bank is reportedly offering a credit card with a 79.9% interest rate.

Inflated pricing for all consumers

Merchants that accept credit cards must pay interchange fees and discount fees on all credit-card transactions. In some cases merchants are barred by their credit agreements from passing these fees directly to credit card customers, or from setting a minimum transaction amount (no longer prohibited in the United States). The result is that merchants may charge all customers (including those who do not use credit cards) higher prices to cover the fees on credit card transactions. In the United States in 2008 credit card companies collected a total of $48 billion in interchange fees, or an average of $427 per family, with an average fee rate of about 2% per transaction. 

Grace period

A credit card's grace period is the time the customer has to pay the balance before interest is assessed on the outstanding balance. Grace periods may vary, but usually range from 20 to 50 days depending on the type of credit card and the issuing bank. Some policies allow for reinstatement after certain conditions are met.

Usually, if a customer is late paying the balance, finance charges will be calculated and the grace period does not apply. Finance charges incurred depend on the grace period and balance; with most credit cards there is no grace period if there is any outstanding balance from the previous billing cycle or statement (i.e. interest is applied on both the previous balance and new transactions). However, there are some credit cards that will only apply finance charge on the previous or old balance, excluding new transactions.

Benefits to merchants

For merchants, a credit card transaction is often more secure than other forms of payment, such as cheques, because the issuing bank commits to pay the merchant the moment the transaction is authorized, regardless of whether the consumer defaults on the credit card payment (except for legitimate disputes, which are discussed below, and can result in charges back to the merchant). In most cases, cards are even more secure than cash, because they discourage theft by the merchant's employees and reduce the amount of cash on the premises.

Prior to credit cards, each merchant had to evaluate each customer's credit history before extending credit. That task is now performed by the banks which assume the credit risk. Credit cards can also aid in securing a sale, especially if the customer does not have enough cash on his or her person or checking account. Extra turnover is generated by the fact that the customer can purchase goods and/or services immediately and is less inhibited by the amount of cash in his or her pocket and the immediate state of his or her bank balance. Much of merchants' marketing is based on this immediacy.

For each purchase, the bank charges the merchant a commission (discount fee) for this service and there may be a certain delay before the agreed payment is received by the merchant. The commission is often a percentage of the transaction amount, plus a fixed fee (interchange rate). In addition, a merchant may be penalized or have their ability to receive payment using that credit card restricted if there are too many cancellations or reversals of charges as a result of disputes. Some small merchants require credit purchases to have a minimum amount to compensate for the transaction costs.

In some countries, for example the Nordic countries, banks guarantee payment on stolen cards only if an ID card is checked and the ID card number/civic registration number is written down on the receipt together with the signature. In these countries merchants therefore usually ask for ID. Non-Nordic citizens, who are unlikely to possess a Nordic ID card or driving license, will instead have to show their passport, and the passport number will be written down on the receipt, sometimes together with other information. Some shops use the card's PIN for identification, and in that case showing an ID card is not necessary. 

Costs to merchants

Merchants are charged several fees for the privilege of accepting credit cards. The merchant is usually charged a commission of around 1 to 3 per-cent of the value of each transaction paid for by credit card. The merchant may also pay a variable charge, called an interchange rate, for each transaction. In some instances of very low-value transactions, use of credit cards will significantly reduce the profit margin or cause the merchant to lose money on the transaction. Merchants must accept these transactions as part of their costs to retain the right to accept credit card transactions. Merchants with very low average transaction prices or very high average transaction prices are more averse to accepting credit cards. In some cases merchants may charge users a "credit card supplement", either a fixed amount or a percentage, for payment by credit card. This practice is prohibited by the credit card contracts in the United States, although the contracts allow the merchants to give discounts for cash payment. 
 
 
 
 
 
 
 

Parties involved 

• Cardholder: The holder of the card used to make a purchase; the consumer.
• Card-issuing bank: The financial institution or other organization that issued the credit card to the cardholder. This bank bills the consumer for repayment and bears the risk that the card is used fraudulently. American Express and Discover were previously the only card-issuing banks for their respective brands, but as of 2007, this is no longer the case. Cards issued by banks to cardholders in a different country are known as offshore credit cards.
• Merchant: The individual or business accepting credit card payments for products or services sold to the cardholder.
• Acquiring bank: The financial institution accepting payment for the products or services on behalf of the merchant.
• Independent sales organization: Resellers (to merchants) of the services of the acquiring bank.
• Merchant account: This could refer to the acquiring bank or the independent sales organization, but in general is the organization that the merchant deals with.
• Credit Card association: An association of card-issuing banks such as Visa, MasterCard, Discover, American Express, etc. that set transaction terms for merchants, card-issuing banks, and acquiring banks.
• Transaction network: The system that implements the mechanics of the electronic transactions. May be operated by an independent company, and one company may operate multiple networks.
• Affinity partner: Some institutions lend their names to an issuer to attract customers that have a strong relationship with that institution, and get paid a fee or a percentage of the balance for each card issued using their name. Examples of typical affinity partners are sports teams, universities, charities, professional organizations, and major retailers.

 
 
 
 
 

Transaction steps 

Authorization: The cardholder pays for the purchase and the merchant submits the transaction to the acquirer (acquiring bank). The acquirer verifies the credit card number, the transaction type and the amount with the issuer (Card-issuing bank) and reserves that amount of the cardholder's credit limit for the merchant. An authorization will generate an approval code, which the merchant stores with the transaction.