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Tuesday, October 30, 2007

Interesting calculation with your Credit Card Number

Credit Crunch of America has shaken the world economy to some extent. It may take some more time for this shaking to settle down. Who knows what are to happen within this short time?
The Chairman of the International Monetary Fund says that Dollar Has more Room to Fall over the next several years. He says that Euro is "very near" its equilibrium value. A person, facing disturbance in his physical state, will manage to balance himself to retain his original conditions of stability. This is the time the world economy is trying similarly to balance and correct itself.

People who could not afford have purchased houses availing loans for thousands of dollars and ultimately become unable to repay… As a result, all these problems have developed.

Even in India, this credit disturbance (Loan offers) is increasing day by day. For all countries, this is a lesson to learn from America, to realize how risky it is going to be to avail loans beyond repayment capacity.

Okay, let it be there. Do you know that there is some interesting calculation in your Credit Card Number? You can identify whether your card is a VISA card or a MASTERCARD card from its number itself. In general, the numbers of MASTERCARD type cards will start with 51-55. The numbers of VISA cards will start with 4.

Assume that you are shopping online as usual. You can see e-commerce facility, that is, some provision for the customers to make payments online at many websites. Such websites just by glancing at your credit card will be able to say whether the card is valid or fake. Then only, they will start financial transactions. How is this possible? Check digit algorithm MOD 10, that is, a formula, known as LUHN, comes into the scene for helping in such a validation process. You too can easily identify if a credit card number is valid or fake by applying this method of calculation.

See, here is the formula.

Leaving the right most number, double the alternate digits starting from the right side.
Then add all numbers. That is all. If the last digit of the answer is zero, (as in 30, 40, 50, etc) then it is a valid credit card number.
For example, let us assume that my credit card number is 49927398716.

The following is the outcome of applying the method.
4 9x2 9 2x2 7 3x2 9 8x2 7 1x2 6

The numbers we got by doubling the alternate digits (leaving the extreme right digit 6) are:
18 4 6 16 2

When you add these numbers now, you must take the two digit number 18 as 1+8 and the two digit number 16 as 1+6.

Now add all numbers.
4 + (1+8) + 9 + (4) + 7 + (6) + 9 + (1+6) + 7 + (2) + 6

Answer is 70. Therefore, this is, no doubt, a valid credit card number.
See another example in the picture. It is a fake credit card number.

This formula on Excel
This formula on Java
This formula on C#

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