Bank card, how does it work ?

Abusively called “Blue card“ in France (confusion with the card issuer name which has since disappeared), Bank Cards or CBs are small pieces of rectangular plastic containing at least :

  • A plastic support on which several information is printed
  • A magnetic strip containing this same informations and some others detailed below.
  • And in the best of cases, these cards contain a chip, minicomputer with its own microprocessor, its buffer memory and a protected memory containing secrets.

Smart card diagram

Nano computer

A few years ago, this mini-computer was only powered when the contacts “touched” those of a distributor (ATM / ATM / ATM) or a payment terminal (TPE), but since the advent contactless (NFC for Near Field Communication), it can be powered… without contact.

For the history, the contactless payment is strongly pushed by North America (USA + Canada) after a study showing that with the NFC, the customers consumed 15 to 20% more. It is understandable, because there, they do not use (or very little) the chip and a payment by CB remains long, because it is necessary to sign a bill.

Card issuers

There are 3 main ones :

Each has its own payment network, which means that, before the advent of internet payments, without an economic interest group (GIE CB chez nous), in some countries, merchants only accept VISA or Mastercard.

In France, CB network makes it possible to have an intermediary network simplifying compatibility, but this is going to change. In future payments, you may have to choose which network you want to pay through.

More details, read here

Bank card informations


– Chip

– Holder name

– Expiration date

– Famous card number or his real name : Primary Account Number/PAN

– Sometimes you also have a hologram that is supposed to prevent copying. In case of CCs12 card there are two holograms


– Magnetic strip

– PAN backside of legible print imprint

– Three-digit visual cryptogram, which has several names : Card Validation Code / CVC at Mastercard, Card Verification Value / CVV at Visa…

– A signature area to make life easier for American offenders who steal a card and have to sign a bill to confirm a purchase

– General conditions explaining to you that you are not the card owner !

Magnetic strip contents

The magnetic strip content is called “Track 2” and contains 37 numeric characters coded on 5 bits to manage the parity and therefore the error correction. Discretionary data is left to the discretion of the card issuer.

In VISA, in general, data contains : Expiration date, Service code which describes card use (withdrawal, only purchase, functional internationally …).

At Mastercard, there is more information : Expiration date, Service code, Discretionary data sometimes containing the CVV, a code, encrypted PIN…

Famous Bank card number
or Primary Account Number (PAN)

The PAN, along with the expiration date, is a bit like sesame because it allows you to make payments online, sometimes without requiring the cryptogram. It consists of two main parts :

– Bank code, older « Bank Identification Number / BIN » and now calles « Issuer identification number / IIN », composed of two parts : card issuer code (Visa, Mastercard, American Express, Discover …) and bank code.

–  Card number.

PAN has a size ranging from 13 to 19 digits, but in France, it generally has a size of 16 digits grouped 4 by 4.

Cut can thus be broken down as you can see in this picture.

All the possible values for a card number are not necessarily valid and for that, they must check Luhn’s formula, which consists in making the sum of each digit by multiplying by 2 those of the odd ranks (with the particularity that if the sum exceeds 9, sum the 2 digits, so 6×2-> 12 -> 1 + 2 -> 3). The result must be a multiple of 10.

4 9 7 8  8 7 3 8  6 3 6 9  8 0 0 7

8 9 5 8 7 7 6 8 3 3 3 9 7 0 0 7 (here we multiply the numbers in odd rows by 2)


PAN is valid !

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