According to the CB Observatory, nearly 73 million bank cards are in circulation in France. On each of them, a series of numbers, enigmatic at first sight. However, the 16 numbers on your credit card owe nothing to chance. Explanations.
No doubt you have already noticed them on your bank card: 16 digits, spars into 4 groups of 4 digits. But did you know that these numbers are not there? by accident? Their scheduling actually obeys specific rules.
In detail, these inscriptions follow a mathematical formula known asLuhn’s algorithm. A sophisticated encryption system, thanks to which it is possible to check the numbers of your CB via a control key.
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What do the 16 digits on your credit card mean?
The first digit identifies the industry your card is from: 1 and 2 for airlines, 3 for travel or leisure organisations, 4 and 5 for banking and financial establishments, 6 for merchandising, 7 for oil, 8 for telecommunications and 9 for national media.
The first 6 digits refer to the issuing institution from the menu. For example, a Visa card always starts with a 4, while a Mastercard always starts with 51 or 55. At American Express, this sequence of numbers starts with 34 or 37.
The 7th digit and the following (except the last) are used identify your card within the establishment with a single suite. This channel consists of 9 digits, or 1 billion combinations. If necessary, it can however be extended to 12 digits, thus generating 1000 billion additional possibilities.
Not enough to scare hackers though. According to a study by NordVPN, they can use the computing power modern computers to guess the digits of your bank card in the space of 6 seconds.
Finally, the last digit acts as an authentication key. It is used to check the validity of the card using Luhn’s algorithm.
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How to recover a fake credit card?
To check the validity of a bank card, take the 16 numbers written on the front. Then double every other digit starting with the penultimate digit. If you get a result greater than 9, add each unit (7 multiplied by 2 becomes for example 14, or 1+4 = 5).
To finish, add up obtained digits and remaining digits. If the result can be divide by 10, the card is valid. Otherwise, it is a fake credit card.
An example?
Let’s do a test with the following credit card number: 4417123456789113
Here, we start by removing the last digit (3).
Then we multiply a number by 2:
2×1 = 2 2×9 = 18 = 1+8 = 9 2×7 = 14 = 1+4 = 5 2×5 = 10 = 1+0 = 1 2×3 = 6 2×1 = 2 2×1 = 2 2×4 = 8
Finally, we add the results obtained to the other figures:
2+9+5+1+6+2+2+8+4+7+2+4+6+8+1+3 = 70
In this example, 70 is a multiple of 10. The card is therefore valid.
Why are these numbers printed on your card?
As we have seen, the figures on your bank card are not there by chance. They make it possible to identify the organization which issued the card, but also the bank to which it is attached and its holder (you). This information allows you to to make the connection between your bank card and your current account during a transaction.
However, these data are already contained in the chip and the magnetic stripe of your card. It is also on these media that an electronic payment terminal (TPE) will seek the information necessary to authorize the transaction when you checkout.
So why print these numbers on your card? Answer: if in France the vast majority of shops are today equipped with TPE capable ofinterrogate the chip of your card, this is not always the case abroad. During a trip, it happens that a trader is obliged to check and enter manually the digits of your card on his payment terminal.
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